The Hard Drives: "HD10", D9060, D9090
As history tells it, Commodore's attempts to end their 8-bit line were all unsuccessful and the 64 continued to be manufactured almost up to the time of Commodore's demise as a corporate entity in 1994. If Commodore had managed to make the "HD10" or a derivative cheaply enough, the 64's lifespan might have been even further extended.
The 9060 was an IEEE-488 hard drive with 5MB storage and Commodore DOS 3.0 (might be the same version in the 8280). Since keeping a BAM on a 5MB+ unit would be unwieldy in RAM (geez!), a different mechanism of maintaining allocation tables is employed, but the user commands are the standard Commodore set. (A 9090 can take up to two hours to format the drive when issued a NEW command!) The 9090 is identical to the 9060, but has 7.5MB, and may be the hard drive used in the 700 series.
According to Ethan Dicks, the only discernable difference between the two is a jumper and the drive mech: the 9060 has the TM602S, while the 9090 has the TM603S. The drives are powered by a 6502 processor, with 4KB RAM internally, and a couple of 6532 RIOTs for I/O manipulation. The board is very similar to the PET 4040 disk drive, except for an additional SASI-ST506 board, instead of the D/A board in the 4040. Ethan also provided these statistics on the units:
TM602S: 4 heads, 32 sectors per track, 153 cylinders - 19,442 blocks free
TM603S: 6 heads, 32 sectors per track, 153 cylinders - 29,162 blocks free
Track-to-track seek: 3ms; average seek: 153ms
Maximum sequential file size: 7.50MB (9090)/5.00MB; maximum relative file size: 7.35MB (9090)/4.90MB
According to Markus Mehring, despite their relative rarity and lack of support from Commodore, even as late as 1988 many German contractors continued to offer upgrades and repairs for the devices. 9060s could be bought from anywhere between 2x5MB to 2x16MB capacity (even "short formatting" such a device took about five hours (!)). Prices went as high as 1500DM.
The 9060/90 units have a rich set of diagnostic error codes, like the 8250 disk drive:
1 flash 6532, 7F, 7G 2 flashes 2364, 7D 3 2364, 7C 4 6502, 2114, 74LS157, 74LS42, 4A, 5A, 5E, 6C, 6D, 6B, 6A, 3D 5 6810, 4D 6 2114, 74LS157, 5E, 5A, 6C, 6D, 6B, 6A 7 2114, 74LS157, 5B, 5F, 6C, 6D, 6B, 6A 8 2114, 74LS157, 5C, 5G, 6C, 6D, 6B, 6A 9 2114, 74LS157, 5D, 5H, 6C, 6D, 6B, 6A 10 2332, 4C 11* Not used 12* 74LS157, 6C, 6D, 6B, 6A 13 74LS157, 6C, 6D, 6B, 6A 14 74LS157, 6C, 6D, 6B, 6A* During format, 11 or 12 flashes indicate an excessive number of bad sectors.