magic number 7 [LWN.net]

magic number 7

Posted Jun 8, 2011 15:44 UTC (Wed) by giraffedata (subscriber, #1954)
In reply to: A conversation with Linus at LinuxCon Japan by nye
Parent article: A conversation with Linus at LinuxCon Japan

(PS. The idea in question is, of course, utter bollocks. For supporting evidence, see the 3 billion people who happily memorise lots of 11-digit telephone numbers, for example)

I think you missed the point. Few of those people could repeat a random 11 digit number you say slowly back to you. The 7 limit is working memory -- where things stay in your brain before they are memorized. Also, many people could repeat back an 11 digit telephone number because it contains multi-digit chunks which are a single piece of information. For example, a North American area code is 3 digits, but in most cases, that would count 1 toward the limit.

Incidentally, as the Wikipedia article admits, current thinking is that the real number is less than the 7 +/- 2 from the 1950s research.

If there were some reason that people needed to think about some feature of all minor releases of a certain major release of the kernel at once, then 20 would be way too many. But I think marcH was just making a light-hearted comment about a number being intrinsically too big. It's pretty clear that the only thing 20 is too big for is some aesthetic feeling Linus has about normal looking release numbers.

(Log in to post comments)

magic number 7

Posted Jun 8, 2011 23:04 UTC (Wed) by neilbrown (subscriber, #359) [Link]

I don't know what Linus' problem is, but the problem I have with big version numbers is that the differences become too small - I lose track of where we are up to.

The difference between 38 and 39 is simply a lot smaller than the difference between 8 and 9 (is some cognitive sense which I believe psychologist can measure) and I have trouble remembering which of those two is 'next'.

It felt really good when 2.6.39 was done because then the "next" version would be 2.6.40, and the difference between 40 and 39 is MUCH bigger than the difference between 39 and 38. And then 2.6.42 wasn't far away and the difference between 42 and any other number is clearly very big too. So we were coming to a time when I would not be confused about version numbers for at least a year or so.

So it seemed like a strange time to change numberings, just when the up coming numbers would be so much easier to work with. But I definitely understand how numbers can be "too big" - it is when their differentiation becomes too small.