DEC KM11 (Was: DEC KL11)

Chris Zach cz at
Thu Sep 23 21:50:13 CDT 2021

> My notes (from sources unknown) say (of the ML11A):
>      solid-state (ram) disk; 2MB/s xfer
>      1-31 arrays of 512 or 2048 blocks ea
>      using 11/70 MK11 (MOS) memory
>      looked like RS03/RS04 to s/w

Ok, that makes sense.

> says about *REAL* RS03/04 drives:
>          "basic format was 18-bit words
>          (for use in PDP-10 and PDP-15 machines)"
> But I doubt that anyone would care to replicate THAT feature
> (throwing away two bits of each word) on a PDP-11 option!

Well, that would otherwise have been used for Massbus parity. The number 
of bits on the drive stayed the same, it's just that the formatter would 
either format the disk for 512 or 576, then use the top two bits either 
for parity or the last 2 data bits.

The other fun question that I have to figure out is can an RM80 be run 
in 18 bit mode. I'm guessing it can as it uses the same Massbus 
formatter as the RM02/03/05. Need to roll that thing out of my son's 
closet when he moves out and see what happens...


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