COMP 322: Chapter 6: Memory Management

Question 1

Physical memory (RAM)

Answer 1

It is a hardware structure consisting of a linear sequence of words that hold a program during execution.

Question 2

A word

Answer 2

A fixed-size unit of data.

Can be 1, 2 or 4 bytes

Question 3

Physical address

Answer 3

An integer of range [0; n-1] that identifies a word in a physical memory of size n.

The address comprises a fixed number of bits.

Question 4

Logical address space

Answer 4

An abstraction of physical memory.

Consists of imaginary memory locations in a range [0; m-1] where m is the size of the logical address space.

Question 5

Logical address

Answer 5

An integer in range [0; n-1] that identifies a word in a logical address space.

Question 6

The word size of an address space depends on ___

Answer 6

Neither the address size nor the address space size.

Question 7

Program transformations: Source module

Answer 7

It is a program/program component written in a symbolic language such as C or assembly

Question 8

Program transformations: Object module

Answer 8

It is the machine language output of the compiler.

Question 9

Program transformations: Load module

Answer 9

is a program or a combination of programs in a form ready to be loaded into main memory and executed.

Question 10

Program relocation

Answer 10

The act of moving a program component from one address space to another.

Question 11

Static relocation

Answer 11

Binds all logical addresses to physical addresses prior to execution.

Question 12

Dynamic relocation

Answer 12

Postpones the binding of a logical address to physical address until the addressed item is accessed during execution.

Question 13

Relocation register

Answer 13

Contains the physical starting address of a program or program component in memory.

Question 14

Free space management: First-fit

Answer 14

Always starts the search from the beginning of the list and allocates the first hole large enough to accommodate the request

Question 15

Free space management: Next-fit

Answer 15

Starts each search at the point of last allocation.

Question 16

Free space management: Best-fit

Answer 16

Searches the entire list and chooses the smallest hole large enough to accommodate the request.

Question 17

Free space management: Worst-fit

Answer 17

Takes the opposite approach from best-fit and chooses the largest available hole for any request.

Question 18

External memory fragmentation

Answer 18

The loss of usable memory space due to holes between allocated blocks of variable sizes.

Question 19

The 50% rule

Answer 19

If the probability of finding an exact match for a request, one third of all memory partitions to holes.

Question 20

Swapping

Answer 20

The temporarily removal of a module from memory.

The module is saved on a disk and later moved back to memory.

Question 21

Memory compaction

Answer 21

The systematic shifting of modules in memory, generally in one direction.

Question 22

Linking

Answer 22

The act of resolving external references among object modules and can be done statically, before leading or dynamically while the program is already executing.

Question 23

Sharing

Answer 23

is the act of linking the same copy of a module to multiple other modules.

It improves memory utilization by making processes share common routines or services.

Its possible under both static and dynamic linking.

Question 24

A page

Answer 24

A fixed-size contagious block of a logical address space identified by a single number. The page number.

Question 25

A page frame

Answer 25

A fixed-size contiguous block of physical memory identified by a single number, the page frame number.

It is also the smallest unit of data for memory management.

Question 26

A page table

Answer 26

It is an array that keeps track of which pages of a given logical address space reside in which page frames.

Each page table entry corresponds to one page and contains the number or the starting address of the frame containing the page.

Question 27

The size of the address space

Answer 27

2^(n)

Question 28

The size of the page size

Answer 28

2^(k)

Question 29

Components of logical address

Answer 29

It has two components:
a page number (p)
an offset w (w) within the page.

It has the form (p,w)

Question 30

Components of a physical address

Answer 30

It has two components:
A frame number (f)
an offset w (w) within the frame.

It has the form (f,w)

Question 31

Internal fragmentation

Answer 31

The loss of usable memory space due to the mismatch between the page size and the size of the program.

Creates a hole at the end of the program’s last page.

Question 32

Segment

Answer 32

A variable-size block of a logical space identified by a single number, the segment number.

Question 33

Segment table

Answer 33

An array that keeps track of which segment resides in which area of physical memory.

Each entry corresponds to one segment and contains the starting address of the segment.

Question 34

Main advantage of segmentation

Answer 34

The ability to create multiple variable-size address spaces.

Question 35

Main advantage of paging

Answer 35

The ability to place any page into any frame in memory.

Segmentation can be combined with paging.

Question 36

Segmentation with paging (structure)

Answer 36

A logical address is divided into 3 components:
a segment number (s)
a page number (p)
an offset (w) within the page.

A physical address is divided into 2 components:
a frame number (f)
an offset (w) within the frame

The OS translates logical addresses of the form (s,p,w) into the corresponding physical addresses (f,w).

Question 37

Translation lookaside buffer (TLB)

Answer 37

A fast associative memory buffer that maintains recent translations of logical addresses to frame in physical memory for faster retrieval.

Question 38

Principle of locality

Answer 38

states that locations accessed recently are more likely to be accessed again then other locations accessed in the distant past.

Question 39

TBL”s hit ratio

Answer 39

The fraction of memory accesses that find a match in the TLB.