MEM11 Status Update

js at js at
Wed Sep 2 13:33:23 CDT 2015

>>>>>   run Unix V1
>>>> I am very interested in the MEM11 
>>>> for this exact reason.  I have a
>>>> PDP-11/20 that I'd love to do this 
>>>> with.  [Ethan Dicks]
>>> You could also try Mini-Unix on your 
>>> 11/20, which might support a wider 
>>> range of devices.  [Jay Jaeger]
>> Very interesting.  Does Guy's MEM11 
>> provide what's needed for Mini Unix 
>> without having to write special 
>> drivers?  [John S.]
> Not sure what Mini-Unix requires 
> w.r.t. devices.
> TTFN - Guy

I think Jay might know, but I copied and 
pasted the following paragraphs from 
some info I collected on Mini Unix:

"The normal configuration for MX 
includes a PDP-11/10 CPU with 28K words 
of memory and two RK05 disk cartridges 
for secondary. The PDP-11/10 processor 
is slower than the PDP-11/40 processor 
and does not have the full instruction 
set of the PDP-11/40 processor, thus 
requiring the emulation of the missing 
instructions. A typical C compilation 
requires about twice the total time of 
that required on the equivalent 
PDP-11/40 configuration. However, 
response to the editor commands is not 
significantly longer than on a more 
powerful CPU. The cost of a minimum 

     PDP-11/10 CPU
     28K words memory
     2 RK05 disk drives
     KL11 interface to control console
     DL11E interface to dial-up line
     60 cycle clock

is of the order of $20,000 at today's 
prices (December 1976). This provides an 
inexpensive tool for software 
development in a UNIX time-sharing 
environment for those configurations 
which have insufficient hardware to 
support a full Version 6 UNIX system."

"The MINI-UNIX system runs on any PDP-11 
processor with 28K words of memory. The 
PDP-11 computer is a 16-bit word 
mini-computer with a UNIBUS for 
interfacing DEC peripherals to the CPU. 
The typical configuration consists of a 
PDP-11/10 CPU with 28K words of memory, 
a console terminal and an RK05 
moving-head disk controller with two 
removable disk cartridges for swapping 
and file system storage. Each RK05 disk 
pack has 2.5 Megabytes (8-bit byte) of 
storage. However, the MX system also 
supports the RF fixed-head disk (1 
Megabyte) and the RP03 and RP04 
moving-head disk controllers with 40M 
bytes and 80M bytes, respectively. Other 
peripherals supported include 
line-printer, Dectape, magtape and 
various asynchronous and synchronous 
interface units.

The system is normally configured to be 
12K words in size. This includes an 
emulation package for interpreting the 
10 extended instructions normally 
performed by the EIS hardware available 
as an option on some PDP-11 processors 
and standard on the PDP-11/45 processor. 
A minimum system has room for 6 or 7 
system buffers. As new drivers are added 
to the system, the number of system 
buffers must be decreased if the system 
size is maintained at 12K words. Thus it 
is recommended that for some 
applications it may be appropriate to 
add the drivers for only a few 
peripherals on any one version of the 
system and thus maintain a few versions 
of the system, one for each set of 
drivers desired concurrently in the 
system. This keeps the system size at 
12K words in order to be able to support 
all of the user software of Version 6 UNIX."

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