Operations Systems C2

Question 1

What is the critical aspect of main memory management?

Answer 1

Main memory management is critical for the entire system’s performance

Question 2

On what two items does the entire system performance depend?

Answer 2

The entire system performance depends on the amount of memory available and the optimization of memory during job processing

Question 3

What are the four types of memory allocation schemes introduced

Answer 3

The four types of memory allocation schemes introduced are

Single-user systems,

Fixed partitions,

Dynamic partitions,

Relocatable dynamic partitions

DR SF

Question 4

Describe the Single-User Contiguous Scheme

Answer 4

Loads the entire program into memory
contigious memory space is now been allocated so that the job(s) can be processed

Question 5

What are the disadvantages of the Single-User Contiguous Scheme?

Answer 5

The disadvantages include lack of support for multiprogramming or networking and being cost-ineffective, making it unsuitable for business when introduced in the late 1940s and early 1950s

lack of surport for
multiprogramming
network
and cost in-effective

Question 6

How does Fixed Partitions permit multiprogramming?

Answer 6

Fixed Partitions permit multiprogramming by by dividing main memory, with each partition dedicated to one job.

Question 7

What are the responsibilities of Fixed Partitions in memory management?

Answer 7

Fixed Partitions are responsible for protecting each job’s memory space and matching job size with partition size

Protecting jobs mem space

job size —>{match} partition size

Question 8

What are the characteristics of Fixed Partitions?

Answer 8

Fixed Partitions load the entire program side by side, and job allocation involves choosing the first available section of the Right size.

Question 9

What is the main characteristic of Dynamic Partitions in memory management?

Answer 9

Dynamic Partitions allocate memory by creating sections in main memory, providing each job with space as needed.

Question 10

What are the disadvantages of Dynamic Partitions?

Answer 10

Disadvantages include full memory utilization only when the first jobs are loaded, subsequent allocation leading to memory waste, and external fragmentation between blocks.

you need to have full mem only when the first job is loaded
and you need to allocate mem waste and external fragmentation bet blocks

Question 11

What are the two methods for free space allocation in memory management?

Answer 11

The two methods are First-fit memory allocation and Best-fit memory allocation

Question 12

How does the First-fit memory allocation method work?

Answer 12

In First-fit memory allocation, the Memory Manager organizes free/busy lists by memory locations, and a job is assigned the first partition large enough for fast allocation

organizes free/busy list by memory locations

jobs are assigned to the first parition large enough

resulting in memory waste but fast allocation

Question 13

What are the advantages and disadvantages of First-fit memory allocation?

Answer 13

The advantage is faster allocation, but the disadvantage is memory waste

Question 14

How does the Best-fit memory allocation method differ from First-fit?

Answer 14

In Best-fit memory allocation, free/busy lists are ordered by size, and a job is assigned the smallest partition large enough, reducing wasted space and internal fragmentation.

orgainizes free/busy list by size
and jobs are assigned to the smallest partition to accomindate it

resulting in reducung the memory watage and inter fragmentation but slower in performance wise

Question 15

What is the goal of the Best-fit algorithm?

Answer 15

The goal is to find the smallest memory block where the job fits, with the entire table searched before allocation.

Question 16

What is deallocation in memory management?

Answer 16

Deallocation involves releasing allocated memory space.

Question 17

How does deallocation work for fixed-partition systems?

Answer 17

In fixed-partition systems, the Memory Manager resets the job’s memory block status to “free” upon job completion, using any code (e.g., 0 = free and 1 = busy).

Question 18

What is the algorithm for deallocation in dynamic-partition systems?

Answer 18

The algorithm in dynamic-partition systems tries to combine free areas of memory, and it involves three cases depending on the position of the block to be deallocated.

Question 19

What are the three dynamic partition system cases for deallocation?

Answer 19

• Case 1: The block is adjacent to another free block.
  • Case 2: The block is between two free blocks.
  • Case 3: The block is isolated from other free blocks.

Question 20

Describe Case 1 where two free blocks are joined

Answer 20

: In Case 1, adjacent blocks are joined, and the list changes to reflect the starting address of the new free block. The memory block size changes, showing the new size for the free space, resulting in two free partitions.

in simple terms, Case 1 involves putting together neighboring free blocks to make a bigger one. The system’s list gets updated to show where this bigger block starts( starting address ), and its size is adjusted accordingly. This results in having two free partitions turning into one larger free partition

Question 21

Explain Case 2 where three free blocks are joined.

Answer 21

In Case 2, deallocated memory space is between two free memory blocks. The list changes to reflect the starting address of the new free block, and three free partitions’ sizes are combined. The total size is stored with the smallest beginning address, and the last partition is assigned null entry status.

In Case 2, we merge three free blocks by updating the list with the new starting address. The sizes of the three free partitions are combined, and the total size is stored with the smallest beginning address. The last partition is marked with null entry status.

Question 22

Define Case 3 for deallocating an isolated block.

Answer 22

In Case 3, deallocated memory space is isolated from other free areas. The system determines the released memory block status, searches the table for a null entry if the block is not adjacent to any free memory blocks between two other busy areas. The memory block between two busy memory blocks is then returned to the free list.

In Case 3, isolated deallocated memory is addressed separately. The system checks the released memory block status, searches for a null entry if it’s not next to other free blocks, and adds the block between two busy areas back to the free list.

Question 23

What does the Memory Manager do in Relocatable Dynamic Partitions?

Answer 23

The Memory Manager in Relocatable Dynamic Partitions relocates programs by gathering all empty blocks together, compacting them to make one memory block large enough to accommodate some or all waiting jobs.

Question 24

What is compaction in the context of memory defragmentation?

Answer 24

Compaction involves the operating system reclaiming fragmented memory space sections by relocating most or all programs in memory, achieving a contiguous arrangement. The operating system distinguishes between addresses and data values, adjusting every address and address reference to match the program’s new memory location while leaving data values unchanged.

Compaction is when the operating system rearranges scattered memory sections to create a continuous block. It involves relocating programs in memory, adjusting addresses to match the new locations while keeping data values unchanged.

Question 25

What are the key issues related to compaction in memory management?

Answer 25

The key issues include understanding what goes on behind the scenes during relocation and compaction, keeping track of how far each job has moved from its original storage area, and updating lists such as the Free list and Busy list

Question 26

How do special-purpose registers assist in relocation?

Answer 26

Special-purpose registers, such as the Bounds register storing the highest location accessible by each program and the Relocation register containing the adjustment value added to each address referenced in the program, help with relocation. The adjustment value is zero if the program is not relocated.

Special registers, like the Bounds register and Relocation register, help move programs to the right place in the computer’s memory. The Relocation register has a number that gets added to addresses in the program, making sure everything is in the correct spot. If a program doesn’t need to move, the adjustment value is zero.

Question 27

What is the goal of compacting and relocating in memory management?

Answer 27

The goal is to optimize memory use, improve throughput, and keep overhead as low as possible. Compaction timing options include when a certain memory percentage is busy, when there are waiting jobs, or after a prescribed time period has elapsed

The aim is to make the computer use its memory in the best way, work faster, and not waste too much extra time. Compaction, which is like cleaning up the memory, can happen when a lot of the memory is being used, when there are jobs waiting to be done, or after a certain amount of time has passed.

Question 28

What are the four memory management techniques discussed in the conclusion?

Answer 28

The four memory management techniques mentioned in the conclusion are Single-user systems, fixed partitions, dynamic partitions, and relocatable dynamic partitions.

Question 29

What is common to all four memory management techniques?

Answer 29

Common to all four techniques is that the entire program is loaded into memory, stored contiguously, and resides in memory until completed.

Question 30

What restrictions do all schemes place on job size?

Answer 30

All schemes place severe restrictions on job size, which are limited by the largest partition.

Question 31

What is bounds register in relocation dynamic scheme

Answer 31

ensures that the program doesnt hvae access to other memory

Question 32

what is bounds regsiter in relocatable dynamic partition schemme

Answer 32

it ensures that the excecution of a program doesnt get access to other memory locations