Camexec

An ITS-style PDP-11 operating system.

Information from Mike Speciner:

It was a timesharing system with a tree of processes for each user. PDP-11 memory management was used to isolate the users and their processes. The top-level process for each user was normally [PDP-11] DDT. There were software-generated interrupts of various sorts. A process could intercept the system calls of its children or let the OS handle the calls. We used this feature to write a process that emulated DEC's DOS so that we could use DEC's code to do things like run the assembler and compilers.

As I said, there was a DOS emulator. There was a version of TECO for use as a text editor. There was stand-alone SALV to clean up the disk. Disk blocks were pre-allocated so that a crash could make some free blocks seem like they were in use; SALV fixed that. But barring bugs or hardware failures, the disk data structures wouldn't get corrupted if SALV weren't run.

There were other user programs whose identity I no longer recall. And the server for the Camex product, a newspaper display-ad makeup system, ran under the OS on a PDP-11/35. The client was a less-capable PDP-11/05--using a different miniOS and running with an Adage display system. I seem to recall using DDCMP over some weird device to communicate between client and server.

There OS had drivers for various devices, including a software device for interprocess communication. The OS did not do swapping, so everything that ran simultaneously had to fit in memory. But multiple copies of programs shared their code spaces.