hard disk compatibility

HDD interface.

VAPCMD

I don't know of any hard disk that was designed for Windows 98. Are you wanting to put a hard disk with Win 98 installed on the same PC as one with Win 7? Well, Win 7 would be able to see and read from it but you'd probably not be able to run Win 98 on the same machine. The primary reason is that the amount of RAM needed to run Win 7 would choke Win 98. Are we close to answering you here?

All HDs will work provided there is no fault present. Further, understand small older HDs may not be desired not because of OS format but rather it needs juice from PSU by being present. Thus, I won't install an old HD that's smaller than 20gb in size to be practical, IMHO. If you want to use a smaller HD like say 10gb, etc. mount it in the proper ext. case and use it as ext. HD. Seriously consider that you think using a "flash drive" as these are very capable and come easily in 4-16gb capacity. Of course, you have to prepare any old HD for use and in most cases that FAT32 or NTSF. This is a generic answer and you didn't state what size old HD you're inquiring about.

tada -----Willy

First a hd is not designed for an OS.....it's just a storage device and could not give a hoot what OS or data you put on it.

The maybe part.

Hd's from the w98 era were PATA.

Hd's from the win7 era are SATA.

The cables and plugs are different.

So a quick eye-ball of the old hd connectors and the connectors available in the machine might be of value.