Terminal paging in the kernel - (nf)

Fri Mar 16 22:05:57 AEST 1984

#R:cca:-684100:fortune:11600071:000:1092
fortune!rpw3    Mar 16 01:53:00 1984

I agree with Steve Zimmerman -- paging in the kernel with parameter-setting
in "stty". Notice that this obeys the VERY IMPORTANT software design
principle called "separation of policy and mechanism". Here, "stty" sets
policy, all the kernel does is implement it.

Other examples: operating systems which put only a low-level process switcher
in the kernel and put the long-term scheduler and swapper in user mode; network
protocols which put the data moving in the kernel but put session control in
user mode; systems which put the magtape driver in the kernel but all of the
label handling and volume switching in user mode; error-flagging vs. error-
logging and reporting; process accounting vs. logging and reporting; etc, etc.

The key is that as long as the mechanism is clean (and general) enough, one
can implement many policies on it. How many different UNIX shells have there
been? They all use "fork" and "exec".

Rob Warnock

UUCP:	{sri-unix,amd70,hpda,harpo,ihnp4,allegra}!fortune!rpw3
DDD:	(415)595-8444
USPS:	Fortune Systems Corp, 101 Twin Dolphin Drive, Redwood City, CA 94065