Week 5-6

Question 1

How does the MMU communicate to RAM and the CPU

Answer 1

CPU > Logical address > MMU > physical address > RAM

Question 2

Main memory is divided into what two parts?

Answer 2

Operating system space and User memory

Question 3

What are holes and why do they happen when we talk about continuous allocation?

Answer 3

• Holes are parts of the memory that are not allocated to a process, they happen when processes get allocated and then quit

Question 4

What are the three general approaches to storage allocation

Answer 4

• First fit - Use the first hole that is big enough
  
  • Best fit - use the smallest block that is big enough
  • Worst fit - use the biggest block

Question 5

When does fragmentation happen?

Answer 5

• Happens when there are small spaces in memory left over from allocation

Question 6

What is the difference between static and dynamic linking?

Answer 6

Static linking is when modules are linked at compile time (shared libraries are pre-allocated)
Dynamic linking is when modules are linked as needed in the operating system (Shared libraries are actually shared, OS must be prepared for this)

Question 7

What is a Overlay and what is swapping?

Answer 7

Overlay: When only needed instructions are kept in memory so when more memory is needed it takes over an older instruction that isn’t used
Swapping: When a process is moved to a backing store (hard drive) for use later.

Question 8

The point of using pages and frames is to:

Answer 8

map memory

Question 9

Physical memory is divided into _______ (512 bytes to 8K sizes typically)
Logical memory is divided into _______ (512 bytes to 8K sizes typically)

Answer 9

Frames

Pages

Question 10

An address from a page table is divided into what two parts?

Answer 10

• Page number (index of a page table)

* Page offset (location within the page)

Question 11

Does each process have a page table? (T/F)

Answer 11

(True)

Question 12

What keeps track of allocated and free frames?

Answer 12

Frame table

Question 13

What is a TLB and why is it used?

Answer 13

• translation look-aside buffer

* Maps pages to frames in the MMU

Question 14

Do pages need to = frames?

Answer 14

NO

Question 15

What is demand paging?

Answer 15

When pages of data are not copied from disk to RAM till then are really needed.

Question 16

What is copy on write?

Answer 16

data blocks on disk are allocated copy-on-write; as long as there are no changes, you keep the original blocks; a change changed only the affected blocks. Everyone has a single shared copy of the same data until it’s written, and then a copy is made. Used by the fork process.

Question 17

What is a dirty bit?

Answer 17

It is when a page has been changed. OS only writes to dirty pages