memory protection

Question 1

how does base and limit work

Answer 1

each process has a base and limit for the memory addresses its allowed to access
whenever we want to go to memory to access something we check that the address is between the base and limit

Question 2

what is a benefit of base and limit

Answer 2

easy to handle as we just need two registers one for the base and one for the limit

Question 3

logical address

Answer 3

the address that the program is written to/ the process sees

Question 4

physical address

Answer 4

where the process is actually stored

Question 5

in base and limit how do we calculate the physical address

Answer 5

base + logical address

Question 6

what is a negative of base and limit

Answer 6

we assume that programs start at 0 in memory so depending on when the process is loaded youll get a different set of memory addresses for it and wont know what the values will be

Question 7

relative addressing

Answer 7

writing programs so memory access is relative to the memory address

Question 8

what is a negative of relative addressing

Answer 8

awkward and messy

Question 9

in which two ways can we solve the problem of base and limit making programs start at an arbitrary value

Answer 9

relative addressing
dynamically remapping addressing from logical to physical

Question 10

what does the memory management unit do

Answer 10

contains the mappings
contains the logic for checking if an address is valid

Question 11

how does the mmu get the correct address and what does it do if the address is incorrect

Answer 11

we check if the logical address is less that the limit
if so we add the base value and that gives us an address within the process
if its > or == the limit then we get an address error

Question 12

how does segmentation work

Answer 12

logical addresses are stored as the segment number and the offset
the segment number is the index of the segment descriptor table which gives us the base address and the limit
we check if the offset is < the limit
if yes then we add the offset to the base to give us the physical address

Question 13

what is a positive of segmentation

Answer 13

provides protection to processes and the segments allowing us to have different permissions per segment

Question 14

segment

Answer 14

the logical elements that a process can be broken into which can have different permissions

Question 15

segment descriptor table

Answer 15

stores the base and limit of each segment

Question 16

segment number

Answer 16

index for the segment descriptor table

Question 17

what does paging do to memory

Answer 17

divides it into blocks

Question 18

what are two benefits of paging

Answer 18

memory is now in blocks making it easier to manage
makes memory management more flexible and efficient

Question 19

page

Answer 19

logical block

Question 20

frame

Answer 20

physical block

Question 21

page number

Answer 21

index for page table

Question 22

page table

Answer 22

maps a logical page to a physical frame

Question 23

what does the logical address for paging contain

Answer 23

the page number and the offset

Question 24

how does paging work

Answer 24

the logical address points to the page in the page table which maps to the frame in memory
the offset is used to find the specific byte needed in that page

Question 25

how does shared memory work with paging

Answer 25

different virtual addresses can have the same frame therefore both processes are communicating with the same block

Question 26

what is a benefit of shared memory and paging

Answer 26

can access the same block allowing things like shared libraries

Question 27

how does paging make memory management more efficient and flexible

Answer 27

translation allows two processes to have the same logical address but map to different physical addresses therefore it looks like we have more space available as we can swap pages between the disk and memory