Cits 14

Front 1

What is memory management?

Back 1

Memory allocation to processes, ensuring instructions and data are available in RAM as needed

Front 2

Summarise the FIVE main requirements of memory management.

Back 2

Relocation, Protection, Sharing, Logical & Physical organisation.

Front 3

Why does memory management need to determine where instructions and data are located?

Back 3

So requests can be translated into physical addresses

Front 4

What is meant by 'protection'?

Back 4

Prevention of interference from other processes.

Front 5

How does memory management protect processes?

Back 5

By checking that memory references made by a process lie within its allocated bounds.

Front 6

When are memory reference checks made?

Back 6

At run-time

Front 7

When is an Access Violation Interrupt generated?

Back 7

When processes request invalid references

Front 8

Are the memory checks carried out by the OS or CPU?

Back 8

The CPU - software cannot inticipate all memory references to be made by a program

Front 9

What is 'shared' between processes?

Back 9

Memory

Front 10

When might sharing be necessary?

Back 10

When multiple processes are running the same program

Front 11

What permissions are applied to shared instructions?

Back 11

Read & Execute Only.

Front 12

What is "Late Binding"?

Back 12

Where references between modules of a program are resolved at run-time

Front 13

What is an advantage of late binding?

Back 13

Modules can maintain their independence right up till runtime.

Front 14

Summarise the "Physical Organisation" aspect of memory management in one sentence.

Back 14

Moving memory between RAM and disk.

Front 15

What part of the main memory is unavailable for user processes?

Back 15

The OS partition

Front 16

What are the two types of fixed-size partitioning of main memory?

Back 16

Equal-size and unequal-size partitioning

Front 17

Give two disadvantages of using equal-size partitioning in main memory.

Back 17

i) A process's requirements may exceed partition size; ii) A small process occupies a full partition, which is wasteful and leads to internal fragmentation.

Front 18

Give two disadvantages of unequal-size fixed partioning.

Back 18

i) Either algorithm for filling leads to internal fragmentation. ii) The algorithm for minimising this requires disk swapping which is expensive.

Front 19

What is the name for NON-fixed partitioning?

Back 19

Dynamic Memory Partitioning.

Front 20

How does Dynamic partitioning give rise to external fragmentation?

Back 20

Multiple processes are allocated precisely the required portion - when these processes terminate (randomly) they leave gaps between other processes, and the partitioning ceases to be contiguous.

Front 21

Name the three algorithms for process placement in dynamic memory.

Back 21

First-fit, Best-fit, Next-fit

Front 22

Describe the 'First-fit' algorithm for allocation of dynamic memory.

Back 22

Starting from address 0, scan through the main memory until a vacant partition fits.

Front 23

Describe the 'Best-fit' algorithm for allocation of dynamic memory.

Back 23

The memory is scanned for the smallest possible block in which the process can still be placed.

Front 24

Describe the 'Next-fit' algorithm for allocation of dynamic memory.

Back 24

Scans memory from the address of the last allocated process, in a similar style to 'First-fit'.

Front 25

Define the term "Logical address".

Back 25

Reference to a memory location independent of any current assignment of data to main memory.

Front 26

Define the term "Relative address".

Back 26

Is a logical address expressed relative to a fixed logical location, such as the beginning of a process's image

Front 27

Define the term "Physical address".

Back 27

The address of the actual location in main memory.

Front 28

Define the term 'Base Register'.

Back 28

Indicates the beginning of a process's partition.

Front 29

Define the term 'Bounds Register'.

Back 29

Indicates extent of a process in a partition. Used with Base Register.

Front 30

Relative address + Base register = ?

Back 30

Physical address.

Front 31

How does memory paging reduce internal fragmentation?

Back 31

Frame is divided into small, equally-sized chunks (pages), fully occupied by the process until only the last, which is fragmented.

Front 32

What is a 'page'?

Back 32

A small, equally-sized chunk of memory in a frame.

Front 33

What is a 'frame'?

Back 33

The larger chunks of main memory comprised of pages.

Front 34

Why don't we need bounds registers for pages?

Back 34

Because they are of fixed size.

Front 35

What is a 'Page Table'?

Back 35

A set of page registers in non-contiguous memory allocation.

Front 36

What information is held by the page table?

Back 36

Frame location (physical address) for each page of the running process.

Front 37

What maintains the 'page table'?

Back 37

OS

Front 38

Where would you see a 'page number' recorded with an 'offset'?

Back 38

Logical addresses for pages in a page table.

Front 39

How long are the page number and offset?

Back 39

6-bit page number, 10-bit offset

Front 40

How is the 16-bit logical address processed by the page table in converting to a 16-bit physical address?

Back 40

Page number is processed while offset remains unchanged

Front 41

How does 'Memory Segmentation' differ from Paging?

Back 41

The chunks are not all equal in size.

Front 42

What information is held within a Segment Table?

Back 42

Length and Base of segments.

Front 43

What part of the 16-bit logical address is processed by the Segment Table in converting to a 16-bit physical address?

Back 43

The 4-bit segment number. The 12-bit offset is unchanged.