Lecture 15

Question 1

Function of operating system

Answer 1

“Middleman” to run your executable codes on the computers.

Need to put your programs into the physical memory space before they are run by CPU.

Question 2

How to manage programs

Answer 2

The first approach: simply allocate them
based on the size of program code (called
“process” in OS)
Eventually see “holes” scattered in different places

Question 3

Paging system

Answer 3

Divide the physical memory space into pages.

Question 4

First-fit Strategy

Answer 4

Allocate the FIRST hole that is big enough

reason: simple

Question 5

Best-Fit Strategy

Answer 5

Allocate the SMALLEST hole that is big enough

reason: produce the smallest left-over hole

Question 6

Worst-Fit Strategy

Answer 6

Allocate the LARGEST hole

reason: produce the largest left-over hole

Question 7

External Fragmentation

Answer 7

Total free-memory exists to satisfy a request, but it is not contiguous
(solution: compact the free memory into one contiguous space)

Question 8

Internal Fragmentation

Answer 8

Part of the nature in the paging system

solution: use smaller page size

Question 9

How to manage memory with a Linked List and keep track of all allocated and free memory pages

Answer 9

–When a request (called “job” in OS) comes, use the specific strategy to find the “hole”
–Allocate the free-memory pages to the allocated-memory pages
–Update BOTH linked lists
–Calculate the fragmentation
–Do the compaction if necessary