Type 270 disk file on PDP-6

Rich Alderson RichA at LivingComputerMuseum.org
Mon Mar 14 14:05:31 CDT 2016

From: Eric Smith
Sent: Saturday, March 12, 2016 8:52 PM

> I just was looking at the I/O device code assignments in the 1973
> DECsystem-10 System Reference Manual, and happened to notice the entry
> for the Type 270 disk file used on the PDP-6.

> PDP-6 and PDP-10 device codes are three octal digits, of which the
> third digit can only be 0 or 4.

> The device code for the Type 270 is octal 270.  Coincidence?  :-)

Probably.  Kind of.  More or less.

The disk file is called a 5022.  The 270 is the disk file *control*, and
yes, it has device code 270, but it attaches to the data control type 136
(device code 200).  Other things connecting to the 136 are the microtape
control type 551 (device codes 210 and 214) and the magnetic tape control
type 516 (device codes 220, 224, and 230).

Device codes were assigned sequentially, and the disk file control was
not originally part[1] of the PDP-6 system, so it probably just got the
next number available.  That some wag decided to use that as the type
number was more or less likely when it came down the pike.


[1] Based on the fact that it was built using Flip Chips, initially
    invented for the PDP-7, rather than System Modules (either the kind
    used in the PDP-1, PDP-3,[2] PDP-4, and PDP-5, or the extended kind
    invented for the PDP-6).

[2] Remember that while DEC did not build a PDP-3, a customer rumored to
    have been a front for the NSA did.  DEC sold designs as well as actual
    hardware in the early days.

Rich Alderson
Vintage Computing Sr. Systems Engineer
Living Computer Museum
2245 1st Avenue S
Seattle, WA 98134

mailto:RichA at LivingComputerMuseum.org


More information about the cctech mailing list