Pricing hacks of online retailers

1. Free stuff

When retailers offer products and services for "free" there's usually an ulterior motive. For online shops, "free" provides the initial incentive for buyers to use their web site, and may be effective in retaining customer loyalty. One of the most common uses of "free" is free delivery.

Example

UK-based The Book Depository is without doubt using the power of free. The title of their home page is "Free delivery worldwide on all books from The Book Depository". This title shows up in google when searching for "book depository", along with the site's description, which is "The Book Depository offers over 8 million books with free delivery worldwide". The site's byline is "The Book Depository. Free delivery worldwide on all our books". Also in a prominent position on the home page is: "Free worldwide delivery" which links to a page listing all of the countries where they offer free delivery.

2. Per customer limits and the perception of product scarcity

Per customer limits leads buyers to think that a product is scarce, and increases their incentive to buy now. It also entices people to buy more than they originally intended. The legitimate reason for doing this - to avoid products getting sold on the gray market - is hardly ever a real concern. Retailers will also impose a time limit during which the product is available, along with a ceiling on the number of products that can be sold, after which the deal will end.

Example

Living Social Deal - Laser Nail Therapy Clinic - 70% Off Laser Nail Fungus Removal for Feet ($450)
This group buying deal shows a "Limit 4 per customer" in the fine print. Most group buying sites have per customer limits for all their deals. In additon to the per customer limit, there is an absolute limit on how many deals can be sold, as well as the deal only being available for a limited amount of time, in this case, 7 days.

3. The 9 factor - prices ending in 9, 99 or 95

Using prices that end in 9, 99, or 95 is called 'Charm Pricing' or 'Psychological Pricing'. We've been culturally conditioned to associate these prices with discounts. And because we read numbers from left to right, we mentally encode a price like $7.99 as $7, especially when we quickly glance at the price. That's called the "left-digit effect" - it's encoded in our minds before we have finished reading all of the digits.

Example

Pricing of the Amazon Kindle family of products - $499, $199, $119.
As opposed to $500, $200, $120.

4. Easy math

Most sites, when putting a product on sale, will show you what price it was marked down from. It might be "was $20, now $15". You will rarely see something like, "was $20, now $14.22." The reason is that if the difference is easy to calculate, we tend to think it's a better deal. It's called "computation fluency". Another method employed by many sites is to display the amount of the total saving along with the percentage saved.

Example

The Body Shop USA - 50% off Sitewide - After Christmas Sale. Everything is 50% off, making the amount you are saving obvious; you don't need to check any prices or fineprint. Anything you buy on their site will include a significant saving.

5. Sale price font size and color

A common practice in online sales is to display the sale price in a different font size and/or color to the original list price. Typically, the original list price will be shown in strike-though.

Example

Amazon uses red text to denote a sale price, shown below the original list price, which is struck out and shown in light gray. However, products which are not on sale and are being sold at the original list price continue to use this red (sale price) font. One theory says that customers will become accustomed to seeing red text as a saving, and will be more inclined to buy, even when the product is actually not on sale.

6. Dynamic Pricing (also known as Time-Based Pricing)

The airline industry is often cited as a dynamic pricing success story. It employs the technique so well that most of the passengers on any given airplane have paid different ticket prices for the same flight. By responding to market fluctuations or large amounts of data gathered from customers - ranging from where they live to what they buy to how much they have spent on past purchases - dynamic pricing allows companies to adjust the prices of identical goods to correspond to a customer’s willingness to pay.

Example 1

During Thanksgiving week, The New York Times tracked the price of Dance Central 3, a popular Xbox game, as it dropped on Amazon from $49.96 to $24.99 to $15.

Example 2

Coca-Cola tested dynamic pricing in automated vending machines where prices would fluctuate based on the surrounding temperature. Their theory was a soft drink would be worth more when it is hotter outside, and correspondingly, demand for soft drinks would decrease if it were cold outside. It was an unpopular idea and luckily, Coca-Cola abandoned it.

Sidenote

Oren Etzioni, a computer science professor at the University of Washington, became incensed when he found out that the traveller sitting next to him on a flight got a much better price for his ticket than he did. Etzioni started collecting online price data from all US airlines, then he created his own formula that could predict when the airlines would raise or lower their prices. His company was bought by Microsoft. And today, when you search for flights on Microsoft's Bing Travel site, you'll see colour coded arrows (called the "price predictor") letting you know you if the price of that ticket is likely to head up or down.

7. Pay what you want

Pay what you want is a pricing system where buyers pay any desired amount for a given product or service, sometimes including paying nothing (i.e. free). Sometimes a minimum (floor) price may be set, or a suggested price may be indicated to the buyer. The buyer can also pay an amount higher than the standard price.

It has the benefit of reducing buyer's remorse, which is what happens when you decide afterwards that you've paid too much for a product. It also can result in a viral increase in popularity or visibility for a product when used in highly competitive markets.

It is often used for products which use digital delivery, such as software and music. There is usually no additional cost per download to the seller anyway, since the site's bandwidth would usually be paid for on a capped, monthly basis.

Example 1

Freeware software is often distributed under this model. For example, on the home page of Paint.net is the message "Show your appreciation for Paint.NET and support future development by donating!". Typically, a PayPal donate button is used.

Example 2

In October 2007, Radiohead released their seventh album, In Rainbows, through the band's website as a digital download and requested fans just pay whatever amount they thought it was worth.

Example 3

Introduced during May 2010, the Humble Bundle was a set of six downloadable indie games which were distributed using a pay what you want system (with inclusion of a buyer-controllable charitable contribution).

8. Freemium

Freemium is a business model that works by offering a base product or service free of charge (typically digital offerings such as software, games or online software - software as a service). A premium is then charged for advanced features, functionality, or for related products and services.

Example 1

LinkedIn - Basic features of the social network are available for free. For the ability to see the profile of members outside your network, and to access advanced features, you'll need to pay.

Example 2

The New York Times paywall. A limited number of news articles can be read for free per month. To get full access to the site, you'll need to pay.

Example 3

Zynga publishes games for Facebook and the major smartphone/tablet app stores. Typically there are in-game actions (e.g. farming) which result in being rewarded with an in-game currency (e.g. loot/coins/points). The in-game currency can then be used to buy additional game features, or to progress further in the game. The in-game currency can be topped up, via a payment to Zynga in real dollars via an in-app-purchase.

9. No dollar signs

A 2009 Cornell University study found that diners in upscale restaurants spent significantly less when menus contained the word "dollars" or the symbol "$". Restaurants use the technique of omitting dollar signs to get you to focus on the product being sold (the food) rather than the price. They may also mention or profile the chef who is cooking the food. Apart from the websites of restaurants, its difficult to see this being used much in general online retailing.

Example

Gramercy Tavern, New York City
According to Urbanspoon this is the most popular fine dining restaurant in New York City.There's no dollar signs at all on their website, and their a la carte lunch menu (pdf) doesn't feature any dollar signs either, only numbers.

10. "X for $X"

Buyers will often buy more of a product than they originally intended, if it means they will secure a bargain.

Example

Bath and Body Works - 5 for $5 sale
In this case you need to buy 5 products to realise a saving of 33% off the original list price.

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Defensive copy and paste coding

I've got into the habit of doing this check at the end of any development which has involved some copy & pasting of existing code. It's been useful for me in picking up issues before build/test/commit.

It just involves getting a reference count of all occurrences the new variable (or function) compared with the old variable (or function)...

• Select the newly added variable (or function) name
• Right-click to bring up the context menu
• Select the "Find all references" option

The screenshot shown is from Visual Studio, but this feature is also available in other IDEs and editors, such as Eclipse (via the "References" context menu). Alternatively, if you're not using an IDE, a simple text search across all files in your project will be just as useful, assuming that the search string is unique within your project.

Often, you'd expect the reference count should match with the one you've copy & pasted from (as shown above). If it doesn't match, then by looking at the references which are different, you should be able to easily reason about why, and whether its expected or not. If its unexpected, that could mean there's an error in your code.

So who admits to copy & paste coding - isn't it a sign of bad programming? ... if you can copy & paste big blocks of code, followed by only a few small changes then that's a code smell - you should probably extract the common code into a new function and call it twice. Agreed on that, but there is still many cases where you do have a valid reason to copy existing code. One example is to make fine grained changes to some logic, when it might not be worth the additional complexity of creating a generic function to handle both cases. Or in the case shown above, when I'm copying the declaration of a collection member.

This is a pretty simple and obvious technique, and it might be well known to many already, but I thought I'd mention it anyway. It can also be used outside of the copy & paste case - just mentioning it here because that's the case I've used it more often.

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The slow decline of PCs and the fast rise of Smartphones/Tablets was predicted in 1993

I've just read some predictions for the future of the PC, written in 1993, by Nathan P. Myhrvold, the former Chief Technology Officer at Microsoft.

His memo is amazingly accurate. Note that his term "IHC" (Information Highway Computer) could be roughly equated with today's smartphone or tablet device, connecting to the Internet via WiFi or a cellular network. In his second last paragraph, Myhrvold predicts the winners will be those who "own the software standards on IHCs" which could be roughly equated with today's app stores, such as those on iOS (Apple), Android (Google, Amazon) and Windows 8 (Microsoft).

The only thing you could say he possibly didn't foresee would be the importance of hardware design in the new smartphone and tablet industry. I'd suggest that Apple achieved such a head start on their competition through a combination of both cutting edge hardware design along with their curated app store model for distributing software. Interestingly, Microsoft has only last month entered the hardware game with their new Surface brand tablets for Windows 8 and Windows RT, and also announced a shift to focus on becoming a "Devices and Services" company.

Note: the term "Cairo" used below is the code name for a Microsoft Research project which lasted from 1991 to 1996. It resulted in some features that were eventually rolled into Windows 95, IIS and SQL Server.


The below is an extract from a memo written by Nathan P. Myhrvold, titled "Road Kill on the Information Highway". September 8, 1993. Full Source. 

Personal Computers
I've saved the best for last.  Our own industry is also doomed, and will be one of the more significant carcasses by the side of the information highway.  The basic tasks that PCs are used for today will continue for a long as it makes sense to predict, so it isn't a question of the category disappearing.  The question is one of who will continue to satisfy these needs and how? 

As a case in point, consider that the fundamental category needs for mainframes and minicomputers also still exists and will continue to do so for a very long time.  Despite this, the companies involved are dying and the entire genre is likely to disappear.  The reason is that a new breed of machine - the PC - came along which out flanked them.  In the early years PCs were not particularly good at what minis and mainframes did, but they were terrific at a whole new set of problems that the traditional computing infrastructure had basically ignored.  

Personal productivity applications drove PCs onto millions of desks and created a very vital industry which grew faster - both in business terms and price/performance - than the mainframe and minicomputer markets.   The power conferred by this growth made PCs the tail which wagged the dog; free to ignore the standards which existed for mainframes and minis and move off on their own.   Over time the exponential growth in computing has finally (after 17 years) given the PC industry the technical ability to beat minis and mainframes in their own domain.   Although the early software platforms for PCs had to be extended to fully realize this potential (DOS to Windows to NT to Cairo), it turned out to be far easier to do this than to make mainframe or minicomputer systems address the new needs and applications.   Even within the heart of minicomputer and mainframe's domain - giant transaction processing applications etc., the old standards will not be used.  

I believe that the same thing will happen again with PCs playing the role of mainframes and minis, and the computing platforms of the information highway taking over the role of the challenger.   

The technical needs of computers on the information highway, or IHCs are quite different than for PCs.  The killer applications for IHCs in the early years will include video on demand, games, video telephony and other distributed computing tasks on the highway.  It is hard to classify this as either higher tech or lower tech than the software for PCs, because the two are quite different.   Most IHCs will certainly need to be cheaper than PCs by an order of magnitude and this will inevitably cause them to be less capable in many ways, but some of their requirements are far more advanced. 

Another way to say this is that the rich environment of software for PCs is largely irrelevant for IHCs.   Windows, NT, System 7 and Cairo do not solve the really important technical problems required for IHC applications, and it is equally likely that the early generations of IHC software won't be great platforms for PC style apps.  This isn't surprising because they are driven by an orthogonal set of requirements. 

The IHC world will almost certainly grow faster than PCs, both in business terms and in price/performance.   The PC industry is already reaching saturation from a business perspective.  Technically speaking, the industry is mired in hardware standards (Intel and Motorola CISC processors)  with growth rates that are flattening out relative to the state of the art - just as the 360/3090 and VAX architectures did.   The Macintosh and Windows computing environments may be able to survive the painful transition to new RISC architectures, but they will lose time and momentum in doing so.    

PCs will remain paramount within their domain for many years (we'll still have a computer on every desk) but IHCs will start to penetrate a larger and larger customer base on the strength of its new and unique applications.   The power of having the worlds information - and people - on line at any time is too compelling to resist.   For a long time people will still have a traditional PC to handle traditional PC tasks - in precisely the same way that they have kept their mainframes and minis for the last 17 years.   One day however people will realize that their little IHCs are more powerful and cheaper than PCs - just as we have finally done with mainframes.   There will be a challenge for the IHC software folks to write the new systems and applications software necessary to obviate PCs, just as we had to work pretty hard to come up with NT, but this battle will clearly go to the companies who own the software standards on IHCs.  The PC world won't have any more say about how this is done than the companies who created MVS or VMS did about our world.  Of course, some of the VMS people were involved, but as discussed above it is very hard for organizations to make the transition. 

This may sound like a rather dire prediction, but I think that for the most part it is inevitable.  The challenge for Microsoft is to be sufficiently involved with the software for the IHC world that we can be a strong player in that market.  If we do this then we will be able to exploit a certain degree of synergy between IHCs and PCs - there are some natural areas where there is benefit in having the two in sync.  The point made above is that those benefits are not sufficiently strong that they alone will give us a position in the new world.   We'll live or die on the strength of the technology and role that we carve out for ourselves in the brave new world of the information highway. 

Many thanks to Reddit user erpettie who originally submitted a link to this memo on /r/technology,which is how I came across it.

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Q&A With Nine Great Programmers

This Q&A article is originally from 2006, published on the blog of Polish developer Jaroslaw "sztywny" Rzeszótko (AKA "Stiff").  That original blog post is no longer online. Gratefully republished with his permission.

On a hot, boring afternoon I got an idea. With the help of publicly accessible e-mail addresses, I asked 10 questions to a bunch of programmers that I consider very interesting people and I respect them for various things they created. Coming out with the questions was a 5 minute job for me - these are things I would ask about if I could speak with them personally for, let’s say, 10 minutes, and I didn’t have time for thinking too much. The last two question don’t have anything to do with programming, this is simply something I like to know about everyone I talk to, lets say that’s my hobby. Not everyone wanted to answer them, and that’s fine. It was the first "interview" I ever made, so I also made some mistakes, which went out as people started answering. But despite this, I learnt a lot of interesting stuff, so it was definitely a valuable experience.

Not everyone responded to my e-mail, not everyone agreed to answer the questions, maybe I will also get some answers after I published this, I didn’t have the patience to wait longer, so new things may appear here over time (Update: Bjarne Stroustrup was added on 03.08.2006).
-- Jaroslaw

Starring

Linus Torvalds - The Linux kernel author.

Dave Thomas - Author of the "Pragmatic Programmer", "Programming Ruby" and other great books about programming. One can read his mainly programming-related thoughts here.

David Heinemeier Hansson - Author of the Rails Framework - the new hot web development framework. He has a blog here.

Steve Yegge - Probably one of the least known guys here, but he also sent most interesting answers. He has a popular blog about programming. He is also the author of a game called "Wyvern".

Peter Norvig - Research Director at Google, a well known Lisper, author of famous (in some circles at least) books about AI. See his homepage here.

Guido Van Rossum - The Python language creator.

Bjarne Stroustrup - C++ language creator, has a homepage here.

James Gosling - The Java language creator.

Tim Bray - One of the XML and Atom specifications author and a blogger too.


Q 1: How did you learn programming? Were any schools of any use? Or maybe you didn’t even bother with ending any schools :) ?

Steve Yegge
I taught myself to program on an HP calculator using their RPN stack language when I was 17 years old. I’d tried to learn programming a few times before that but never really "got" it. The HP 28c and 48g scientific calculators were pretty powerful and had great docs. I wrote a 3D wireframe viewer for the 48g — I got a book on 3D graphics and painstakingly translated an example program in Pascal into the RPN stack language. It was pretty sweet when I got it running. After that I bought a PC and Turbo Pascal, and started studying programming in earnest. I was a decently good programmer by the time I went into the CS program in college.

I went to the University of Washington and got an undergrad degree in CS. It was definitely worthwhile, and I recommend that all programmers should try to get a CS degree if possible.

Linus Torvalds
I didn’t learn programming in school, but mostly on my own reading books and just doing it (initially on a Commodore VIC-20, later on a Sinclair QL).

That said, I think especially University was very useful. Rather than go to an engineering school, I went to Helsinki University, which is pretty theoretical, so there the teaching concentrated not so much on programming (which was just a small part, and which I ended up doing more of "on the side" anyway), but most of the courses tended to be on fundamental concepts and things like complexity analysis. Which can seem boring and even a waste of effort at times, but I think it was useful, and I mostly enjoyed it. And I think I’m probably a better programmer for it.

David Heinemeier Hansson
I learned programming by starting to put together my first web page in HTML. Then I wanted to make some dynamic pieces and picked up first ASP then PHP. After I already knew how to program, I then started on a joint computer science and business administration degree.

Peter Norvig
I took courses in high school and college, but always felt I learned more on my own.

Dave Thomas
During my secondary schooling I took a class in a local technical college on computers. It got me totally hooked: I fell in love with programming, and looked around for colleges offering courses in software. Eventually I went to Imperial College, part of London University. It was only the second year they’d offered a course in software, and it was absolutely marvelous: the staff and students worked together to make the materials better, and everyone learned a lot. The undergraduate course there gave me an incredibly strong background in software development. I stayed on to start a PhD, but got lured away by a startup.

But the overall question is "how did you learn programming?" The real answer to that is "I’m still learning programming." I think any good developer continues to learn throughout their careers. It isn’t just a question of picking up new languages and libraries: good developers also refine their techniques and practices over the years.

Guido Van Rossum
I went to university where they had a big mainframe and there were various computer courses. This was very important for me.

James Gosling
Initially, I was self-taught. I got my first programming job before I went to college. But I’m glad I did. I had a lot of fun. I kept going until I had a PhD.

Bjarne Stroustrup
In university (Aarhus and later Cambridge). The universities taught me much that was useful, incl. most of the bases for my future work. In addition, I learned a fair bit from programming for money - where understanding of real-world problems, correctness, maintainability, on-time delivery, etc. were more pressing than in an educational setting.

Tim Bray
I thought I was going to be a math teacher. The math program at University required a few computer science courses.


Q 2: What do you think is the most important skill every programmer should posses?

Steve Yegge
Written and verbal communication skills. You’ll never make it very far as a programmer in any field unless you can get your ideas across to people effectively. Programmers should read voraciously, practice writing, take writing courses, and even practice at public speaking.

Linus Torvalds
It’s a thing I call "taste".

I tend to judge the people I work with not by how proficient they are: some people can churn out a lot of code, but more by how they react to other peoples code, and then obviously by what their own code looks like, and what approaches they chose. That tells me whether they have "good taste" or not, and the thing is, a person without "good taste" often is not very good at judging other peoples code, but his own code often ends up not being wonderfully good.

But hey, it’s not the only thing. One thing that is very useful, especially in an open source project, is simply the ability to communicate well what you want to do, and how you are going to do it. The ability to explain to others why you do something a certain way is very important, and not everybody has that ability.

That said, in the end there are also the people who just churn out good code. They may not be good at explaining it, and they may not even have great taste, but the code works well. Sometimes you need another person (one that does have that hard-to-define "taste") to maybe massage the code into a form where it’s useful in the bigger picture, but just the ability to write clear code for difficult problems is obviously a fairly fundamental part of any programmer.

David Heinemeier Hansson
A strong sense of value. The ability to ask yourself the question: Is it worth doing what I’m doing right now? So many programmers seem to waste oceans of time on stuff that just doesn’t matter. And not enough on the stuff that does.

Peter Norvig
I don’t think there’s one, but let’s say concentration.

Dave Thomas
Passion.

Guido Van Rossum
Your questions are rather general and hard to answer. :-) I guess being able to cook an egg for breakfast is invaluable.

James Gosling
To be self motivated. To be really good, you have to be in love with what you do.

Bjarne Stroustrup
The ability to think clearly: A programmer has to understand problems and express solutions.

Tim Bray
Ability to prefer evidence to intuition.


Q 3: Do you think mathematics and/or physics are an important skill for a programmer? Why?

Steve Yegge
There is a large branch of mathematics that’s very important for programmers called "discrete math" or "concrete math". It includes disciplines such as probability, combinatorics, graph theory, induction proofs, and other useful tools. I would encourage all programmers to study discrete mathematics to whatever extent they can. Even a little is better than none at all.

As for more traditional math, well, I don’t use it as often, but it comes in very handy when I need it. For instance, I’ve only used calculus once in the past year as part of my job. I had to estimate loads for the peak traffic hour of the day for a service whose load "follows the sun" in an approximate sine curve. The simplest way to make the estimate was to integrate over 1/24th of the curve at a specific time. If I hadn’t known calculus, I would not have known how to make a reasonably accurate estimate.

When I was writing my game, Wyvern, having a solid working knowledge of basic planar geometry was incredibly helpful. And it’s quite common to use algebra and linear algebra on a regular basis. But I rarely use trigonometry or differential equations on the job, and not much calculus either.

I’d say my basic math foundation has made me maybe 5% to 10% better as a programmer. If I knew a lot more math, I’d undoubtedly be a much better programmer than I am today, so I study and practice math several hours a week.

I love physics and I have an ongoing, lifelong quest to try to understand the underpinnings of quantum mechanics. But I’ve never personally found any physics very useful towards my job as a programmer. That would, of course, be diffferent if I were doing something in a physics domain, such as 3D game programming, or certain types of simulation.

Linus Torvalds
I personally think a fairly strong math background is a good thing. I’m not as sure about the physics side, but I’m convinced that understanding math and having a good background in it helps you to be a better programmer. If only because the mental models are similar - you can build up any kind of set of rules you want, but it should be self-consistent.

David Heinemeier Hansson
Not at all. At least not for the kind of business programming needed for web applications. I consider it much more important that someone is a good writer.

Peter Norvig
Yes. Many ideas are inherently mathematical: induction, recursion, logic, etc.

Dave Thomas
Maybe. But, to be honest, I haven’t seen much of a correlation either way between these types of discipline and good software developers.

However, I have seen a strong correlation between people who have some music in their background and programming skills. I have no idea why, but I suspect that some of the areas of the brain that make someone musical also make them good at software development.

Guido Van Rossum
Math, yes (for some parts; I don’t care for differential equations, but algebra and logic are important). Physics, I don’t think so except it’s always useful to be interested in many different things.

James Gosling
Yes! They teach you logic & deduction... To have an analytical eye. And there’s no replacement for mathematics when it comes to analyzing algorithms.

Bjarne Stroustrup
Depends on the programmer and the programming tasks. Some forms of math are frequently useful; physics less often so, but then learning physics is one of the best ways of learning practical math.

Tim Bray
In my case, I’ve almost never used my university-level math to support my programming.


Q 4: What do you think will be the next big thing in computer programming? X-oriented programming, y language, quantum computers, what?

Steve Yegge
I think web application programming is gradually going to become the most important client-side programming out there. I think it will mostly obsolete all other client-side toolkits: GTK, Java Swing/SWT, Qt, and of course all the platform-specific ones like Cocoa and Win32/MFC/etc.

It’s not going to happen overnight. It’s very slowly been going that direction for ten years, and it could well be another ten years before web apps "win". The tools, languages, APIs, protocols, and browser technology will all have to improve far beyond what you can accomplish with them today. But each year they get a little closer, and I’ve finally decided to switch all my own app development over to browser-based programming from now on.

Microsoft and Apple definitely don’t want this to happen, so a necessary first step will be for an open-source browser such as Firefox to achieve a dominant market position, which will in turn require some sort of Firefox-only killer app. (A killer app would be something like iTunes, something that everyone in the world wants to use, badly enough to download Firefox for it.)

Linus Torvalds
I don’t think we’ll see a "big jump". We’ve seen a lot of tools to help make all the everyday drudgery easier - with high-level languages and perhaps the integration of simple databases into the language being the main ones. But most of the buzz-words have been of pretty limited use.

For example, I personally believe that "Visual Basic" did more for programming than "Object-Oriented Languages" did. Yet people laugh at VB and say it’s a bad language, and they’ve been talking about OO languages for decades.

And no, Visual Basic wasn’t a great language, but I think the easy DB interfaces in VB were fundmantally more important than object orientation is, for example.

So I think there will be a lot of incremental improvements, and the hardware improvements will make programming easier, but I don’t expect any huge productivity help or revolutions in how people do things.

At least not until you start approaching real AI, and I don’t think real AI is going to be anything you will ever "program".

David Heinemeier Hansson
I try not to predict the future. I’m not a big believer in fortune telling. The best way to predict the future is to implement it.

Peter Norvig
Large-scale distributed processing.

Dave Thomas
The next big thing in computer programming will be eclipsed by the next–next big thing in programming, and so on, and so on. I’m kinda tired of the endless search for the big things, because while doing it people tend to forget about the real issues: getting the fundamentals right. We need to get a whole lot better at talking with our customers, focussing on delivering value, and taking pride in what we do. A developer who can do these things can deliver great software with any tool set, and won’t need to worry about tracking the fads and fashions.

Guido Van Rossum
Sorry, I’m not much of a crystal ball person. I predicted CGI about 5 years after it had been invented. :-)

James Gosling
The two issues I’m most concerned about now are coping with parallelism and complexity.

Bjarne Stroustrup
I don’t know, and I don’t like to guess.

Tim Bray
No idea.


Q 5: If you had three months to learn one relatively new technology, which one would you choose?

Steve Yegge
I do happen to have 3 months (part-time), and I’m spending it learning Dojo (http://dojotoolkit.org) and advanced AJAX and DHTML. I’m learning it by writing a fairly ambitious web application. Dojo’s really cool, and I’m sure it will only improve with time.

Linus Torvalds
Hmm. I’d really love to do FPGA’s, but I’ve always been too busy to really sit down and start learning. I love the notion of playing with hardware: it’s obviously one of the reasons I ended up doing operating systems, since that (along with compilers) is about as close as you can get to playing with the hardware, without actually designing or building it yourself.

David Heinemeier Hansson
Cocoa programming for the Mac.

Peter Norvig
I’d like to know Javascript better. Also flash.

Dave Thomas
If "new" means "new to Dave Thomas" then I think I’d take intensive piano lessons.

If "new" means technology stuff, then I guess I’d choose technologies related to accessibility for people with disabilities.

Guido Van Rossum
Snowboarding.

James Gosling
For fun, I’d catch up on the latest in 3D rendering. I’d probably write a photon-map renderer.

Bjarne Stroustrup
There are very few things of any importance that you can learn in three month. I think you must be thinking of training in a well established field.

Tim Bray
Security, encryption, digital signatures, identity, etc. It’s a big problem for me that I’ve never learned this stuff.


Q 6: What do you think makes some programmers 10 or 100 times more productive than others?

Steve Yegge
I think if you pause to consider why not all atheletes are equally good, you’ll have your answer(s). Thomas Edison has a relevant quote about genius that might also provide you some clues.

Linus Torvalds
I really have no idea. I think some people are just better able to concentrate on the things that matter, and I think a lot of it is just doing it. Most of the really good programmers I know started doing it fairly young.

David Heinemeier Hansson
The ability to restate hard problems as easy ones.

Peter Norvig
The ability to fit the whole problem into their heads at one time.

Dave Thomas
They care about what they do.

Guido Van Rossum
Genetically different brain structure.

James Gosling
They think about what they do. They don’t rush in and slap things together. They have a holistic picture of what is to be built.

Bjarne Stroustrup
First a general lack of professionalism and adequate training. that sets the base level too low. Secondly, some people have a combination of "smarts" (ability to think clearly and get to the heart of things), experience, and knowledge of tools. Programming leaves more scope for that because it is a combination of theory and practice - neither of which is much use without domain knowledge.

Tim Bray
The surprising variability of the human mind.


Q 7: What are your favourite tools (operating system, programming/scripting language, text editor, version control system, shell, database engine, other tools you can’t live without) and why do you like them more than others?

Steve Yegge
OS: Unix! I use linux, cygwin, and darwin all about equally often now. You just can’t beat it for productivity tools. Every programmer should learn how to use every tool in /bin and /usr/bin.

Scripting language: Ruby. I’m proficient with just about every major scripting language out there: Perl, Python, Tcl, Lua, Awk, Bash, and others I’m forgetting. But I’m really lazy, and Ruby’s by far the easiest, so it’s a match made in heaven.

Programming language: I don’t have a favorite; I think they all suck. I tend to prefer Java because it’s a strong, portable platform with good tools and good libraries. But the Java language will evolve or die; it’s not good enough as-is to hold the lead indefinitely.

Text editor: Emacs, because it’s the best thing out there today.

Version control: SVN. Perforce is better, but it’s very expensive.

Shell: Bash, because I’m too lazy to learn a better one.

Database engine: MySQL, of course. Nothing else comes close.

Others: I find the GIMP invaluable, and also maddeningly unintuitive. I’ve been using it for years and can still barely do anything with it. But I couldn’t live without it, ironically enough.

Firefox is becoming an increasingly critical part of my tools lineup. I feel suffocated when I’m forced to use IE or Safari.

Note that all these tools (Unix, Emacs, Firefox, GIMP, MySQL, Bash, SVN, Perforce) have something in common: they’re extensible; i.e., they all have programming APIs. Great programmers learn how to program their tools, not just use them.

Linus Torvalds
I actually don’t end up having that many tools I work with, and for the many of them I have spent some time of my own to just make them work for me. The OS part is clearly the biggest one, but I’ve obviously also written my own version control system (git), and the text editor I use (micro-emacs) I’ve ended up customizing and extending upon too.

Other than those three parts, the only thing I care deeply about is my email reader. I use "pine" - not because it’s necessarily the greatest email reader ever, but because I’m used to it, and it does what I need it to do with a minimum of fuss.

David Heinemeier Hansson
OS X, TextMate, Ruby, Subversion, MySQL. That’s the combo currently keeping me happy. I like tools that exhibit good taste and a focus on the stuff that matters.

Peter Norvig
I dislike all three major OS - Windows, Mac, Linux. I like Python and Lisp. Emacs.

Dave Thomas
I switched to Macs a couple of years ago after being a Linux person for more than 10 years. The tools are not necessarily better, but they don’t have to be sharpened or maintained as often, which lets be concentrate on just using them.

I'm not a great believer in single tools: I tend to switch around quite frequently just so I can get experience with as many tools as possible. Right now I’m using OSX, Emacs, TextMate, Rails, Ruby, SVN, CVS, Rake, make, xsltproc, TeX, MySQL, Postgres, and a whole lot of small productivity aids. Who knows what I’ll be using next year.

Guido Van Rossum
Unix/Linux, Python, vi+emacs, Firefox.

James Gosling
These days I live in NetBeans. It does everything I want, very cleanly simply and efficiently. It’s the nicest environment I’ve ever lived in.

Bjarne Stroustrup
Unix, sam (a very simple text editor), and a good C++ compiler, of course.

Tim Bray
I like Unix-like operating systems, dynamic languages like Python and Ruby and statically-typed languages like Java (in particular the Java APIs), Emacs, whatever, bash, whatever, NetBeans.


Q 8: What is your favourite book related to computer programming?

Steve Yegge
Man, that’s a tough one. Maybe "Gödel, Escher, Bach: an Eternal Golden Braid" (Hofstadter)? Although it’s not strictly about programming. If you specifically mean "favorite book about programming", then maybe SICP (mitpress.mit.edu).

Linus Torvalds
Heh. When I read these days, I tend to either read fiction, or non-computer-related stuff (oldie but goodie: "The Selfish Gene" by Richard Dawkins).

When it comes to programming, the only real programming book that comes to mind is actually the classic Kernighan & Ritchie "The C Programming Language" book, because it’s such an incredibly useful book while being so very readable and short. Considering that you can basically learn one of the most important programming languages of our times from it, the fact that it’s thin and readable is just a wonder.

That said, many other books I enjoyed a lot were not about programming per se, but about computer architecture and hardware. There’s obviously Patterson & Hennessy’s computer architecture book, but for me personally perhaps even more Crawford & Gelsinger’s "Programming the 80386?, which was what I used when I started with Linux.

For similar reasons, I have a soft spot for Andrew Tanenbaum’s "Operating Systems: Design and Implementation".

David Heinemeier Hansson
I like Extreme Programming Explained for its rejection of common thinking about programming practices and Patterns of Enterprise Application Architecture for striking the right balance of abstract and concrete.

Peter Norvig
Structure and Interpretation of Computer Programs

Dave Thomas
It depends on what you mean by "favorite." Probably the best written book I’ve read in the area is IBM’s "IBM/360 Principles of Operation."

Guido Van Rossum
Neil Stephenson’s Quicksilver.

James Gosling
Programming Pearls by Jon Bentley.

Bjarne Stroustrup
K&R.

Tim Bray
Bentley’s Programming Pearls


Q 9: What is Your favourite book NOT related to computer programming?

Steve Yegge
Just one book? You’re asking for the impossible. There are too many great books out there to choose just one.

My favorite books that I’ve read this month are "Stardust" (Neil Gaiman) and "The Mind’s I" (Hofstadter/Dennet).

My favorite writers are Kurt Vonnegut, Jr. and Jack Vance.

Linus Torvalds
Well, I already mentioned the Selfish Gene by Dawkins. On the fictional side, there’s just a lot of books I’ve read and enjoyed, but few I’d say were my "favourite" one. I tend to not often re-read the books, and the selection would change over time. It’s mostly science fiction and fantasy, eg "Stranger in a Strange Land" by Heinlein was my favourite one as a teenager, but it’s a bit less clear-cut for me these days..

David Heinemeier Hansson
1984, George Orwell.

Guido Van Rossum
Neil Stephenson’s Quicksilver.

James Gosling
Guns, Germs & Steel by Jared Diamond

Bjarne Stroustrup
It changes over time. Currently O’Brian’s Aubrey/Maturin series.

Tim Bray
One Day in the Life of Ivan Denisovich


Q 10: What are your favourite music bands/performers/composers?

Steve Yegge
Favourite genres: classical, anime soundtracks, video-game music
Favourite composers: Rachmaninoff, Chopin, Bach
Favourite performers: David Russell (classical guitar), Sviatoslav Richter (piano)
Favourite anime OSTs: Last Exile, Haibane Renmei

Linus Torvalds
I'm actually not very much into music, but when I listen to it, I tend to listen to various classic-rockish things, ranging from Pink Floyd to the Beatles to Queen and The Who.

David Heinemeier Hansson
I like a lot of genres. Beth Orton, Aimee Mann, Jewel, Lauryn Hill. Actually, all those examples would fit under Girls with Guitars ;).

Guido Van Rossum
Philip Glass.

James Gosling
I tend to like folk musicians: Christine Lavin, Woody Guthrie, Pete Seeger...

Bjarne Stroustrup
Band: The Dixie Chicks. Composer: Beethoven.

Tim Bray
Read my blog.

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Postscript

How I found this: I was reading this post by Jeff Atwood, titled "Linus Torvalds, Visual Basic Fan" where the source article he linked to was: "STIFF ASKS, GREAT PROGRAMMERS ANSWER". But that link was dead, and doing a search didn't find any trace of it anywhere on the net. So I resorted to an archive.org search and sure enough, up popped this incredible blog post by Jaroslaw Rzeszótko.

Due to it no longer being available on the net, I thought it should reposted again so others can enjoy reading it. I requested permission from the original author to do this, and he happily obliged - thanks again Jaroslaw!

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Read a Chinese translation of this blog post  << Thanks to the guys at CoolShell.cn for this!

Read a Turkish translation of this blog post  << Thanks to Seval for this!

Startups for Dummies

The problem with Steve Blank’s How to Build a Web Startup (Lean Launchpad Edition) article ...

There’s little to no focus on the actual product being built.

Only 1 out of 50 points listed is actually about building a product: Its listed under step 7, which is: “Add the backend code to make the site work”.

The rest is mostly cruft and admin type work that an outsourced worker could do. No doubt its important, but 98% compared to 2%?

The article comes across as a guide to building an over-hyped marketing vehicle, solely to receive funding, rather than actually building something useful that people want to use. There’s no mention of innovation or of making people’s lives easier. This is Startups For Dummies.

Full respect to Steve Blank (a 34 year veteran of Silicon Valley) and his views, but in my view, this particular article has a glaring weakness.


Some further reading on the topic:

This Starting a Startup article by Paul Graham is simple but contains three great points he says you should focus on:

• People/a good team
• A product that customers want
• Low overheads

This 12 Ways To Make Your Web Startup Investable article by StartupSmart, recommends:

• People/a good team
• A clear market gap (i.e. a product that customers want)
• Timing is everything

Incidentally, Steve Blank has just announced he is giving a free online course over at Udacity - Entrepreneurship: The Lean Lanchpad (EP245). It starts on 14 September, 2012.


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TCP/IP Sockets in .NET 4

TCP is one of the core protocols of the Internet and is a bi-directional, client/server protocol. In .NET you can use the TcpListener Class for the server component, which provides simple methods that listen for and accept incoming connection requests from clients. You can use the TcpClient Class for the client component, which provides client connections to TCP server components; it provides simple methods for connecting, sending, and receiving stream-based data over the network.

Here's a standalone C# 4.0 app that demonstrates how to setup a TCP/IP sockets based client and server in .NET. It uses a command line option to determine whether to run the client or server. There's no external files or libraries needed, just the standard ones you get with a C# 4.0 console project. I've tested it with Visual Studio 2010 in Windows, and it will also work unchanged with Mono.

To run the server, from the command prompt...
   SocketsTest -server

To run the client, from another command prompt ...
   SocketsTest -client

Below is the source code ...

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Threading.Tasks;

/// 

/// Standalone TCP/IP sockets example using C#.NET 4.0
/// 
/// 
/// Compile as a C#.NET console mode application
/// 
/// Command line usage:
///   SocketsTest -client   => run the client
///   SocketsTest -server   => run the server
/// 
class SocketsTest
{
    static TcpListener listener;

    // Sample high score table data
    static Dictionary<string, int> highScoreTable = new Dictionary<string, int>() { 
            { "john", 1001 }, 
            { "ann", 1350 }, 
            { "bob", 1200 }, 
            { "roxy", 1199 } 
    };

    static int Port = 4321;
    static IPAddress IP_ADDRESS = new IPAddress(new byte[] { 127, 0, 0, 1 });
    static string HOSTNAME = "127.0.0.1";
    static int MAX_CLIENTS = 5;

    public static void Main(string[] args)
    {
        if (args.Contains("-server"))
        {
            ServerMain();
        }
        else if (args.Contains("-client"))
        {
            ClientMain();
        }
        else
        {
            Console.WriteLine("Usage: SocketsTest -client   => run the client");
            Console.WriteLine("       SocketsTest -server   => run the server");
        }
    }

    /// 

    /// Server receives player name requests from the client and responds with the score.
    /// 
    private static void ServerMain()
    {
        listener = new TcpListener(IP_ADDRESS, Port);
        listener.Start();
        Console.WriteLine("Server running, listening to port " + Port + " at " + IP_ADDRESS);
        Console.WriteLine("Hit Ctrl-C to exit");
        var tasks = new List();
        for (int i = 0; i < MAX_CLIENTS; i++)
        {
            Task task = new Task(Service, TaskCreationOptions.LongRunning);
            task.Start();
            tasks.Add(task);
        }
        Task.WaitAll(tasks.ToArray());
        listener.Stop();
    }

    private static void Service()
    {
        while (true)
        {
            Socket socket = listener.AcceptSocket();

            Console.WriteLine("Connected: {0}", socket.RemoteEndPoint);
            try
            {
                // Open the stream
                Stream stream = new NetworkStream(socket);
                StreamReader sr = new StreamReader(stream);
                StreamWriter sw = new StreamWriter(stream);
                sw.AutoFlush = true;

                sw.WriteLine("{0} stats available", highScoreTable.Count);
                while (true)
                {
                    // Read name from client
                    string name = sr.ReadLine();
                    if (name == "" || name == null) break;

                    // Write score to client
                    if (highScoreTable.ContainsKey(name))
                        sw.WriteLine(highScoreTable[name]);
                    else
                        sw.WriteLine("Player '" + name + "' was not found.");

                }
                stream.Close();
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
            }

            Console.WriteLine("Disconnected: {0}", socket.RemoteEndPoint);
            socket.Close();
        }
    }

    /// 

    /// Client requests a player name's score from the server.
    /// 
    private static void ClientMain()
    {
        TcpClient client = new TcpClient(HOSTNAME, Port);
        try
        {
            // Open the stream
            Stream stream = client.GetStream();
            StreamReader sr = new StreamReader(stream);
            StreamWriter sw = new StreamWriter(stream);
            sw.AutoFlush = true;

            // Read and output the first line from the service, which
            // contains the number of players listed in the table.
            Console.WriteLine(sr.ReadLine());

            while (true)
            {
                // Input player name
                Console.Write("Enter player name: ");
                string name = Console.ReadLine();

                // Write name to server
                sw.WriteLine(name);
                if (name == "") break;

                // Read score from server
                Console.WriteLine(sr.ReadLine());
            }
            stream.Close();
        }
        finally
        {
            // Close the connection
            client.Close();
        }
    }
}

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EMPORI: The original Amazon Locker from 12 years ago

Amazon Locker is a new delivery option offered by Amazon which provides secure, self-service pick-up stations located in a select number of cities in the US and UK. Once your package is delivered to the Amazon Locker, you receive an e-mail informing you that your package is available for pick-up.

This Amazon service came about 1 year after a Canadian startup called BufferBox started offering a similar secure dropbox service. BufferBox has lockers installed in two locations in Waterloo, one at the university and another a nearby corporate office. The company is nearing a launch in Toronto and plans to roll out lockers across Canadian and U.S. cities.

But back in 2000, another Canadian company launched a similar service. On July 24, 2000, Canadian property management company Oxford Properties Group launched a startup called EMPORI.COM. Customers could order products from affiliated online retailers via  Empori.com, which were then delivered on the same or next day to a secure depot containing lockers. The original depot was located in an office building in Toronto (Royal Bank Plaza) and over the course of a year this expanded to three more sites around Toronto. Oxford Properties Group saw this as a way for their commercial real estate customers to get additional value out of their prime inner city locations. The idea was that city workers would order products online and then, after receiving an email notification with the locker location and locker combination, would pick their order up at the end of the day, on their way home from work. A host of a products from 31 vendors were offered, from books to running shoes to groceries and even liquor.

The upmarket secure lockers offered by Empori

From the launch press release: "Empori.com is the one-of-a-kind retail solution to those barriers that discourage people from purchasing online. Our delivery system addresses the online shopping fulfillment problem."

Less than 1 year later, on July 17, 2001,  Empori.com closed after a $5 million loss. The blame was initially placed on the general business environment which included the bursting of the dot com bubble: "With recent changes in the dot-com environment, [Empori] was unable to find another strategic and financial partner to support further development of the business-to-consumer business,"

As the dust settled it looked like the single biggest factor in Empori’s failure was its inability to secure a critical mass of online retailers.  They tried to do too much - secure depots for pick-up was only one piece of their ambitious plan - they were also reselling goods via their website, which was the sole point of contact to access their secure depots. In effect they were trying to launch a new online retail site, coming off a base of zero customers, while in the general dot com gloom of 2000/01. Maybe what they should have done is to focus solely on their unique selling point - the secure depot - and offered it as a service, available to any online retailer, much as BufferBox is doing today.

The business burned $5 million in one year before closing

As of today, the Empori.com domain name is offered for outright sale for €3540 ($4351) by a European domain reseller. "Empori" is Italian for "Stores".

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Old school developers - achieving a lot with little

Ken Thompson

I was reading through bits of the excellent Coders at Work book by Peter Seibel and found it interesting that the (what I'd call respectfully) old school developers, such as Ken Thompson, Joe Armstrong and Jamie Zawinski use hardly any modern tools and techniques while developing software.

Ken Thompson was the designer of the B programming language (the precursor to C) and also the Go programming language (with Rob Pike). He also worked alongside Dennis Ritchie to develop the C programming language and the original Unix operating system while working at Bell Labs. After designing the UTF-8 method of character encoding on a placemat in a New Jersey diner, he worked overnight to implement full UTF-8 support in Bell Lab's Plan 9 operating system. Regarding his programming style, he debugs only via printf statements, hardly ever uses unit tests, starts his projects by designing the data structures and then works bottom up, with throwaway test stubs.

Joe Armstrong

Joe Armstrong developed the Erlang programming language and the open source Open Telecom Platform (OTP) framework for Ericsson. When designing software he prefers to rigorously document as much as possible up front before starting to write code, especially for difficult projects such as those involving real-time networking protocols. He uses prototypes to solve the hard problems first, and for debugging, just uses print statements. He is a critic of Object Oriented Programming, and favours functional programming languages like Haskell. He never uses an IDE, preferring just Emacs and the command line (no mouse required).

Jamie Zawinski worked in MIT's AI lab with Lisp, then moved onto leading the development of Lucid Emacs, also in Lisp, which later became known as XEmacs. After this he joined Netscape and worked on the front-end for the Unix version of Netscape Navigator, and later led the development of Netscape Mail (both projects were in C). He too prefers to just use print statements to debug his code. His process is either to write code top down or bottom up, let the code evolve naturally, then refactor it when necessary. During development he hardly ever uses unit tests, believing it slows things down - he thinks there's a lot to be said for getting the code right first time. In his view, its a matter of priorities, "do you want this to be good software or do you want it to be done next week - pick one because you can't have both".

Jamie Zawinski

So what tools and techniques do you actually need to be a great programmer? Are these modern techniques of TDD, BDD, Scrum, Agile, Design Patterns, XP etc. just window dressing or do they serve a higher purpose? Is it just a fact that a gifted programmer will always find a way to be a great programmer, no matter what tools he or she works with?

My own view is that some level of TDD and a reliance upon a decent set of unit tests is invaluable. Maybe then these modern techniques should just be seen as advances to make our job a little easier and more productive, especially for those who are not a genius-level developer, like these guys.

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Being a great tester

I just wanted to post a great little nugget of information from the end of Unit 1 of Software Testing: How to Make Software Fail (CS258) on Udacity, which is being taught by John Regehr and Sean Bennett.

• The developer's attitude is "I want the code to succeed".
• The tester's attitude is "I want the code to fail".
• Although they seem contradictory, understand that you are both aiming to create more robust, higher quality software.
• The developer aims to write quality code first time.
• The tester aims to identify bugs which can then be fixed, thereby improving the robustness of the code.

Great testers ...

• Test creatively - use their knowledge of the software under test to be creative in their test methods and test structure.
• Don't ignore small glitches that are easy to overlook or ignore, but may hint at larger problems, which when followed up can often lead to major issues.

Watch the snippet on YouTube: Being a great tester (2 min, 33 sec)

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Applying hardware testing concepts to software

I've recently been testing a desktop application I built with WPF and .NET 4 which collects data from the serial port and draws various charts on screen in real time. The volume of data isn't immense, one data frame of approx 200 bytes arriving every 200 milliseconds, but there is additional processing happening in the background. One of the steps being performed is regression analysis on various data points to construct curves of best fit.

In production this process will be run for likely not more than 30 minutes, but during testing I wanted to test the limits of the application by running the process for 2 hours, to be sure there was no memory leaks or performance issues. I was surprised when after just 1 hour the UI just became totally unresponsive, dramatically quickly.

I did find the issue and made the fix, but this got me thinking about where else this sort of issue could occur in software - because all I'd done was apply a simple form of software performance testing, known as endurance testing, which just involved running the software for significantly longer than normal. The endurance test has something in common with its hardware equivalent, soak testing.

The bathtub curve. The name derives from the cross-sectional shape of a bathtub. Image source: wikipedia

This leads to another hardware concept which I think can be partially applied to software - the bathtub curve, as shown above. The bathtub curve is used in reliability engineering to describe a particular form of the hazard function which comprises three parts.

Applied to hardware, the bathtub curve means:

1. The first part is a decreasing failure rate, known as early failures. Burn in testing aims to detect (and discard) products which fail at this stage. If the burn-in period is made sufficiently long (and artificially stressful), the system can then be trusted to be mostly free of further early failures once the burn-in test is complete.
2. The second part is a constant failure rate, known as random failures. These are like the "background" level of failures, which can usually never be totally eliminated from the production process. QC managers will often aim for a low level of failure here, via various quality control measures (such as TQM or Six Sigma).
3. The third part is an increasing failure rate, known as wear-out failures. These can be detected via soak testing.  In electronics, soak testing involves testing a system up to or above its maximum ratings for a long period of time. Often, a soak test can continue for months, while also applying additional stresses like extreme temperatures and/or pressures, depending on the intended environment. 

Applied to software, the bathtub curve might show bug count on the y-axis and total application run-time on the x-axis. Then, the three parts could mean:

1. First part (early failures): In software, this could apply to bugs which break the software's functional requirements or specifications, and might be tested with various functional testing methods such as unit testing or integration testing. These are normally found early in the test cycle.
2. Second part (random failures): Might apply to random bugs which are hard to detect, occur in specific conditions, and are outside the existing test coverage. An example might be a heisenbug. 
3. Third part (wear-out failures): Bugs which appear due to memory leaks or performance degredation. These can be tested with endurance testing. During endurance tests, memory utilization is monitored to detect potential memory leaks, and throughput/response times are monitored to detect performance degradation.

Further Reading

Since writing the above I've found some other articles (listed below) about this concept which assume time on the bathtub curve to mean the software development life cycle's time, as opposed to my idea of being the individual run-time of a real-time application. I've listed them here for reference:

The bathtub curve for software reliability
Does the bathtub curve apply to modern software?
The Software Bathtub Curve
Improving Software Reliability using Software Engineering Approach - A Review



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