2018-2020.
Why care about being able to read legacy 5.25-inch floppy diskettes? Sometimes, one of them will contain an irreplaceable treasure. It might be the forgotten words of a poem or song you wrote. I wanted to be able to check before throwing anything away. But Intel removed motherboard support for 5-1/4 inch floppies in 1998 and 3-1/2 inch floppies in 2002, though PCs were still being sold with them after that.
I arranged to overrule Intel. From descendants of IBM OS/2, this is completely transparent (ArcaOS and EComStation 2020). I can simply address the 3-1/2 inch drive as 'A:' and the 5-1/4 inch drive as 'B:', despite Intel having dropped dual drive support! And with the assistance of Sydex 22disk, which you can still register, I find I can still read floppy disks created with the CP/M Kaypro 2 as long ago as 1983 (Sydex 2020). Here's how I did it:
Trap: You might not be able to plug your floppy cable onto the drive. Some cables plug hole 3 and expect the drive to have no pin 3 so a backward connection is not possible. Workarounds: get a cable without the plug or cut pin 3 off the drive. It's moderately safe to cut pin 3 off. It's just an extra ground.
Trap: If your cable has the card edge connector, you might be tempted to just use an old 5-1/4 inch drive. This won't work with old 360-kilobyte drives unless you have an old motherboard that still supports their logic levels. Workaround: get an old 1200-kilobyte drive like the Newtronics model Mitsumi D509V5, which is compatible with 3-1/2 inch drive logic levels.
Trap: If your motherboard is old enough to support 360-kilobyte drives, really old ones like the Panasonic 5-1/4 inch 360 kilobyte JU-475-3 and -4 will show permanently not ready. Workaround: Tape over pin 34 and set the operating system flag for no change line support, e.g., in DOS \config.sys, 'drivparm=/d:0 /f1'.
Trap. Unlike OS/2, MS-DOS cannot select drive B without dual drive support in the BIOS. Workarounds: You can switch strapping, or connectors, to choose the drive you need to work with. Alternatively, you might be able to install a drive select switch, but that's fraught with difficulty (Paarman 1986).
The strapping options are:
| End connector: | O/S Drive A selects 5.25in. |
| Mid connector: | O/S Drive A selects 3.5in. |
| Left column (2) | Strap pins A to B; and D to E. |
| Right column (1) | Strap pins B to C; and E to F. |
| End connector: | O/S Drive A selects 3.5in. |
| Mid connector: | O/S Drive A selects 5.25in. |
| Left column (2) | Strap pins B to C; and E to F. |
| Right column (1) | Strap pins A to B; and D to E. |
From OS/2, drive A now accesses 3-1/2 inch 720- and 1440-kilobyte disks, while drive B accesses 5-1/4 inch 360- and 1200-kilobyte disks.
Trap: If you write to 5-1/4 inch disks holding data written on 360-kilobyte drives the disk may be damaged beyond recovery. I've seen this result in readback with intermixed contents of old and new data. The problem is that the 1200-kilobyte drive only overwrites a narrow strip of any track previously written by a 360-kilobyte drive. Workaround: Protect 5-1/4 inch disks holding data written on 360-kilobyte drives by putting black electrical tape over the write-protect notch. Don't reuse them without bulk tape erasing them before reformatting them. The RoBINS Magnetic Bulk Tape Eraser TM-88 (R24-015-922) currently runs around $30 used.
To format disks for MS-DOS:
- format a: [/f:1.44)
- Format a 3-1/2 inch high-density disk (1.44 megabytes). The /f:1.44 is not required.
- format a: /f:720
- Format a 3-1/2 inch double-density disk (720 kilobytes). The /f:720 is required.
- format b: [/f:1.2]
- Format a 5-1/4 inch high-density disk (1.2 megabytes). The disk must be a high-density disk. The /f:1.2 is not required.
- format b: /4
- Format a 5-1/4 inch double-density disk (360 kilobytes) in the 1.2-megabyte drive. Per the warning above, if the disk holds data written by a 360-kilobyte drive, bulk tape erase it first. The /4 is required.
To work with disks in CP/M formats, I obtained the Sydex shareware 22Disk. I installed it in OS/2-DOS. With the OS/2-DOS settings HW_ROM_TO_RAM=ON, HW_TIMER=ON, and IDLE_SENSITITY=100, it even works in a window.
Trap. You can't read single-density disks such as the Xerox 810 single-sided single-density format often used to distribute bundled CP/M Kaypro II software. Reportedly, after the PC switched from the then conventional CP/M WD FD1793 controller to the NEC µPD765 controller, you could still read single-density disks by covering the index hole with black tape. But the AT switched to the Intel 8272A chip and the PS/2 to the Intel 82072A chip so single-density support vanished. Workarounds: use a CP/M machine to copy the disks to a double-density format or use a conversion service.
In May 2018, having confirmed that 22disk works and works well, I emailed info [at] sydex.com to inquire about registration. They sent instructions for making a $25 payment via email using Paypal. After payment, they promptly sent me a download link with the latest full registered version.