Epson drives (Was: C64-C128 CP-M Cartridge Interest

[Tony Duell]

> I find it more interesting that some of the 135 tpi users selected 
> odd values for the upper limit.  HP used 66, I think and Jonos used 

the original HP 3.5" drive unit -- the 9121 was designed ot be exactly 
compatible with the 82901 5.25" drive unit. The latter was a 35 cylinder 
2 head deevce, so 70 physcial tracks. The 3.5" drive therefore only used 
70 physicla tracks too. But HP also had this idea f having 'spare' tracks 
so that slightly defective disks would appear perfect to the user. And 
this was handled by the drive unit. There's soem kind of infromation 
stored o nthe inntermost track whih gives the track replacemtn 
indromation, disk usage count, etc. No hP maual that I've seen has any 
real details of this.

The single-0sided drives in the earlier 9133 uniuts are the same as te 
9121 (to the exptent that the firmware EPROM on the controler board is the 
same)..The double-sided ones are different, I think you get something 
like 77 user cylinders on thsoe (and still some bad track informaiton on 
cylidner 79.).

-tony