DEC machines that can't format a disk (Was: Good Trip/Score Dec

From: Rick Murphy <rmurphy_at_itm-inst.com>
Date: Mon May 20 20:37:40 2002

At 09:09 PM 5/20/02 -0400, Jerome H. Fine wrote:
>Just in case you forgot, what might the extra cost of an RL01/RL02
>drive have been that could do the FORMAT command?

Well, one problem with the RL01/RL02 was that the drive did not have the
ability to seek to an absolute track. To get to a particular track, the
controller/disk driver first had to read the servo information to figure
out what track the drive was on, then seek the heads in the proper
direction and offset to get to the target track. THEN the driver had to
read another sector header to make sure the drive actually got there. (I
once worked an RT11 driver bug that caused a system hang; this was caused
by the heads wandering off track; the driver, "knowing" that the heads were
already on the right track, didn't re-issue a seek.)

Given the simplicity of the drive hardware - it *had* to have a servo track
to position itself - there's no surprise it couldn't low-level format. Sort
of like most modern disk drives - but you can probably buy a 50 GB IDE
drive today for the cost of one RL01 cartridge back then :-(
         -Rick
Received on Mon May 20 2002 - 20:37:40 BST