5

Question 1

Protection

Answer 1

-process can only access addresses in its address space
-using a pair of base and limit registers

Question 2

modes for our cpu

Answer 2

user mode, kernal mode

Question 3

address protection

Answer 3

cpu must check every memory access generator in user mode to ensure its between base and limit for that user
-instructions to load base and limit registers privileged

Question 4

Address Binding

Answer 4

Program on disk ready to be brought into memory to execute form an input queue
-source code adresses symbolic
-compiled code bind to relocatable addresses
-each binding step maps one address space to another

Question 5

Logical address

Answer 5

generated by the CPU, aka virtual address, address space is set of all logical addresses generated by a program

Question 6

physical address

Answer 6

address seen by memory unit, address space is set of all physical address space generated by a program

Question 7

Fragmentation - external

Answer 7

External - total memory space may exist to satisfy a request, not contagious. approaches like compaction - shuffle memory contents to put free memory next to each other

Question 8

Fragmentation - Internal

Answer 8

allocated memory may be larger than requested memory, size difference is memory internal to a partition, but not being used - both internal and external wasteful - paging better

Question 9

Paging

Answer 9

Physical address space of a process can be noncontiguous, process allocated physical memory where available
- avoids extermal fragmentation
- avoids problem of varying sized memory chunks

Question 10

whats pages divided into

Answer 10

fixed size blocks called frames, size is power of 2 between 512 bytes and 16Mb

Question 11

To run a program of N pages how many frames we need

Answer 11

N

Question 12

address translation scheme

Answer 12

divided into page number - index into page table which contains base address of each page in physical memory
page offset - combined with base address to define physical memory

Question 13

where is page table

Answer 13

kept in main memory
-PTBR Page-table base register points to the page table
PTLR Page table length register indicates size of page table

Question 14

Translation Look-Aside Buffer

Answer 14

Store adress-space identifers in each TLB entry, these uniquely identify each process to provide address-space protection

Question 15

effective access time

Answer 15

Hit ratio - percentage of times page number found in TLB

Question 16

Shared pages

Answer 16

one copy of read-only code shared among processes
each process keeps separate coipy of code and data

Question 17

Structure of page table

Answer 17

-Hierarchial Paging
-Hashed Page Tables
-Inverted Page tables

Question 18

Hierarchical page tables

Answer 18

Break up logical address space into multiple page tables
two level page table

Question 19

Hashed page tables

Answer 19

common in address spaces > 32
page number hashed into page table

Question 20

swapping

Answer 20

process can be temporarily swapped out of memory to a backing store, then brought back into memory

Question 21

backing store

Answer 21

fast disk large enough to accomodate copies of all memory images for all users
system maintains a ready queue of processes have memory images on disk