R: R: Floppy disk: one drive per face

First of all I would like to thank you all for every suggestion that comes The z80 based machine was called GENERAL PROCESSOR Model T year 1981. You can see it here: https://www.vintagesbc.it/?page_id=877 and the cards it was equipped with here: https://www.vintagesbc.it/?page_id=879 even if it is old information because I, together with a competent hardware technician and another enthusiast who has already written an emulator HERE: https://nippur72.github.io/gpmodelt-emu/ (you have to press CR to start then BD and enter ...) and the emulator video here: https://www.youtube.com/watch?v=cRmmUYkaDxs&feature=youtu.be we are proceeding to derive electrical schematics, save firmware, software, and try to reconstruct and document everything. You have to think that they used a WD1791 which has an inverted data bus and in the firmware they use CPL instruction to invert it again so on the disk the CP / M (CCP + BDOS + bios) is written all INVERTed. Based on the firmware on eprom configuration it could manage: - 2 drives 8 "(128x26x77) or 5" (128x18 (maybe 16) x40) all in FM and seen as A, b, c, d - 1 8 "DSDD single B unit and 1 HD 10MB Winchester drive (divided into 2 halves A and C) At the beginning the engineers made ibm 3740 in side A. Only after they passed to make a drive double face so we think they didn't change things also because it seems to be possible to boot from both side A and side B and we expect the side B of drive A it would in IBM 3740 format. We noticed that the sectors always start from ZERO and not from 1 so it is interesting what you say: ?you really should try unplugging the heads of the drive and swapping them. That will put "side A / 0" on the second / B side of the disk.! " Enrico -----Messaggio originale----- Da: cctalk [mailto:cctalk-bounces at classiccmp.org] Per conto di Fred Cisin via cctalk Inviato: venerd? 6 novembre 2020 20:41 A: General Discussion: On-Topic and Off-Topic Posts Oggetto: Re: R: Floppy disk: one drive per face On Fri, 6 Nov 2020, Enrico email.it via cctalk wrote: WRITE PROTECT ALL OF THOSE DISKS, BEFORE YOU START! Can you tell us the NAME of the machine? (Unless the NAME is "1981 Italian Z80") WHAT SIZE disk is it? Is it 26 128 byte sectors, or is it 10 256 byte sectors? 35, 40, 70, 77, or 80 cylinders/tracks? What kind of drive? 3"? 3.25"? 3.5"? ((8" 26 * 128 * 77) is not the same as (5.25" 10 * 256 * 80)) Yes, a 5.25" SSSD disk CAN hold 18 128 byte sector per track, but you might have to squeeze the [inter-sector] gaps a little, so 16 may be a more conservative choice. In the sector headers, . . . On the second side, is the "HEAD NUMBER" field, in the C/H/R/N sector headers, 0? or 1? If 0, then you really should try unplugging the heads of the drive and swapping them. That will put "side A/0" on the second/B side of the disk. If the "HEAD NUMBER" field, in the C/H/R/N sector headers, is 1 Then you are best off doing as Chuck suggested, and LYING to the transfer program to tell it that it is a format that goes UP the first side, then retracts to track 0 and then goes UP the second side, (there were numerous formats that did that) but that you want the transfer program to IGNORE the first half of each disk ("side A"). Ignoring the first half in that case can be done on a CP/M disk by saying that the number of "RESERVED TRACKS" (system tracks to be ignored for data transfer) includes the entire first side, and the first few of the second side. If you can image the disk with a DOCUMENTED image structure, then consider writing some trivial code to split the image, to give you separate images of the two sides, and then try to read the files from each of those, as if they were two single sided drives. Or, write a disk copy program to read the second side, and copy it to the first side of a scratch disk. BTW, the "each side is a separate drive" patches for PC-DOS 1.00 were 8 512 byte sectors on each side, with 40 tracks, so those would not help. Yes, we're all bozos on this bus. ("Firesign Theater" fourth album) But, when it comes to disk formats, none of the rest of us bozos can compare to Chuck. BTW, in cultures that frown on stealing sheep, that is sometimes expressed as "teaching grandma to suck eggs". -- Grumpy Ol' Fred Cisin cisin at xenosoft.com XenoSoft http://www.xenosoft.com