Operating Systems

================ Start Lecture #17 ================
  1. Lab 2 extended on week. Due 1 april.
  2. Office hour thursday (25 mar) moved to 3:30-4:30.
  3. I did not have internet access while away and just came in via red eye so have not read email.

**4.1.2: Multiprogramming with fixed partitions

Two goals of multiprogramming are to improve CPU utilization, by overlapping CPU and I/O, and to permit short jobs to finish quickly.

4.1.3: Modeling Multiprogramming

Homework: 1, 2 (typo in book; figure 4.21 seems irrelevant).

4.1.4: Analysis of Multiprogramming System Performance


4.1.5: Relocation and Protection

Relocation was discussed as part of linker lab and at the beginning of this chapter. When done dynamically, a simple method is to have a base register whose value is added to every address by the hardware.

Similarly a limit register is checked by the hardware to be sure that the address (before the base register is added) is not bigger than the size of the program.

The base and limit register are set by the OS when the job starts.

4.2: Swapping

Moving the entire processes between disk and memory is called swapping.

Multiprogramming with Variable Partitions

Both the number and size of the partitions change with time.

Homework: 3