UNIX on PDP 11/23s

[BonnellDS]

     About a week ago a request was made for information on UNIX and UNIX like
operating systems for the PDP 11/23 or 11/23+. I would like to recommend the
UNIX lookalike operating system marketed by Venturcom, VENIX/11. I have used
this operating system on several 11/23 systems, and have not been disappointed
with the performance or abilities of VENIX/11.

     VENIX/11 is a mixture of V6, V7 and Berkley UNIX. The filesystems are
formated in the V6 style, with inodes of 32 bytes each instead of the V7 style
of 64 bytes each. This difference is only of concern at boot time, file
transfers can be handled by 'tar' or some other utility that uses it's own
file format.

     VENIX/11 has it's kernel code re-written from 'C' source to PDP11 
assembler. This has the advantage of producing a small (56KB) and fast kernel,
but source is not available from Venturcom. I have seen several schemes used
to 'overlay' the various sections of standard V7 UNIX on an 11/23. They all
have performed poorly in terms of execution speed and certain versions had
trouble with the memory management, causing very strange crashes!

     VENIX/11 allows the user to 'lock' I/O intensive processes in memory for
'real time' performance.

     The utilities provided with VENIX/11 are fairly complete. The 'vi' editor
is not available, since 'vi' requires a lot of memory space for data and the
11/23 does not have separate I and D space. The screen editor supplied with
VENIX/11 is called 'ice'. This is a simple editor that expects a VT-52 type
terminal. The source for 'ice' is part of the VENIX/11 distribution package,
so modifications could be made for use with other terminals.

     Source is provided for a large range of standard DEC peripherals, RL/RK
disk drives, DL and DZ serial boards, etc. Source is also provided for
c.c (device switch table) and l.s (interrupt vectors). Since the person who
requested this information mentioned that the system would be used at home,
I would recommend investigating using VENIX/11 with a non DEC standard disk
system. I have source for a disk driver that is based upon the Data
Technologies SASI interface and ST-506 disk controllers for the LSI 11. A
20 MB disk subsystem could be constructed for about $1800. The DTC boards are
available from Shugart through Hamilton Avnet. I paid $550 for the set that
I am currently using.

     Certain of the utility programs that are dependant on the filesystem
layout have names that are different from V7. As an example, 'fsck' on V7
expects V7 filesystems (not V6) and uses the kernel file '\unix' for info
of the filesystems to be checked. The VENIX/11 version of this utility is
called 'fcheck', and uses the kernel file '/venix'. I consider these minor
variations on the utility names to be only a minor inconvienience. It does
make it clear which utilities have been changed, however.

     While the VENIX/11 package can be purchased directly from Venturcom, 
the price is in the $2000 range. Cambridge Digital was willing to sell the
package to my former employers for around $1200. This price may or may not
be discounted because of the purchase of the hardware along with VENIX/11.

     Of course, the above thoughts are purely my own and do not reflect
the feelings of my current or past employers in any way. Some of the words
I have used that cannot be found in a dictionary, and all of the words in
uppercase, are trademarks of assorted companies.

					Douglas Bonnell
"the problem's plain to see,
 too much technology"