Replacing Vintage Hard Drives

In Vintage Computing \ Tech Tips

Working with vintage PC’s often involves retrofitting new parts. A common example is replacing aged failing hard drives. The BIOS in many 286, 386, and some 486 machines were hard-coded to support specific makes and models of hard drives and wouldn’t work with anything else. Some machines, of that era were more flexible in this regard but it’s a common issue nonetheless.

One common practice is use flash memory devices such as Compact Flash and SD Cards to replace IDE hard drives. Most CF Cards have native ATA mode support and are almost a direct interface with the adapter handling mostly just physical connectivity. SD-Cards on the other hand aren’t ATA compatible so their ‘IDE Adapters’ include a microprocessor that handles the translation. I’ve had good luck with both and to my surprise often find better performance with the SD-Card adapters than Compact Flash.

Here are some common tactics to retrofit a non-original drive into a Vintage PC.

  1. Check to see if your BIOS supports custom drive types. If it did then you probably wouldn’t be here reading this right now.
  2. Use a SCSI drive and controller. Bootable SCSI hard drive controllers have their own onboard option ROM that the PC’s BIOS will detect and enable circumventing any dependencies on the system BIOS. The drawback to SCSI is that it’s more complex, more expensive, and requires that the computer have expansion slots. Most laptops don’t have expansion slots making SCSI a non-option (with some exceptions such as the Toshiba T3200sx, T5200, and others).
  3. Options ROMs such as XT-IDE. Since the system BIOS looks for and executes option ROMs they can be used to override stock BIOS functions. XT-IDE is an option ROM that performs auto-detection and accessing IDE drives. The general concept is to disable the hard drive within your system BIOS and let XT-IDE handle things instead. The trick is getting XT-IDE into your system. You must either embed it into empty space in the system BIOS and make code changes to tell the BIOS where to find it or put it on a separate EPROM and interface it to the PC via an add on card. There are special cards for this purpose or a network card with a ROM socket can be used.
  4. Use an IDE controller that has it’s own BIOS onboard. This is the same concept as SCSI except it’s an IDE controller with an option ROM. These controllers can be rare, costly, and the same limitations are present (the computer must have an expansion slot).
  5. Modify your BIOS to add native support for your new drive. This is not for the faint of heart but usually provides good performance and the cleanest result (no observable difference from a stock machine). It involves reverse engineering your computer’s BIOS, knowledge of Assembly Language, patience, and usually the ability to program EPROM chips.