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Single & Double Density – FM & MFM

Last revision of this chapter: February 8, 2025

Image created with AI in Bing Image Creator by retrocmp.de
Image created with AI in Bing Image Creator by retrocmp.de

I use the program TESTFDC by Dave Dunfield to evaluate the capabilities of a 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. [3]

Dave Dunfield has conducted a number of tests on mainboards and floppy controllers. For this reason I want to limit myself to few good floppy disk controller chips. These are:

With the exception of the first, all can handle 128 bytes/sector (FM, MFM) without any problems.

  1. Western Digital – WD1003V-MM2 or WD1006V-MM2
  2. Adaptec - AHA-1522A or AHA-1542B
  3. TMC - IFSP (supports four FDD)
  4. CompatiCard IV
  5. ISA FDC by Sergej Kiselev
  6. DTK PAM-0055I-E0 (a very good mainboard)
  7. GW2760

Western Digital – WD37C65

This FDC is the minimum you must have.

LCS-6623 REV N1: IDE/HDC and FDC (WD37C65)

The LCS-6623 REV N1 does not support 3.5" ED floppy drives with 2.88 MB, because there was only a 9.6 MHz (for 300 Kb/s) and a 16.0 MHz (up to 500 Kb/s) oscillator on board! You need a 32 MHz oscillator for 1 Mb/s.

The main difference between the WD37C65 B and C is, that model C supports data rates up to 1 Mb/s (MFM) while model B supports only up to 500 Kb/s (MFM).

WD37C65/A/B/C
Differences between the various WD37C65 FDCs

National Semiconductor – DP8473V

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

National Semiconductor – PC8477

This IC is the enhanced version of the former DP8473V.

CompatiCard IV and ISA FDC by Sergej Kiselev.

National Semiconductor – PC87306

Besides the DP8473 and PV8477 floppy disk controller ICs there is also the PC87306 by National Semidonductor. This is a Super I/O & FDC controller used on mainboards like the DTK PAM-0055I-E0 or the P51430VX/250DM EXPLORER II.

The FDC [PC87306] is fully compatible with the PC8477 and incorporates a superset of DP8473, NEC mPD765 and N82077 floppy disk controller function. [2]
Super I/O PC87306 [1]
DTK PAM-0055I-E0 with PC87306 [1]

The DTK PAM motherboard does not appear in Dave Dunfield's well-known list! With this board you can build a perfect floppy test and disk imaging station; simply ingenious.

P51430VX/250DM EXPLORER II with PC87306 [1]

Acer – M5105

This Super I/O card with the Acer M5105 FDC is also perfect. You have a very good floppy and hard disk controller and all necessary interfaces (COM1, COM2, LPT1, GAME).

Acer M5105-A4E
GW2760-V4: Super I/O, IDE/HDC, FDC (Acer M5105)

Many of these cards are currently (09/2023) sold on eBay for about 50 EUR. Not a bargain but better than the CC IV.

Test Results

  1. WD1006V-MM2 - WD37C65BJM - 360K
  2. WD1006V-MM2 - WD37C65BJM - 1,2M
  3. LCS-6623 N1 - WD37C65CJM . 250 ..... 360K
  4. AHA-1542B - DP8473V - 360K
  5. AHA-1542B - DP8473V - 360K *)
  6. AHA-1542B - DP8473V - 1,2M
  7. CompatiCard IV - PC8477AV - 360K *)
  8. CompatiCard IV - PC8477AV - 1,2M *)
  9. GW2670 - Acer M5105 - 360K *)
  10. GW2760 - Acer M5105 - 1,2M *)

Basically all above FDCs are good. All can read and write single density (FM)! But the CompatiCard IV, AHA-1542 and GW2760 are better because they can also handle 128 byte sectors in FM and MFM.

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

Manuals

Reference

  1. (↑) eBay sales pictures
  2. (↑) PC87306 Super I/O data sheet
  3. (↑) Dave Dunfield, testfdc.txt