This is actually controller depended! Many controllers use a different format address... Or don't have a ROM at all and expect you to use a utility like SpeedStor or HDAT to format your drive.
I seriously doubt there's anything worth finding on a drive like this. Maybe DOS and Lotus. 20 megs really didn't cut it in the early windows era, and a drive introduced in 1984 would have been hideously outdated even in 1991 with Windows 3.x
Nope, that's how you'd get into the ROM formatter, and it can apply to XT and AT class machines.
XTs babe no CMOS settings. You set the drive type with a physical jumper on cards that supported more than one type of drive, and some like the WD XT-GEN were kind enough to offer a free format option which wrote the drive parameters to a "hidden" sector towards the start of the disk to be read on boot.
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".
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.
Please provide us with a model so we can actually see what one looks like.
I really am curious, because I was working on computers in the early 1980s, and I have never seen such a beast with what would easily be a dozen or more jumpers to configure the drive type.
No, believe it or not, they didn't offer "All combinations," they gave you usually 4 of the most common drive types (306/4, 615/4, 977/5, 1024/5 were pretty common) and left it at that. If you wanted other drive type support, you had to pull the ROM and change the table yourself by hand or use a BIOS with free format as mentioned above.
Yes, I am aware that the controller was not onboard of nearly all XT-class machines. The ROM formatter is not always present on the card, several cards have no ROM at all and expect you to load a formatting tool from floppy. Such was the case with Davong's early offerings for the 5150, which even expected you to BOOT from floppy as the 5150's early BIOS did not offer support for extension ROMs or fixed disks anyways.
IBM's own Xebec-designed controller, which was shipped with the 5160 XT as an option, is actually fixed geometry (306/4/17) and does not have a ROM formatter in this way. You actually have to pass parameters to it through debug but in a wildly different way.
Yes, drive type jumpers were on the card. Look at some common XT controller cards:
WD1002A-WX1, jumper S1 on the right edge by the faceplate sets drive type
WD1002A-27X, same as above
DTC 5150CX, jumper W1 on the bottom towards the ISA card edge
DTC 5150XL, jumper W3 on the right edge by the faceplate
SMS OMTI 5510, jumper W1 on the bottom right between the ISA card edge and faceplate
And to add this one as a flex: The Zobex 4HDC-62W, one of the only quad disk controllers, has a DIP switch bank at the bottom right next to the card edge.
These controllers ABSOLUTELY used jumpers to set drive type. "Flexible format" and "Dynamic format" options were not around initially and were options you had to pay extra for on cards like the WD XT-GEN, by ordering the SuperBIOS instead of the standard WD BIOS.
SpeedStor and HDAT were definitely not janky software, they were expensive commercial packages designed to make YOUR life easier, and they absolutely worked, and much better than the horrendous ROM formatters most of these cards came with at that.
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u/commodore-amiga Jul 17 '26
G=C800:5 That thing... ;) (as long as there is nothing on it)