Floppy Disk Controller / Capabilities

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Keywords: FM, MFM, SD, DD, 128

I use the program TESTFDC by Dave Dunfield to evaluate the capabilities of the floppy disk controller chip.

"This program evaluates the floppy disk controller in your system to determine how well it performs at single/double density at various data rates. It also tests MFM operation with 128 byte sectors. Many PCs cannot access these disk types. If you plan to use my ImageDisk program to archive and restore non-PC format disks, this program should help you find a PC thats up to the task."
Dave Dunfield (README: testfdc.txt)

Dave Dunfield has conducted a number of tests on mainboards and floppy controllers. For this reason I want to limit myself to two very good floppy disk controller chips. One is the WD37C65B from Western Digital and the other is the DP8473V from National Semiconductor.

The two ISA floppy disk controllers are the Western Digital WD1003V-MM2 or WD1006V-MM2 and the AHA-1522A or AHA-1542B from Adaptec. Especially the Adaptec controllers are perfect, they can handle 128 bytes/sector and single density (SD) without any problems. See my test results for the AHA-1542B below!

So far I have always used the WD1003V/1006V-MM2 floppy controllers. But I switched to the Adaptec SCSI controller AHA-1542B now. The SCSI function don't have to bother you. You can switch off the SCSI function and the BIOS with jumper J6-1, see installation guide. But even with the BIOS switched on, the card works perfectly.

I still use an MFM controller for my two hard drives (usually Seagate ST225). As hard disk controller I use the WD1003V/1006V as variant MM1, i.e. without FDC.

My Copy II PC OptionBoard Deluxe is also inserted between the floppy disk controller and the floppy disk drive. Everything works fine.

Update: 28.05.2019

I have exchanged the Adaptec card for the CompatiCard IV in my 386DX test computer. Basically everything was ok, but when accessing (single density) my Mitsubishi M2896 (8 inch, best ever!) with UniForm-PC 2.05 it didn't work properly. The reason is UniForm-PC 2.05, not the DP8473V FDC. You need UniForm-PC 3.0. With UniForm-PC 3.0 Beta you can directly select the CompatiCard IV. UniForm-PC 2.05 is still a very old version and actually meant for the CompatiCard I. The CompatiCard IV has the so called SuperFDC PV8477AV from National Semiconductor.

AHA-1542B
Adaptec: SCSI and floppy disk controller (AHA-1542B)
DP8473V
Adaptec: Floppy disk controller chip (DP8473V)

Wolfgang Kainz-Huber from Computermuseum M√ľnchen also recommends an Adaptec SCSI controller card with floppy function. However, he uses an AHA-1542C. I also have such a card, but mine has a Zilog Z84C00010VEC FDC chip. It can't even read/write SD! The AHA-1542B is top of the range.

Besides the floppy disk controller chips WD37C65, DP8473V and PV8477AV there is also the PC87306 (National Semidonductor), which according to Dave Dunfield can also read and write the single density and the 128 byte format. But at the moment I don't have a corresponding FDC to confirm this. I don't know of any ISA controller card that uses this chip!

Test results

  1. WD1006V-MM2 .... WD37C65B . TEAC FD-55BR .. (360 KByte)
  2. WD1006V-MM2 .... WD37C65B . TEAC FD-55GFR . (1,2 MByte)
  3. AHA-1542B ...... DP8473V .. TEAC FD-55BR .. (360 KByte)
  4. AHA-1542B ...... DP8473V .. TEAC FD-55BR .. (360 KByte) *)
  5. AHA-1542B ...... DP8473V .. TEAC FD-55GFR . (1,2 MByte)
  6. CompatiCard IV . PC8477AV . TEAC FD-55BR .. (360 KByte) *)
  7. CompatiCard IV . PC8477AV . TEAC FD-55GFR . (1,2 MByte) *)

Basically all three floppy disk controllers are excellent. All can read and write single density (FM)! The CompatiCard IV and UniForm-PC 3.0b form a perfect team. They can read and write any format (CP/M and DOS)!

*) With Copy II PC OptionBoard Deluxe (FDC -> OB -> FDD).

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