A computer deals with interrupts all the time. They are the mechanism by which it can simulate multi-tasking among many different programs in a modern operating system. However those interruptions have a price, and too many of them can affect performance. As hardware grows larger, we have other issues from interruptions that we try to mitigate with techniques like soft-NUMA affinity or multiple pipelines built into hardware. All of these are designed to prevent a computer from spending any significant time on non-productive tasks because of interruptions.
In the real world, many of us deal with regular interruptions from work. They might be emails, instant messages, phone calls on a cell phone, or the old fashioned someone-stopping-by-your cube-to-chat. All of these things add up to less productivity, especially for developers. One study finds a 10 point IQ drop from regular email and phone interruptions. I don’t know about you, but I’m not sure I can afford a 10 pt drop in IQ when I’m working.
Some companies are starting to realize that developer’s brains are a scarce resource, andinterrupting them can dramatically impact productivity. I have found some places, like this one, that are setting aside quiet time for developers to work without being bothered. Similar to the technical debt that Steve McConnell has talked about, there seems to be an interruption tax that some development shops are loathe to pay.
Even if you don’t gain any productivity, or have fewer bugs, or ship more often, I think that your developers will appreciate it. It could be an easy way to increase happiness, improve retention, and even sell your company as a good place to work. And it’s easy to implement: just leave people alone a few hours a day.