12" Floppy Disks

Paul Koning paulkoning at comcast.net
Tue Sep 15 13:25:38 CDT 2015

> On Sep 15, 2015, at 2:19 PM, Johnny Billquist <bqt at Update.UU.SE> wrote:
> 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.

Yes, my mistake.  I was thinking of the RK05 class drive as used on a PDP-11, which apparently is "an RK05 drive and RK8 controller".


More information about the cctalk mailing list