Hardware / CompactFlash // retrocmp / retro computing

It Can't be Quieter Any More!

The following points should be considered when using CompactFlash (CF) cards as a hard disk replacement.

DOS Partition Limitations

You can buy CF cards in all sizes for very little money, from megabyte to gigabyte, but ... most are completely oversized for use in DOS retro computers! Depending on which version of DOS you use, there are strict limits:

DOS 1.__: no HDD
DOS 2.__: 16 MByte
DOS 3.30: 32 MByte
DOS 4.__: 2 GByte
DOS 5.__: 2 GByte
DOS 6.__: 2 GByte

As of DOS 3.30, however, it is possible to create several partitions with FDISK. On an 8GB CF card, you can thus create four individual partitions of 2GB each under DOS 6.22.

Setting up the BIOS Parameters - CHS

If you want to use a CF card in an IDE adapter, you still have to enter the correct data for the "hard disk" in the PC BIOS. Almost all better BIOS use the so-called type 47 for this purpose. In this case, you can enter the values for cylinders, heads and sectors manually.

But even when everything seems to be in order, it doesn't work anyway. On my IBM XT/286 with AMI BIOS, for example, it is not possible to successfully configure a card larger than 48 MB! When booting, I always get the message: HDD controller ERROR. I do not know why. Sometimes the only thing that helps is trial and error.

Below are a few parameters for CF cards that I have gathered over time.


  mb   cyl  hds  sec        bytes  note
--------------------------------------- 
  16    30   16   63   15,482,880 
  32    60   16   63   30,965,760
  48    90   16   63   46,448,640   (1)
  64   120   16   63   61,931,520
 128   246   16   63  126,959,616
 256   493   16   63  254,435,328
 512   987   16   63  509,386,752   (2)
---------------------------------------
(always with 512 byte/sec)

(1) I use a DELOCK converter
    IDE 40/44 pin to CF with a
    SanDisk 48MB consumer card
    with my IBM XT/286 and AMI BIOS.
(2) the limit is 1,024 cyl.

As a rule, however, the CHS limit is always 1024/16/63, i.e. 528MB, at least on the older 286 or 386 systems.

According to Mueller, Scott (2003): Upgrading and Repairing PCs there are the following CHS limits (page 661):

Combined CHS BIOS and ATA Parameter Limits

For more detailed information, please read the chapter "Drive Capacity Limitations" from page 658 onwards.

Bootable or Not / Fixed or Removable?

I still have some old CF cards from about 1999. Although these are consumer cards, they are still bootable, but ... Since the middle of the 2000s the big companies have put a stop to this and developed so-called „Industrial Grade“ cards. These were also much more expensive at that time! Not any more today.

Consumer CF cards can only be used as a removable disk, whereas Industrial CF cards are used as a fixed disk.
Original citation Transend.

So don't be surprised if one or the other CF card is not bootable. All cards can be formatted and described, you will only notice the difference at booting.

My CompactFlash Cards — Some "bootable" CompactFlash Cards

My favourite DOS 3.30 CF card is the "SanDisk Industrial Grade" with 32 MB.

How to prepare the CF card

The easiest way is to create a bootable CF card with MS-DOS 6.22.

Create a suitable partition with FDISK and make it ACTIVE
Initialize with FORMAT /S
FDISK /MBR

Step 3 is very important. Every "bootable" CF card should now be bootable, if not try another card. If you don't use MS-DOS 6.22, see also the link to WipeDisk!

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