Mini Unix

Mini-UNIX is a very cut-down 6th Edition that ran on PDP-11s without memory management. It was released in May 1977. The documentation in Mini-UNIX says:

The MINI-UNIX system running is configured to run on an PDP-11/10 with the given disk and the console teletype (KL) and using the EIS (extended instruction set) software emulation package. emul.s contains the software emulation package to handle the extended instruction set, i.e. those instructions which are not implemented in the PDP-11/20 and PDP-11/10 processor hardware.

MINI-UNIX uses 12K words of memory for the system and 16K words for user programs. Most of the MINI-UNIX software will run with 12K words of memory, but some things require much more.

MINI-UNIX only supports the 11/45 FP11-B floating point unit. For machines without this hardware, there is a user subroutine available that will catch illegal instruction traps and interpret floating point operations.

As well, the setup documentation describes the essential differences between Mini-UNIX and 6th Edition:

There are a number of differences between the capabilities of MINI-UNIX and standard UNIX of which the user should be aware. The concept of ``groups'' is not supported in MINI-UNIX; no profiling is done in MINI-UNIX; it is not possible to interactively debug another running process in MINI-UNIX. User programs are limited to 16K words in size and the sharing of text is not possible. Pipes are not implemented in the system; rather they are implemented as ``pseudo-pipes'' in the Shell command. Thus complex commands such as:

nm a.out | grep _c | pr -3

are still possible. However the commands are executed sequentially, saving data in intermediate files. The bc command, in particular, works as in the standard UNIX system but cannot be used interactively since pipes are not implemented in the system. The source for the yacc compiler has been edited to change some table sizes to make it run in 16K words of memory.