mixed media on Massbus [was RE: flash (or ide) storage for unibus 11?]

Rich Alderson RichA at LivingComputerMuseum.org
Mon Nov 23 15:54:23 CST 2015

From: Paul Koning
Sent: Monday, November 23, 2015 11:26 AM

>> On Nov 23, 2015, at 1:00 PM, Johnny Billquist <bqt at Update.UU.SE>> wrote:

>> As far as I can tell, disks fall into two groups, as far as massbus control
>> is concerned. The RM02, RM03, RM05, RM80 and RP07 is one group.  The RP04,
>> RP05, RP06 is another. A few register addresses between the groups are the
>> same, but the actual register at that address is different. But if I
>> remember right, it's registers that have to do with error recovery, so
>> potentially not something people would care about in emulation anyway. But
>> it still means there are different drivers in the OS for them.


>> And of course, you also have the TM02/TM03 and TM78, which have yet again
>> different registers on the massbus.

> Yes.  And mixing disk and tape on a massbus is something that I don't think
> was done on PDP-11s.  It certainly could have been done, and it was on VMS
> and/or TOPS if I remember right.

Two things.

1) There is not such things as "TOPS".  The 2 operating systems for the PDP-10
   provided by DEC are Tops-10 and TOPS-20.  The only thing they have in common
   is the first 4 letters (modulo case) of the names.  They share exactly no
   code in the monitor ("kernel"), and do not even have the same origins.

   Tops-10 started as the monitor on the PDP-6, in 1964, and was in continuous
   development until 1988 (and in maintenance until 1993+), while TOPS-20 began
   life as the TENEX operating system from BBN c. 1969, licensed for the new
   KL-10 processor while that was under development.  TOPS-20 v1 appeared in 1975.

   BBN developed a run time  package for TENEX called PA1050 which handled a
   subset of the Tops-10 system calls by merging into user-mode programs and
   intercepting them; DEC carried on the same mechanism to allow Tops-10 compilers
   and other utilities to run on the new OS while native versions were developed.

2) Having stated all that, Tops-10 does not allow mixing tapes and disks on a
   channel, but it does allow mixing disk drive types.  TOPS-20 has always
   allowed mixing tapes and disks on a channel.


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

mailto:RichA at LivingComputerMuseum.org


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