mixed media on Massbus [was RE: flash (or ide) storage for unibus 11?] - test-drb@ccmp.vtda.org

23 Nov 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. 
    [snip]

...
 > 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

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

mailto:RichA at LivingComputerMuseum.org

http://www.LivingComputerMuseum.org/