PCs of a sufficient vintage had so little logic on the HDD that you could swap out the MFM controller card in your PC for an RLL one and get 50% more storage. The modulation of the signal written to the disk was the job of the controller card, not the board on the HDD. Turn your 20MB HDD into a 30MB with a controller change and reformat? Mighty tempting.
This 4GB Western Digital AC-14300 with mfr date of 1995 seems to have 512KB of cache? Not sure if these specs are reliable though.
- https://stason.org/TULARC/pc/hard-drives-hdd/western-digital...
- https://www.ebay.com/itm/325794470911?hash=item4bdadd1bff:g:...
This 250MB Samsung from 1993 has 64KB of cache:
- https://www.directitsource.com/product-p/shd-3122a-ds2.htm
- https://www.youtube.com/watch?v=d-X2uYEx7tU
This WD Caviar 280MB from 1992 seems to have 8KB of cache.
- https://www.ebay.com/itm/154446527853
- https://www.priceblaze.com/WDAC280-WesternDigital-Hard-Drive
This 40MB Maxtor from 1990 has 32KB of cache.
- https://stason.org/TULARC/pc/hard-drives-hdd/maxtor/8051A-41...
So, I think any contemporary hard drive in those days would have some cache. Thanks for leading me down this nostalgic rabbit hole.