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:

• Western Digital - WD37C65
• National Semiconductor - DP8473
• National Semiconductor - PC8477
• National Semiconductor - PC87306
• Acer - M5105-A4E

With the exception of the (1st) Western Digital ISA cards all can handle 128 bytes/sector (FM, MFM) without any problems, see test results below.

• Western Digital - WD1003V-MM2 or WD1006V-MM2
• Adaptec - AHA-1522A or AHA-1542B
• TMC - IFSP (supports four FDD)
• CompatiCard IV
• ISA FDC by Sergej Kiselev (my recommendation)
• GW2760

My recommendation is the ISA FDC by Sergej Kiselev, but you have to assemble (solder) it yourself. The CompatiCard IV is of course perfect, but you will only be able to buy one if you are very lucky (it is rare and usually very expensive). This leaves only the AHA-1542B for most users. But you can also switch to SCSI hard disks. Also good!

The AHA-1542B cards are currently (09/2023) sold on eBay for about 60 EUR. Not a bargain but much cheaper than the CC IV (300-400 EUR).

Western Digital - WD37C65

This IC is the minimum you must have.

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).

National Semiconductor - 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]

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).

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

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).

• README (testfdc.txt) by Dave Dunfield
• WD37C65C (Western Digital)
• DP8473C (National Semiconductor)
• PC87306 (National Semiconductor)
• PC8477B (National Semiconductor)
• AHA 1542B (Adaptec Installation Guide)
• WD1006-MM1_2 (Wester Digital Users Guide)

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