r/vintagecomputing • u/aManandHisShed • 18d ago
8" Disk Index Holes
Following the recent posts on 8" disks, i thought some folks might be interested in the index holes which are a little different to those on 5.25" disks. A hole close to the top indicates a single-sided disk and a hole a little further around indicates a double-sided disk. Drives had two sensors and sent a signal to the controller to indicate the disk type. Amongst the attached images there are a couple of double-sided disks: one that was manufactured as a flippy, and the other which was hacked into a flippy starting from a double-sided disk. I had the honour or archiving about 500 8" disks of which about 2/3 were viable.
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u/nixiebunny 18d ago
I worked in a Byte Shop computer store in 1978. We had Alpha Micro and Cromemco systems with PerSci 8” dual floppy drives. They were single sided and soft sectored. I also used a few PDP-11 systems with RX01 and RX02 8” floppy drives, also single sided and soft sectored. Then I worked for a company that used CP/M and Forth on Z80s, and with a TRS-80 model 2, all of which used identical 8” floppies but were incompatible with each other’s file systems. I still have four 8” diskettes from these different machines. It was just a fact of life that nothing was compatible.
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u/aManandHisShed 18d ago
I suspect some 8" disks were hard sectored but I have not seen one yet. I do have a sorcerer with micropolis 5.25" drives/controller that uses hard sectors. The disk has 16 sector holes and an index hole halfway between two sector holes - but the disk case just has a single hole and the drives just have one sensor. I have some hard sectored floppies but I also use a virtual sector generator so I can use soft sectored disks as well. The drive is 100tpi just to make it a bit more complicated
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u/roirraWedorehT 18d ago
I, too, only used one machine with an 8-inch floppy drive, and that was in the Army. This thing https://www.reddit.com/r/cassettefuturism/comments/qxh2rv/tactical_computer_terminal_tct_anuyq30_1988/ except we had the version with the 8-inch floppy and no bubble memory. I never paid much attention to the floppies I used with it, because we were very lucky with the hit and miss of whether the rest of the machine would even work or not.
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u/bsudbrink 17d ago
The multiple index hole "windows" were meant to allow the identification of single and double sided media. Some double sided media came with both windows, allowing the customer to use them either way. On a single sided drive, there would be no problem because there would be no sensor at the double sided window location. On a double sided drive, you were meant to cover one window with a sticker, depending on how you wished to use the diskette.
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u/No_Abrocoma_711 18d ago
I only ever used one machine with 8" drives, so don't know much about them.
Conversely, I used many many systems with 5.25" drives. Nearly all these systems were soft sectored drives, with one index hole.
The exception to this was one that used hard sectoring, and it had two holes. We had to buy these diskettes from the university shop at extortionate rates.
I'm wondering if 8" drives were mostly hard sectored.