Memory Management

Question 1

Address Binding?

Answer 1

Programs on disk, ready to be brought into memory to execute form an input queue

Question 2

Logical vs Physical Address Space?

Answer 2

The concept of a logical address space that is bound to a separate physical address space is central to proper memory management

Question 3

Logical Address?

Answer 3

Generated by the CPU, also referred to as virtual addres

Question 4

Physical Address?

Answer 4

Address seen by the memory unit

Question 5

Logical Address Space?

Answer 5

Is the set of all logical addresses generated by a program

Question 6

Physical Address Space?

Answer 6

Is the set of all physical addresses generated by a program

Question 7

MMU?

Answer 7

Memory Management Unit

Question 8

What does MMU do?

Answer 8

Hardware device that at run time maps virtual to physical address.

Many methods possible, covered in the rest of this chapter.

Question 9

The user program deals with what?

Answer 9

Logical addresses it never sees the real physical addresses.

Question 10

Dynamic relocation using a relocation register?

Answer 10

Routine is not loaded until it is called
Better memory-space utilization
Unused routine is never loaded
All routines kept on disk in relocatable load format

Question 11

Contiguous Allocation?

Answer 11

Main memory must support both OS and user processes
Limited resource, must allocate efficiently
Contigous allocation is one early method

Question 12

Main memory two partitions?

Answer 12

Resident operating system
User processes then held in high memory
Each proces contained in a single contiguous section of memory

Question 13

Different Registers?

Answer 13

base register contains value of smallest physical address.

Limited register contains range of logical addresses each logical address must be less than the limit register

Question 14

Multiple-Partition Allocation?

Answer 14

Degree of multiplrogramming limited by number of partitions
Variable-partition sizes for efficiency
Hole - block of available memory; holes of various size are scattered through memory
When a process arrives, it is allocated memory from a hole large enough to accomodate it

Question 15

Dynamic Storage-Allocation Problem?

Answer 15

First-fit: Allocate first hole that is big enough
Best-Fit: Allocate the smallest hole that is big enough, must search entire list, unless ordered by size.
Worst-Fit: Allocate the largest hole, must also search entire list.

Question 16

Fragmentation?

Answer 16

External Fragmentation

Internal Fragmentation

Question 17

External Fragmentation?

Answer 17

Total memory space exists to satisfy a request, but it is not contiguous

Question 18

Internal Fragmentation?

Answer 18

Allocated memory may be slightly larger than requested memory, this size difference is memory internal to a partition, but not being used.

Question 19

How do you reduce external fragmentation?

Answer 19

Compaction
Shuffle memory contents to place all free memory together in one large block
Compaction is possible only if relocation is dynamic, and is done at execution time.

Question 20

Segmentation?

Answer 20

Memory-Management scheme that supports user view of memory

A program is a collection of segments

Question 21

What is a segment?

Answer 21

Segment is a logical unit such as:
Main program
Procedure
Function
Method
Object
Local vars, Global Vars

Question 22

Segmentation Architecture?

Answer 22

Logical address consists of a two tuple

segment number, offset

Question 23

Segment Table?

Answer 23

Maps two dimensional physical addresses

Question 24

Each Segment Table has?

Answer 24

base - contains the starting physical address where the segments reside in memory
limit - specifies the length of the segment

Question 25

STBR?

Answer 25

Segment-Table base Register

Points to segment table’s memory location in memory

Question 26

STLR?

Answer 26

Segment-Table Length Register

Indicates number of segments used by a program

Question 27

Paging?

Answer 27

Physical address space of a process can be noncontiguous; process is allocated physical memory whenever the latter is available

Question 28

Paging frag?

Answer 28

Avoids external fragmentation

Avoids problem of varying sized memory chunks

Question 29

Paging, frame, page?

Answer 29

Dividing physical memory into fixed-sized blocks called frames

Divide logical memory into blocks of the same size called pages.

Question 30

Address Translation Scheme?

Answer 30

Page Number (p)
Page Offset (d)

Question 31

Page Number?

Answer 31

Used as an index into a page table which contains base addresses of each page in physical memory

Question 32

Page Offset?

Answer 32

Combined with base address to define the physical memory address that is sent to the memory unit

Question 33

What is ARM?

Answer 33

Dominant mobile platform chip.

Modern, energy efficient, 32-bit CPU