> My understanding is that HZ=100 was a practical choice because the > machines of the day could not reliably drive a faster clock interrupt.
The VAX architecture defines a 100Hz timer, which is the only timer you can be sure will be available to the kernel. A few of the later models (VAXstation 4000 comes to mind) have a so-called diagnostic timer with a better precision. Thus when BSD was ported to VAX, there was no choice but have HZ=100. And when it was ported to other platforms (such as hp300), that value was kept because there was no good reason to change it. The value of hz became adjustable because some hardware came with clocks which required a power-of-two divider, such as the 4.4BSD pmax port which had HZ=64. And of course, later, alpha was architected to have a 1024Hz timer, so HZ=1024 on these systems as well.
