Section 15.5
Operating Systems
15.5 Memory Management
15.5.1 Fixed Partitions
In early multi-programming systems the main memory was divided up into a number of fixed sized
partitions.
Each partition held a single job. A job can only be in one partition.
15.5.2 Virtual Memory (Virtual Storage)
Proccesses to be run are held on disk. While a proccess gets CPU time the OS transfers the correctly
running proccess to disk and the next proccess to memory.
Paging
Data is transferred between memory and disk. Paging means that a fixed number of bytes is swapped
between disk and main memory.
The operating system has to keep track of where the parts of a program are at any given moment.
For each running process, the OS maintains a map showing which blocks of virtual storage are currently
in real storage and their locations.
Segmentation
Programs are divided up into different sized segments which may be loaded into non-contigous areas of
memory.
