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Load 5-1/4 Inch Floppy Disk Files on Aging Intel PCs

May 2018. How do you get data off of an old five and a quarter (5-1/4) inch floppy disk? With malice aforethought, Intel elected to shred our history by removing support for 5-1/4 inch archive disks in 1998. But support for a single three and a half (3-1/2) inch floppy drive continued for some time. A little known fact is that such a system can be pressed into service to read 5-1/4 inch floppies by reconfiguring it to actually work correctly with a high density 5-1/4 inch drive.

You'll have to find a PC old enough to have come with a 3-1/2 inch floppy disk drive. It's possible to maintain support for both a 3-1/2 and 5-1/2 inch drive. But it's not convenient. Switching between them generally means modifying the \config.sys file, turning off the PC, opening the case, physically swapping ribbon cable connectors or changing drive jumpers, and rebooting. But it does work. Here I assume said PC boots Windows 98, 95, MS-DOS, or OS/2 EComStation.

  1. You'll have to obtain a high density 1.2 megabyte 5-1/4 inch drive that uses the ribbon cable connector or if card edge is known to use 3-1/2 inch logic levels. Post 1998 Intel PCs do not support drives that use classic 5-1/4 inch drive logic levels. Here are examples of compatible and incompatible drives:

    You should be able to get a compatible drive on an auction site for around US $30. It's unwise to pay more, since there can be no assurance that it is compatible or working until you try it. Beware of buying on a mass market site, where even today the demand could drive the price north of $300.

  2. Even with a compatible drive you might have to cut pin 3 off of the connector in order to plug the floppy cable into it. This is because the final iteration of the floppy cable includes a plug in pin 3 to prevent connecting it backwards. (It's safe to cut the pin off. Pin 3 is just an extra ground connection.)
  3. You have to use a connector and drive jumper setting that taken together make the PC's drive A reach the 5.25 inch drive. The standard was that all drives were configured as physical drive B. The floppy ribbon cable had an untwisted middle connector and a twisted end connector. This connected the PCs logical drive A to the end drive and its logical drive B to the middle drive.
  4. To make both drives available without physically opening the PC, you'll have to install an external switch. See Paarman, Drive Select Reversing Switch, Micro Cornucopia, April-May 1986, at 47, available as a 108 page 11.6 megabyte PDF via archive.org/details/bitsaver_microCornua29Apr86_12184196.
  5. You also have to set the PC to be aware of the current 'drive A' geometry. It's unlikely that the BIOS CMOS setup menu will still have an option to select 5-1/4 inch 1.2 megabyte geometry. You'll probably have to use operating system configuration instead:
  6. You should write protect disks that were formatted or written to in 360 kilobyte drives. You can do this by placing a bit of black electrical tape over the notch in the disk. If you allow your high density 1200 kilobyte drive to write to such a disk, you may damage it beyond recovery. A symptom is that the very same file may have different contents depending on the precise alignment that the heads happened to be in at read time. It may even have intermixed contents. I've seen this. For the same reason, using 'format a:/4' to sanitize an old 360 kilobyte disk is not adequate. You have to bulk tape erase it instead. The RoBINS Magnetic Bulk Tape Eraser TM-88 [R24-015-922] for reel-to-reel tapes would do nicely -- they usually run under $30 used. After that, format a:/4 might be used if it was essential to prepare it for transporting data to an old PC, but there are no guarantees.
  7. You can only read foreign disks, such as CP/M disks, if they're double density disks, and only with the assistance of software such as 22disk. Modern PC controllers don't support single density disks. I have a handful of Kaypro software distribution diskettes evidently in an obscure Xerox 820 signal density format. But by far the majority are double density. And they're easily readable with the old shareware 22disk. It reads my Kaypro II'83 single sided and 2'84 double sided disks just fine. It even works in an OS/2 DOS window, provided the DOS box settings include HW_ROM_TO_RAM=ON and HW_TIMER=ON, though full screen is arguably safer.
  8. It's reportedly no longer possible to register 22disk, so using it for production work is of dubious legality. Reportedly, the original company Sydex sold rights to another company, and they to a third. Reportedly, Syndex indicated that continued distribution of the shareware wasn't prohibitted. That doesn't make sense if they don't still offer registration. I have sent an inquiry to Sydex, which is still in buiness in 2018.

Why would you possibly want to go through this trouble to use ancient, long-obsolete, deprecated, dated, 5-1/4 inch floppy disks? Because they're there, of course. And because corporate America shouldn't be allowed to erase our history.

Here ends the lesson in obsolete knowledge for today.


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