CS322: Some Typical Operating Systems: MS/DOS, VMS, and Unix

Additional Materials:

The MS/DOS Operating System

  1. A bit of history

  2. Structure: MS/DOS assumes that the underlying computer will consist of up to 640K of RAM, plus ROM that is preprogrammed by the manufacturer with drivers for the various IO devices present. MS/DOS partitions RAM into 6 regions:

  3. Interfaces:

           |  COMMAND.COM | Utilities | Applications  |
           | ---------------------------------------- |
           | |                BDOS                  | |
           | | ------------------------------------ | |
           | | |              BIOS                | | |
           | | | -------------------------------- | | |
           | | | |          Hardware            | | | |

The VMS Operating System

  1. Runs on Digital Equipment Corp VAX family, which ranges from micro-VAX to the 9000 series including multi-processor and cluster systems. Though underlying hardware varies widely, the program and user interfaces are essentially the same across the spectrum.

  2. Structure is much more complex, since VMS supports simultaneous batch, interactive (timeshared) and real-time processes, using virtual memory. We will come back to VMS at various times to illustrate these concepts. The basic memory organization looks like this to the user (but not physically, since the system uses virtual memory):

            00000000H       User program/data space - grows toward high
            ?????????       (unused)
            7FFFFFFFF       User stack space - grows toward low memory
            800000000       Operating system space - system service and
                            library routines etc.

  3. Interfaces:

The Unix Operating System

  1. Originally developed at Bell Labs in the 1970's on DEC PDP-11's. (The name is a play on the name of MULTICS - a multi-user operating system being developed at MIT.) Like VMS, Unix is a multi-user system. A distinctive of Unix is that it has been ported to a wide variety of CPU's, ranging from VAX's to micro-computers.

  2. Interfaces

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These notes were written by Prof. R. Bjork of Gordon College. In January 1998 they were converted to HTML and lightly editited by J. Senning of Gordon College.