Terminal paging in the kernel

[phil%rice at sri-unix.UUCP]

From:  William LeFebvre <phil at rice>

	Yea, and *we* make assumptions about what disk drives are.  In a piece
	of common code.  That it's 24 sectors around and maybe 80 tracks
	deep.  Is there not a trend toward larger disks, or controllers with
	built-in addressing smarts?  We change the kernel code again and
	again...

Given a typical system, there are a wider variety of terminals than
disk drives.  Mainly because there are about 20 times more terminals on
the system than disk drives.  Also, given a typical system, terminal
types tend to change more often than disk drive types.  Mainly because
there is an order of magnitude complexity difference between changing a
terminal and changing a disk drive.  Not to mention the fact that
people who dial up a computer use whatever terminal they have at home.
When was the last time you changed the type of drive you are using?
When was the last time you added or swapped out a terminal?  When was
the last time someone connected a disk drive to your system over a
phone?  Your argument is fairly vacuous.  It's quite true that the disk
drive characteristics are hard coded in the kernel.  But they don't
change very often.  You can afford to hard code disk drive
characteristics.  I'm not saying it's a good idea, but you can get away
with it.  You CAN'T afford to do that with terminals!  And anyone that
does so is painting himself into a corner.

                                William LeFebvre
				Department of Mathematical Sciences
				Rice University
                                <phil at rice>