12" Floppy Disks

tony duell ard at p850ug1.demon.co.uk
Tue Sep 15 11:28:32 CDT 2015

> > I wonder if he's thinking of the 14" hard disk cartridges, perhaps the
> > front loading
> > ones used in things like the RK05 drive.
> I have the platters from one of these drives. One of the "youngsters"

A fair number of list members have such drives, still operational. If I crane
my neck in just the right way I can see about a dozen of them of various types
waiting for me to set up my 'Large Machine Room'.

> brought
> in platters from a 5 1/4" drive to show off his IT cred. Then one of the
> older
> youngsters brought in  a ~9" platter from some SMD drive. I brought in the
> ~14" platter from a very old DEC drive that crashed (RK04  sticks in my
> head, but I might be wrong).

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). The RK04, had it existed, would have been
the low density version of the DEC drive, but I can find no reference to it anywhere.

The RK02 to RK05 took a front-loading disk cartridge containing a single 14" disk. It was
intended to be interchanged by the user, like a floppy disk [1]. There were many other
models of 14" drives, some were designed for the user to interchange the disks (some 
front loading, some top loading) others were more like a modern hard disk and were
sealed winchester-type units.

[1] For the pedants, I do know what an RK05F is....

On drives where the user was expected to interchange the disks, a headcrash was not 
uncommon (due to contamination from dust when the drive is open, especially if 
the absolute air filter wasn't changed regularly). This was nearly always fatal to the disk,
often it wrecked the heads too (but not always, there are plenty of stories of RK05s 
(particularly) where there was a headcrash but the heads cleaned up fine) but it was
not normal to replace the drive when this happened. Not being a sealed unit, you could
replace the heads and other parts in the field, you did not need a cleanroom. 


Perhaps this is what he's thinking about?


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