I have an AST Premium Exec 386SX/20 Model 63V laptop minus a floppy drive and hard disk. Otherwise the 1991 vintage machine is fully functional (and in excellent condition, so it's definitely worth saving).

I've been using a modern SD-Card to IDE adapter (chip: FC1307A) to attempt to boot from a 128 MB SD-Card, and before the floppy drive died, I managed to get Windows 3.1 almost installed (it got to 99% and errored-out).

I am having a very hard time constructing a bootable image that will allow this laptop to run from the SD-Card. Part of the problem is that I have not been able to find any official settings for the hard disk geometry that this laptop expects to see on the IDE hard drive.

The original hard drive (now physically damaged and unusable) is a Conner Peripherals CP-2064. Sticker on the disk says it's a 60 MB and "TYPE=AUTO" whatever that means. The quality control stamps on the hard disk suggest a firmware version of "NT1.14".

How can I configure this laptop to recognise the SD-Card and boot from it? I realise this is not an easy question and will possibly require the assistance of someone who owns a working laptop of this kind...

  1. What is the correct BIOS configuration pertaining to the hard disk?
  2. How can I construct an SD-Card ISO image compatible with (1) that allows the volume to be bootable?
  • 1
    TYPE=AUTO means you can choose the AUTO configuration in the BIOS and it will discover harddisk geometry. So that doesn't help. What SD-Card to IDE adapter do you have, and does it support explicit geometries? And the first think I'd try is to get another SD-card, put it into another computer, install some variant of MS-DOS on it, and try to get that to boot.
    – dirkt
    Feb 5, 2023 at 16:28
  • @dirkt, the chip used on the adapter is a "FC1307A".
    – Wossname
    Feb 5, 2023 at 17:39
  • @dirkt, I did go through the process of attempting to write valid MS-DOS images onto the SD-Card (having made a virtualbox VM for this purpose and dding the data across). Couldn't get it to work. But I could not see why or where it was failing either - there were no descriptive error messages during the booting process. The system simply fails to boot without explanation ("missing system disk" or similar cryptic nonsense).
    – Wossname
    Feb 5, 2023 at 17:49

2 Answers 2


I have not been able to find any official settings for the hard disk geometry that this laptop expects to see on the IDE hard drive.

A few days ago I acquired a Toshiba T1800 386SX laptop with the same hard drive as yours (including same firmware version). Unfortunately the hard drive and floppy drive in my machine were also both faulty. I was going to trash it, but then I saw your question so today I plugged the hard drive into an old Pentium desktop PC using a 2.5 to 3.5 inch IDE adapter. This machine reported the following drive specs:-

  • Cylinders: 823
  • Heads: 4
  • Sectors: 38

These numbers match the specs provided on this website.

I'm not sure if that will be any use to you though. I have an SD to IDE adapter similar to yours. I put a formatted 128MB SD card into it which is recognized by the desktop PC, but the T1800 didn't think there was a drive there.

Perhaps if you put the SD card/adapter in a PC which can have CHS manually set in the BIOS, you might be able to partition and format the card in a configuration your laptop recognizes.

There is one other thing you might want to try - repairing the Conner hard drive. My drive made a series of knocking noises when starting up. In the specs I saw that:-

At power down or the start of STANDBY MODE or SLEEP MODE the heads are automatically retracted to the inner diameter of the disk and are latched and parked on a landing zone that is off the data tracks.

I suspected the problem might be that the latch was stuck. So I whacked the side of the drive towards the IDE connector end (where the latch likely would be) several times with a large screwdriver. The drive now works!

Turns out this is a common problem with Conner hard drives. The latch mechanism (shown here) consists of an arm attached to the voice coil that 'sticks' to a small stationary magnet when the heads are moved inwards to the parking zone. A rubber bumper provides a gap so it doesn't stick too strongly to the magnet and prevent the heads being moved off the parking zone. Over time the rubber may become sticky itself, especially if the drive has been parked for a long time.

Whacking the drive on the side 'unsticks' the latch and allows the heads to move again (at least until the next time the drive is left parked). Some people have opened up their drives and put a piece of tape over the bumper to stop it sticking. I don't recommend that because dust could get inside and cause a head crash. However if whacking it doesn't work then you have nothing to lose...

  • That's an amazing stroke of luck! I really appreciate you doing some investigative work on my behalf, thank you so much. You are right about the sticky head parking. I opened the lid on my HDD and indeed the head had adhered to the end-stop, and I managed to free it by poking it with a calibrated finger! Sadly though the HDD is still kaputt, and simply spins up loudly to some absurd RPM and draws a couple of amps of current. I'll abandon that and continue with the SD-Card. Again many thanks for your efforts :)
    – Wossname
    Feb 6, 2023 at 17:44

According to this, the FC1307A works in LBA mode, has not been tested in CHS mode, and the datasheet (which could answer those questions) is hard to find.

So I'd try to install Freedos, which works with LBA, on another SD card and see if you can get that to boot.

I can't remember if Windows 3.1 boots using LBA only, maybe somebody else nows. But it may not work if it doesn't, and the adapter doesn't support CHS.

The aggravating thing is that I can't see what's going on during the boot process.

Syslinux has diagnostic tools for the boot process.

Laptop gave a new message upon boot attempt: "read error while reading drive" (verbatim)

If the BIOS tries to read the boot sector with CHS, and the adapter only does LBA, then there is no way to get this to work with this adapter.

  • Tried FreeDOS just now. Laptop gave a new message upon boot attempt: "read error while reading drive" (verbatim) and then hangs. The aggravating thing is that I can't see what's going on during the boot process.
    – Wossname
    Feb 5, 2023 at 18:56
  • LBA only works if the ROM-BIOS has these extensions so it may do little good.
    – ecm
    Feb 5, 2023 at 19:17
  • 1
    LBA is used only between the BIOS and the drive. Anyone who accesses the drive via the legacy BIOS interface (i.e. DOS), it will use CHS. The BIOS is likely too old for understanding LBA, as it was added only somewhere in the 486 era, so some 486 computers will also be limited to seeing a 504MB CHS drive even if you had a larger drive. And you have to let the PC use the same geometry as the IDE to SD adapter shows you, or it can be used with smaller parameters in BIOS but then there are gaps so the SD card so no other PC underatands the mapping.
    – Justme
    Feb 6, 2023 at 6:25

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