Oops, now that my memory is returning, the RK02 was the same geometry but half-density. RK02 carts say "1100BPI", RK05 carts say "2200BPI". Was there a RK04? == page 1-1 of the RK11-C manual (RK11-C_manual1971.pdf) "The high-density option provides a choice of either the RK03 Diablo Disk Drive Unit or the RK05 DECpack Unit, both utilizing the RK03-KA, IBM Type 2315 12 sector high-density disk cartridge. The low-density option provides a choice of either the RK02 Diablo Disk Drive Unit or the RK04 DECKpack Unit, both utilizing the RK02-KA IBM Type 2315 12-sector low density disk cartridge". low density is 12 256 byte sectors (1100 bpi) high density is 12 512 byte sectors (2200 bpi) both are 203 cyls, 2 tracks. I can't imagine there were many RK04's made..