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View Full Version : do IDE to MFM adapters exist? can one be made?



Mike Chambers
September 9th, 2006, 11:39 PM
i was wondering... do any IDE to MFM controller adapters exist? if not, could it be made?

i would think there has to be SOME way to do it, since IDE technically is compatible with the original seagate ST-506 controller standard for MFM/RLL drives. i believe the only difference is the connector, but i could be mistaken.

modem7
September 10th, 2006, 12:22 AM
The MFM interface (ST506/412 interface) and ATA interfaces are very different animals. Take a look at the pinouts on the Internet. An adaptor/converter is possible but would require electronics.

Mike Chambers
September 10th, 2006, 12:38 AM
The MFM interface (ST506/412 interface) and ATA interfaces are very different animals. Take a look at the pinouts on the Internet. An adaptor/converter is possible but would require electronics.

yeah you're right i just looked at pinouts... totally different.

mbbrutman
September 10th, 2006, 06:29 AM
In an MFM setup the controller does a lot of the work. In an IDE setup the work of picking the data out of the analog signal is done on the drive.

However, the software interfaces are nearly exactly the same. At the BIOS level a machine like an AT can't tell the difference between the two. For example, I replaced a dead MFM drive in an AT with a simple new IDE controller and IDE drive, and the poor machine thought it had a new 30MB drive. (I had not changed the CMOS drive type.) The same software in the BIOS of the machine was driving the new controller, which did not have a BIOS of its own.

(In reality it was a bad deal .. that drive was well over 500MB. I wound up installing drive overlay software to get access to the rest of it, as the built in BIOS on the AT wasn't sufficient.)

DoctorPepper
September 10th, 2006, 09:44 AM
Makes me wonder if it wouldn't be cheaper and easier to do something using a CompactFlash card. Give it an interface accessible via MFM and plug it in.

Any thoughts on this?

mbbrutman
September 10th, 2006, 10:37 AM
Find an 8 bit IDE controller and get a Compact Flash IDE adapter for it. Theoretically, it's possible.

dongfeng
September 10th, 2006, 10:56 AM
Would a CF card work? It sounds like an interesting idea, but I am wondering about how an XT would handle it.

Jorg
September 10th, 2006, 11:04 AM
Maybe finding something with SCSI might even be easier.

mbbrutman
September 10th, 2006, 11:16 AM
CF to IDE adapters are readily available. An 8 bit IDE adapter for the XT is hard to come by.

8 bit SCSI adapters are not hard to come by, but they don't grow on trees either. I've pointed out in many other threads that this is a better solution than trying to find 8 bit IDE adapters, or continuing to run ancient hard drives on an ST506 card.

dongfeng
September 10th, 2006, 11:56 AM
I was under the impression that IDE drives came in XT/AT formats - therefore you could not use an XT type drive in an AT type machine. I also heard that some early IDE drives where switchable XT/AT. Any truth in that?

mbbrutman
September 10th, 2006, 12:01 PM
Nope. ;-)

The issue is does the particular drive support 8 or 16 bit transfers. Most IDE drives are designed for 16 bit data transfers, and will not work on an 8 bit IDE bus. And it's not switchable .. that's just the way the drive is built.

If you had a slightly more sophisticated controller card, it could do 16 bit transfers to the drive and 8 bit transfers to the machine. It would require some buffering. But I don't think such a controller card exists mass produced, and nobody here is probably up to designing it.

People graft IDE drives onto C64s and other machines. Do some Googling to see how they do it. IDE isn't magic .. it can be done.

Terry Yager
September 10th, 2006, 02:17 PM
I was under the impression that IDE drives came in XT/AT formats - therefore you could not use an XT type drive in an AT type machine. I also heard that some early IDE drives where switchable XT/AT. Any truth in that?

Yes, no, and yes. 8-bit=XT, 16-bit=AT. The XT version may be used (with 8-bit controller) in an AT, but not vice-versa. The AT-IDE requires a 16-bit controller. IIRC, the Seagate ST-157 is one of the switchable ones (too lazy to look it up right now, but I'm sure someone will correct me if my recollection is faulty).

Edit: Come to think, the ST-157 came in more than one model, 157A, 157X, 157A/X, etc, the A/X model being the one that is usable on either interface (I could be fulla crap, tho).

--T

IBMMuseum
September 10th, 2006, 03:45 PM
yeah you're right i just looked at pinouts... totally different.
As said, the notion of IDE was the "controller" on the drive itself (which shows up with how a master & slave device are set up on the IDE channel). The IDE adapter cards were typically just buffer chips from the ISA bus (in the common AT design) to the drive. And a number of them that added an FDC and/or I/O ports.

IBMMuseum
September 10th, 2006, 03:50 PM
In an MFM setup the controller does a lot of the work. In an IDE setup the work of picking the data out of the analog signal is done on the drive.

However, the software interfaces are nearly exactly the same. At the BIOS level a machine like an AT can't tell the difference between the two. For example, I replaced a dead MFM drive in an AT with a simple new IDE controller and IDE drive, and the poor machine thought it had a new 30MB drive. (I had not changed the CMOS drive type.) The same software in the BIOS of the machine was driving the new controller, which did not have a BIOS of its own.

(In reality it was a bad deal .. that drive was well over 500MB. I wound up installing drive overlay software to get access to the rest of it, as the built in BIOS on the AT wasn't sufficient.)

I keep a unique ISA IDE/FDC adapter around for trying odd <512Mb drives on AT-class systems without user parameter drive settings. You just set the system for drive type 1. The controller gets the drive parameter settings itself & does all the translating...

Chris2005
September 11th, 2006, 12:30 PM
drives intended for say the IBM PS/2 Model 25 (and 30) and the later Tandy 1000 series were "8 bit" and called "IDE". I don't know if this helps or is even relevant. The PS/2 drives made have been somewhat different animals altogether. In other words they may have "borrowed" the term (IDE), in that the more electronics were integrated on the drive itself, but not to say it's a true IDE drive. I believe, though can't swear to it, that some of the drives that got mounted on cards (perhaps only for the Tandy's as mentioned) were kind of sort of IDE drives, but intended for 8bitters. You can read about this stuph in earlier manuals "like" Scott Mueller's books (not sure if I did read it in his or some other dude's). Looked into this in '94-95. My remembrance is understandably sketchy.
CF and to a degree even SD cards (and whatever else) readily and seemingly easily interface to microcontroller type processors. This shouldn't rule out hooking one to an 8088 or whatever else. Right now I'm trying to get my darned CNC mill going, so my head ain't into that project right now. But if someone else doesn't get to it, I will *eventually*.
There must be others, but Nuts -n- Volts magazine had an article within the last 8 months give or take that described the contruction of an mpeg player. Caught my eye cuz it in fact utilized a CF card for storage. Also available from Sparetime Gizmos, but you're not likely to learn anything just by buying the kit.

JohnElliott
September 12th, 2006, 01:58 PM
This is largely cribbed from a post I made to comp.sys.ibm.pc.classic last month.

When we're talking about PCs with an 8-bit ISA bus, there are four possible ways to get something that can be described as "IDE":

There's XTA as opposed to ATA (as Terry Yager says, selectable with a jumper on some drives but hardwired on others) where the drive electronics mimic an 8-bit XT controller rather than the normal 16-bit AT controller. This would only be available on pretty old and small drives.
More modern "IDE" (ie, ATA) adaptors for 8-bit ISA would, I hope, talk to the drive in its normal 16-bit mode and convert to/from 8-bit transfers when talking to the PC.
There's an optional "8 bit transfers" mode on some ATA drives (and all CompactFlash cards), selected using the SET FEATURES command. It's quite possible that this is what at least some 8-bit micro CF adaptors use.
Other ATA adaptors for 8-bit micros use the ATA interface in 16-bit mode but only read/write the low 8 bits of every word, thus halving the drive capacity.

Sadly, since I don't have any 8-bit ISA ATA interfaces (or SCSI-to-CompactFlash bridges), my XTs are having to make do with hard drives for now. My ideal would be a half-height 8-bit ISA card with the CF socket mounted directly on it, something like a mini-hardcard, but I don't think anyone makes them :(