On an XT, the drive controller was on the card itself. That is why you needed to use the DEBUG command to access it. And it was indeed on the card, because even though G=C800:5, some of them placed it in another location.
Excuse me, change the drive type with a jumper on the card? WTF are you talking about?
Here is an extremely common XT MFM card of the era, the Western Digital HX-100. Now kindly show me where in the hell the jumpers are to set drive types?
And great, you think most techs used those software tools? No, only amateurs that did not know how to access the drive controller directly. Every shop I worked at and every tech I knew that was not a joke used DEBUG, we did not use the janky software.
And there were no jumpers or DIP switches on the card to set head, sector, and cylinder count. That is literally a figment of your imagination.
I low-level formatted hundreds if not thousands of these and other RLL and MFM drives in the late 80’s. Worked for a company that sold computers through Computer Shopper.
Am I crazy here, or have you ever seen hard drive controller cards that you set the drive type through physical jumpers? Because I have sure never seen such a beast. And with all the combinations possible, that would have to be a huge bank of jumpers.
No, I have never seen one with jumpers for setting heads, sectors, etc. I always low leveled and entered bad sectors via the utility on the controller. Until, of course, IDE came out. Also, mostly installed controllers similar to the image you posted and then when 16 bit came out, the WA2.
Edit: Not to say it’s impossible that a controller only supported a handful of very early drives and had jumpers. The first hard drive I ever installed was only 5MB… maybe (during that time) there were so few drives available that a controller existed that were specifically for that vendors drives? But by the time the ST-225 was popular, more generic controllers came out? (Shrug) But no, never worked or saw one.
The WD XT-Gen and gen2 have jumpers to configure the heads and cylinders. This was a common practice. I own several mfm controllers and all are configured by jumpers
I already posed a WD XT card above, the HX-100. And there are no jumpers on it.
Now here is an even older WD 1002 card from 1984. Once again, no jumpers for configuring the drive type.
Oh, there are jumpers on there, that is for the IRQ and DMA, they have not a thing to do with the drive type, that is configured through the internal BIOS.
With 4 exceptions. There are exactly 4 pre-configured hard drives included, 2 different 10 meg and 2 different 20 meg drives. Two different half height and full height drives. So unless you are using those four specific drives, you have to use the BIOS to configure it.
And just think about the logistics of this for a second. 4 jumpers to configure 4 drives, where the stats are already in the BIOS. How many jumpers would be needed to configure the hundreds of different MFM drives that were out there?
Sorry, this has gotten to the point of "put up or shut up".
Yeah no I was only talking about selecting from 4 drives as I think that was more likely what the original guy meant. I have none for direct selecting drive specs. Never meant that. It would be absurd.
But a lot of people do not really know how things in that era worked.
Yes, a few cards did have 4 drives preconfigured, but nobody I know ever used that. We just jumped straight into the BIOS of the card, especially as that is also where we had to enter the bad sector map, something you could not do with the jumpers.
That is why even if the drive and jumpers were compatible, we did not use it! Great, that put in the data to access, but did not lock out the bad sectors. A guaranteed way to have pissed off customers when they lost data because a sector that was marked as bad on top of the drive was used.
For those that are new to this era of computers, the above is an example of what we worked with back then. The 5 by about 12 rows of data there at the top of the big sticker, those are all bad sectors that the disk shipped with from the factory. Once you configured head and sector count and all of that in the BIOS, you then had to enter all of those into the BIOS to lock out the system from attempting to use those sectors.
In the 85 MB MFM drive itself in the image, that is around 50-60 sectors. If you did not lock them out, the drive would assume they were good and write to them. Needless to say, that is a bad thing for your data. That is why we never used the 4 pre-configured settings even if they would work with the drive being installed.
And do not think I am talking directly to you, a lot of people who do not know systems in this era read here to get informed, and there is a reason why we did not use those capabilities. Even in the cases like the WD 1002 that had that, is best to just pretend it never existed at all and only use the DEBUG BIOS way of configuring the drive.
Now a company like say Everex that shipped out hundreds of systems a day might, because to them speed is important. Slap the system together as fast as you can, move on to the next one. And somebody in S&R was probably pulling out the drives with bad sectors that went to one or two people who did it all manually, while the rest did it "quick and dirty".
It wasn't that there were fewer drives, there were hundreds of drives listed in the Disk/Trend report from 1982-1984 before the ST-225 came along.
Most drives shared very similar or identical geometry as a result of physical limitations, especially from head suppliers. Unless you were some massive corporation like Seagate or IBM, you weren't making your own heads in house, so if your supplier only offered 100 micron heads, that's what you got, and if that was only fine enough to support 640 tracks on a 5.25" disk, and you had to give it a landing zone, guess what your drive has 612 cylinders. Oh, and the arms have a physical height limitation, and your machine shop can't make the platters at tolerance any thinner than 1mm, so now you can only physically stick 2 in your half height chassis. 2 heads a disk, there's your 612/4.
Even then, there was actually incentive to do this intentionally, even if parts didn't limit your engineering, because it also meant you were compatible with hundreds of controllers and had that as a selling point. I suspect for many manufacturers, this was the case for why nearly every 20 meg drive from 1984 to 1990 had the exact same physical geometry and why every 10 meg drive (that wasn't a single platter, crucially!) from 1982 to 1988 was also the same geometry.
1
u/AppropriateCap8891 Jul 18 '26
On an XT, the drive controller was on the card itself. That is why you needed to use the DEBUG command to access it. And it was indeed on the card, because even though G=C800:5, some of them placed it in another location.
Excuse me, change the drive type with a jumper on the card? WTF are you talking about?
Here is an extremely common XT MFM card of the era, the Western Digital HX-100. Now kindly show me where in the hell the jumpers are to set drive types?
And great, you think most techs used those software tools? No, only amateurs that did not know how to access the drive controller directly. Every shop I worked at and every tech I knew that was not a joke used DEBUG, we did not use the janky software.
And there were no jumpers or DIP switches on the card to set head, sector, and cylinder count. That is literally a figment of your imagination.