Got me - I was thinking of HDDs which from the beginning had at least 2 heads so, given an appropriately sized Gap1, it was always faster to switch heads. And FWIW is some later SyQuest cartridge drives employing sectored servos it was faster to seek than to switch heads so they made a head switch into a seek, but they masked that all in the drive firmware
In any event, it really doesn't matter for this device emulator if the end of a track is followed by a seek command; any time there is a seek command there is lots of time for the device's housekeeping to get ready for the next read. Tom -----Original Message----- From: Fred Cisin [mailto:ci...@xenosoft.com] Sent: Wednesday, April 20, 2022 11:55 AM To: General Discussion: On-Topic and Off-Topic Posts Subject: RE: idea for a universal disk interface On Wed, 20 Apr 2022, Tom Gardner via cctalk wrote: > Likewise, I don't know it for certain, but I am pretty sure that it is > true that virtually all controllers switch heads sequentially when > transferring blocks beyond the end of the track, Are you implying that data/file that is more than one track long has its next data on a track that is a different head of the same cylinder? If that is, indeed what you are saying, . . . It would make sense, and is common. Since it is obvious that switching heads should take less time than stepping to the next cylinder. BUT, it is a choice by the file system, not by the controller. As a simple example, when floppy disks went from single sided to double sided, SOME OS programmers chose to switch heads before stepping to the next cylinder. (Cylinder 0 side A, cylinder 0 side B, Cylinder 1 side A, cylinder 1 side B, etc.) BUT, some chose to "keep what they had", and use the second side as an "extension" of the first side, and chose to not switch heads until all tracks on the first side were exhausted. (Cylinder 0 side A, Cylinder 1 side A, Cylinder 2 side A . . . ) Of those, most "recalibrated" (seek to zero) for the second side (cylinder 0 side A, Cylinder 1 side A . . . Cylinder 75 side A, Cylinder 76 side A, Cylinde 0 side B, Cylinder 1 side B) (that's for 77 track 8") while others started using the second side starting at the high end (to avoid the seek to zero delay). (cylinder 0 side A, Cylinder 1 side A . . . Cylinder 75 side A, Cylinder 76 side A, Cylinder 76 side B, cylinder 75 side B, . . .) There were a few more variations, because it was the programmer making the decision, not the controller, and we can come up with some amazing cockamamy ideas. -- Grumpy Ol' Fred ci...@xenosoft.com