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23 Cards in this Set

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What are the two main users of memory?
- OS
- Applications
What are two ways to track memory usage?
-Linked lists
-Bitmaps
What is a "Free List"?
A linked list being used for memory management.
How does a bitmap keep track of memory allocation?
- One bit per chunk.
- 1 = chunk in use
- 0 = chunk free
What is contigous memory management?
-Memory is allowcated in a contigous piece. memory for low level device i/o.
What is noncontigous memory management?
Memory not necissarily allocated in one piece.
How efficient is Contiguous memory allocation?
Since blocks may not be used up there can be small fragments left over. 110 byte allocation. 128 byte block. 18 bytes left over.
Explain best fit algorithm.
Small as possible chunk allocated.
Pros: Leaves larger blocks for future requests.

Cons
Leaves runt blocks.
Explain Worst Fit Algorithm.
Seach for the largest possible block. split it to satisfy the request.

Pros:
-Shouldn't leave as many runt blocks.

Cons:
-Slow search
-Small holes still possible
-May prevent larger allocations from being granted.
Explain first fit algorithm.
-Use the first block that is large enough to fill the request.

Pros:
-Fast search speed.

Cons:
-May unnecessarily fragment larger blocks.
What is an address space?
-A set of contiguous addresses that map to something else. i.e. hardware resources or other address spaces.
Physical address space
Actual addresses in RAM
Virtual/Logical Addresses
-Addresses seen by application.
-CPU provides hardware to map virtual addresses to physical addresses
Limit Register?
...
What are the Pros and Cons of the Base + Limit method?
Pros:
-Relocation is possible.
More efficient use of available RAM than without.

Cons:
-time consuming to grow a process's allocation (ie must relocate processes to make room)
-when a process is running, all of its memory must be present
What is Paged Memory?
-Decrease alocation overhead by using base + limit idea on very small memory "pages".

-Use fixed size pages to avoid specifying limit for each page. (4k is a std size.)
Physical page
page frame
virtual page
page
Paged Memory Pros and Cons?
Pros:
-Process memory no longer contiguous in physical memory. (no need for relocation)
-Easy to allocate additional memory to processes incrementally

Cons:
-Representing the virtual to physical mapping
-performance
What is a page table?
basically "base registers" stored in a big file.
How do page tables address pages?
Split addresses into two parts: page number and offset.
What are the standard (most common) page table address size and page size?
32bit address
4k page size
What is a guard page?
Pages with no permission that surround other valid memory. Provides a method for debugging buffer overflows.