Memory Management (week 8)

Question 1

what are the 2 types of memory in the computer system

Answer 1

primary memory and secondary memory

Question 2

primary memory holds __________

Answer 2

information while the CPU is using it

Question 3

secondary memory stores ___________

Answer 3

information in storage devices while CPU is NOT using it

Question 4

who is responsible for allocating and deallocating primary memory

Answer 4

memory manager

Question 5

memory manager ensures that the memory is _______________

Answer 5

not abused and is used efficiently.

Question 6

system calls with respect to the use of memory is found in ________ os

Answer 6

windows and unix

Question 7

what are the requirements of memory manager

Answer 7

–> Minimize executable memory access time

–> Maximize executable memory size

–> Executable memory must be cost effective

Question 8

what does the memory manager do ?

Answer 8

–> Allocates primary memory to processes
–> Maps process address space to primary
memory
–> Minimizes access time using cost-effective memory configuration
–> May use static or dynamic techniques

Question 9

how is it like at the top and bottom of the storage hierarchy

Answer 9

At the top of the hierarchy is faster, but more expensive memory, e.g., registers (more frequently used)

At the bottom is slower, but cheaper memory, e.g., hard disk, tape drives. (less frequently used)

Question 10

why is there a need to attach addresses to every single instruction in the program When a program is converted (compiled)
into executable form

Answer 10

–> Program instructions need to be stored in a particular order in order for the CPU to execute in the correct way.

–> Programs involve many ‘jumps’ to different parts of the program. In order to do this, there has to be a concept of addresses for every part of the program.

Question 11

what is address binding

Answer 11

the process of attaching addresses to every single instruction of the program when the program is being compiled into executable form is called address binding

Question 12

how to create an executable program

Answer 12

–> compile time: source code is converted to object code

–> link time: after compilation, there is a need to link it with the libraries. This executable file is stored in secondary storage devices

–> load time: When the executable file is run it is loaded into the RAM, where primary memory is allocated then the addresses are adjusted in address space where finally the address space is copied from secondary memory to primary memory

Question 13

what are 3 ways to ensure that when a
program is loaded up into memory, each
instruction has an address. (types of address bindings)

Answer 13

compile time binding
load time binding
run time binding

Question 14

how does compile time binding work ?

Answer 14

–> Addresses are attached to each instruction when program is compiled.

–> Program is loaded into same location in
memory whenever it is executed.

–> Cannot be relocated into different locations in memory.

–> good for single memory systems like ms dos

Question 15

what is load time binding

Answer 15

–> During compilation, the program is attached with relocatable addresses. E.g., start at 0x0000.

–> When program is loaded into memory, the location of the first instruction is loaded into a special register

–> To access the program, take re-locatable address of instruction + value of special register

–> Once loaded into memory, the program cannot be relocated into another portion of the memory.

Question 16

what is run time binding

Answer 16

–> Address binding is delayed until run-time

–> Similar in concept to load time binding, i.e., using a relocatable register.

–> Address of instruction is calculated only when the instruction is required.

–> Very flexible as program can be relocated into any portion of memory at any time.

–> Used by modern OS for multi programming.

Question 17

what is logical address

Answer 17

it is the address which is generated by the CPU also called virtual address

Question 18

what is physical address

Answer 18

it is the address as seen by the memory unit

Question 19

when are logical addresses and compile time addresses the same

Answer 19

in compile-time and load-time address-binding schemes.

Question 20

when are logical addresses and compile time addresses different

Answer 20

differ in run-time address-binding scheme.

Question 21

set of all logical addresses is referred to as ____________

Answer 21

logical
address spaces

Question 22

set of all physical addresses is referred to as

Answer 22

physical address spaces

Question 23

what are the 3 strategies memory allocation

Answer 23

fixed partition

variable partition

Question 24

what is fixed partition

Answer 24

–> Primary memory is divided into a fixed number of fixed-size blocks/partitions

–> partitions are not of fixed size (most of the time)

–> prone to internal fragmentation

Question 25

what is variable partition

Answer 25

–> Memory is allocated to processes on a need-to and available basis

–> Use dynamically determined, variable-sized blocks

–> prone to external fragmentation

–> requires run time address binding to resolve fragmentation problems

Question 26

what is fragmentation

Answer 26

Ideally, the memory manager could allocate every single byte of memory to a process if any process needs memory.

However, in practical terms, parts of the memory, called memory fragment, cannot be used at any given time because memory manager is unable to allocate these parts in an efficient manner.

Question 27

2 types of fragmentation

Answer 27

internal fragmentation

external fragmentation

Question 28

when does internal fragmentation occur

Answer 28

Internal fragmentation occurs when memory is divided into fixed sized blocks and allocated in blocks. Leftover space within a partition after process allocation is unavailable for use until the process is completed and the memory partition is released.

Question 29

when does external fragmentation occur

Answer 29

External fragmentation is caused due to dynamic memory allocation in blocks of different sizes according to process sizes. Over time, many small separate blocks will be created due to processes being added and terminated.

Question 30

can internal and external fragmentation occur together

Answer 30

no, they are mutually exclusive

Question 31

what is compaction

Answer 31

The process of compaction combines all the free memory spaces that are left over from external fragmentation into a big block by reordering the processes. It solves the problem of external fragmentation which is the result of variable memory partitioning.

Question 32

Which address-binding method do you think a feature like compaction requires?

Answer 32

Compaction requires run time binding as processes are likely to be moved when compaction is done.

Question 33

how much is 1K

Answer 33

2^10 = 1024

Question 34

drawback of doing compaction

Answer 34

compaction costs CPU time to perform and because of this it is considered an overhead operation

Question 35

when and how often should compaction occur

Answer 35

when there are jobs waiting to get in.

after a prescribed amount of time has
elapsed and you suspect your system is in a very fragmented state.