12" Floppy Disks

Johnny Billquist bqt at update.uu.se
Tue Sep 15 13:19:34 CDT 2015

On 2015-09-15 19:03, Paul Koning wrote:
>> On Sep 15, 2015, at 12:28 PM, tony duell <ard at p850ug1.demon.co.uk> wrote:
>> ...
>> AFAIK the RK04 never existed. The RK02 and RK03 were re-badged Diablo Model 30
>> drives, the 02 being low density and the 03 high density. The RK05, very well known
>> was a DEC drive of the same capacity, physical track format, etc as the RK03 (that is
>> 'high density, about 2.5 MBytes on a disk).
> There was also an RK08, as I recall -- same platter as the RK11/RK05 but 16 sectors per track instead of 12.
> If I remember correctly, that same 16-sector platter was used in the IBM 360 model 44 which had an RK05 lookalike built into the CPU cabinet (on the side).  I never used it; not sure if OS/360 supported it, that might have been PS/44 only.  If yes, one wonders if it was fixed size sectors, a rather un-OS-like thing to do...

Actually, the disk pack don't change the designation here.
The RK05 was used both on PDP-8 and PDP-11 systems. On a PDP-8 you use a 
disk with 16 sectors, while on the PDP-11 you use a disk with 12 
sectors. And, of course, on the PDP-8 you have 256 12-bit words per 
sector, while on the PDP-11 you have 256 16-bit words.
So it ends up being the same number of data bits per track.

So the disk packs themselves had different designations. But the drive 
is identical.

As far as I know, there never was a RK08. The RK06 and RK07 were the 
last two with that designation.


More information about the cctalk mailing list