80-Bus News


Summer 1985, Volume 4, Issue 2

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configuration file is edited with a text editor to suit the drive configuration required, and the whole lot put together with GENSYS which goes to the BIOS file and pulls out the bits it wants. GENSYS then gives you the option of putting the results on to a system track or saving it as a file for use with SYSGEN later. The attraction from Gemini’s point of view is that when significant changes have been made to the BIOS or new permutations of drive and format take effect, all they have to do is issue new versions of BIOSx.SYS and everyone can reap the benefit without all the hassle of having to send disks back to Gemini for upgrade.

So what does BIOS 3.2 offer? Apart from all the drive permutation twiddles, basically all the normal Gemini features, screen editing, screen dump, etc. Also the usual I/O byte support for serial and parallel printers, serial transmission protocols and all the rest. Nothing radically new, just the latest versions with extensions to the patch area so that all three different IVC/SVC cursor types may be defined, and screen edit mode may now be disabled.

The fun really starts around the drives. If BIOSFW or BIOSW for winnies is included, then the winnie can be partitioned as required, for instance you could make five 1M drives out of 5M winnie (I can’t think why you should want to, but you can) or, more usefully, for example an 8M and a 2M out of a 10M winnie (8M being the maximum CP/M 2.2 can address).

The permutations of drives can be fun, one problem with SYS was that you couldn’t easily mix drive types beyond 5″ 48 tpi with 8″, or 5″ 96 tpi with 8″. So mixtures of 48 tpi and 96 tpi were out as you couldn’t make SYS double step 96 tpi drives to read 48 tpi formats. With BIOS 3.2 you can. The menu is impressive for home use, yet not powerful enough to make any competition to Gemini’s own MFB series of machines. All the past and present Gemini formats are supported, naturally, that’s both 96 and 48 tpi double density and the original double sided single sided GM805 format. Additionally, Superbrain 48 tpi single sided, IBM PC 48 tpi single and double sided 8 sector formats, DEC Rainbow, both Nascom formats and dear old fashioned 8″ single sided single density. What’s more you can assign more than one logical drive assignment to one physical drive. So for a person like me who gets a lot of disks in various Gemini formats, the following works a treat.

Logical Drive A:Gemini 5M winnie
Logical Drive B:Gemini QDDSPhysical drive 0
Logical Drive C:Gemini QDDSPhysical drive 1
Logical Drive D:Gemini DDDSPhysical drive 1
Logical Drive E:Gemini SDDSPhysical drive 1

By sticking disks in either drive 0 or drive 1 as appropriate, I can copy anything that comes my way to either the other drive or the winnie. Similarly, if people expect things returned, I can copy stuff back to their original disks with no problem. The only problem comes when formatting disks, BIOS 3.2 does not supply a format program which will pick up the disk dph’s and format to the standard in current use by the drive. Pity that, I’d have loved to have sent this disk to Paul in say DEC Rainbow format and then see how long it would take him to sus what I’d done. Never mind, I’ll invent a wierd format of my own using ALLDISC, that should fox him completely and give Gemini’s new MFB2 something to get upset over.

BIOS 3.2 is even more intelligent than it already appears. Lets take an instance where you are using a 96 tpi machine to construct a system track for a 48 tpi machine. It wouldn’t be a lot of good if the result sent to disk was 96 tpi, as the 48 tpi drives couldn’t read it. No if the BIOS constructed is a 48 tpi BIOS, then GENSYS will write the result to either a 48 tpi drive or double step (still equalling 48 tpi) to a 96 tpi drive, the boot sector being correctly set up for the 48 tpi format. This brings me to the second big feature of BIOS 3.2. Each physical drive can be specified separately. One drive could be an 8″ for instance, another, a double sided 96 tpi with 3ms head stepping and no head load delays, another, a 96 tpi single sided with 20mS head stepping and 50mS head load delay and spectacularly long head settle times, whilst yet another drive could be a double sided 48 tpi drive with 10mS head stepping and no head delays. A maximum of four physical drive may be specified by type 8″ or 5″, the number of tracks per inch, the number of tracks. the number of sides, the step, head settle and load times.

BIOS 3.2 expects you to be logical about your logical to physical drive assignments, it no good specifying 96 tpi formats to a 48 tpi drive for instance, on the other hand it a 48 tpi format is specified to a 96 tpi drive, then the drive is forced to double step to read and write like a 48 tpi.

Reading 48 tpi disks with a 96 tpi drive works well, writing needs care, as the disk should be wiped clean with a magnet and reformatted using the 96 tpi drive before data is written, using the 96 tpi drive (hence the need for the format program). This is because the heads of a 48 tpi drive are wider than those of a 96 tpi drive and therefore track a wider area. If a disk previously written using a 48 tpi drive is rewritten using a 96 tpi drive, there will be areas of the original 48 tpi recording left between the tracks recorded by the double stepping 96 tpi drive. When the disk is placed in the 48 tpi drive, the head will track both the intended track recorded by the 96 tpi drive, and also the residual crud left from the original 48 tpi recording. This will degrade the signal to noise ratio, often to the degree that the disk can not be read.

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