Module 7.1.3 - Dynamic, Variable-sized Partitioning

Vocabulary and key concepts regarding dynamic memory partitioning, allocation policies, and address translation.

Dynamic, variable-sized partitions

A memory management technique where partitions are created dynamically based on process data size, meaning the number and lengths of partitions change over time.

Free space

Also known as a "hole," this refers to un-partitioned memory or gaps between partitions that occur as processes are swapped in and out of main memory.

External fragmentation

The condition where memory ends up with various free spaces or holes between partitions as processes are swapped in and out.

Linked list of free spaces

A mechanism to keep track of free spaces where each list element stores a base address and the size of that free space.

First fit (FF)

A partition placement policy that scans the list and chooses the first free space large enough for the partition; it is simple and fast but may crowd the initial regions of memory.

Next fit (NF)

A partition placement policy similar to First fit, but the scanning starts where the previous scan ended to provide more distributed allocation.

Best fit (BF)

A partition placement policy that scans the entire list and chooses the smallest free space that is large enough; it is slow and can leave many small unusable free spaces.

Worst fit (WF)

A partition placement policy that scans the entire list and chooses the largest free space that fits the process, leaving larger free spaces but being slow to execute.

Logical address

An offset relative to a start address of $0$ used by a program during execution.

Logical address space

The range of logical addresses available for a specific process.

Physical address

An absolute address in memory generated by the system after translating the relative offset.

Physical address space

The range of absolute addresses occupied by a process in main memory.

Base address and limit

Values maintained by the system to translate a logical address into a physical address by adding the base address to the offset and checking if the result is within the partition limit.

Partition relocation

The ability to map a process to different physical partitions over time, which is made possible through the use of relative addressing.