I'm almost sure that he's thinking in one 5 1/4" of 1.2 mb capacity. Kind Regards Sergio Pedraja 2015-09-15 10:51 GMT+02:00 Eric Smith <spacewar at gmail.com>:

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'. 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. -tony Perhaps this is what he's thinking about? Warner

I thought the RK(0)8 was the controller for a PDP8 system. I have an RK8E in my PDP8/E, it links to a normal RK05 drive. It does indeed use 16 (hard) sector packs, unlike the 12 sector ones used in the same RK05 drives linked to an RK11 controller (RK11C, RK11D, RKV11D) on a PDP11. The HP7900 drive uses the same type of cartridge but 24 sector. -tony

On 2015-09-15 19:03, Paul Koning wrote: 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. Johnny

On 2015-09-15 20:25, Paul Koning wrote: Yeah. Except I bet you meant "RK05 with an RK11 controller" above. Or else "as used on a PDP-8". :-) I like RK05. It's very reliable. And plenty for a PDP-8... Heck, OS/8 have to treat it as two disks, since it is so huge. :-) Johnny

In this day and age, nothing surprises me. The question also hinges on the nationality and age of the questioner. A common 5.25" floppy is about 13 cm in size. Perhaps the young teacher didn't have his units correct. People often don't believe me when I tell them that the floppy disc actually hails back to the 1950s. But it does and was not used for digital recording. --Chuck