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23 Cards in this Set
- Front
- Back
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What are the two main users of memory?
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- OS
- Applications |
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What are two ways to track memory usage?
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-Linked lists
-Bitmaps |
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What is a "Free List"?
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A linked list being used for memory management.
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How does a bitmap keep track of memory allocation?
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- One bit per chunk.
- 1 = chunk in use - 0 = chunk free |
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What is contigous memory management?
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-Memory is allowcated in a contigous piece. memory for low level device i/o.
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What is noncontigous memory management?
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Memory not necissarily allocated in one piece.
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How efficient is Contiguous memory allocation?
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Since blocks may not be used up there can be small fragments left over. 110 byte allocation. 128 byte block. 18 bytes left over.
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Explain best fit algorithm.
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Small as possible chunk allocated.
Pros: Leaves larger blocks for future requests. Cons Leaves runt blocks. |
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Explain Worst Fit Algorithm.
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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. |
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Explain first fit algorithm.
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-Use the first block that is large enough to fill the request.
Pros: -Fast search speed. Cons: -May unnecessarily fragment larger blocks. |
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What is an address space?
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-A set of contiguous addresses that map to something else. i.e. hardware resources or other address spaces.
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Physical address space
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Actual addresses in RAM
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Virtual/Logical Addresses
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-Addresses seen by application.
-CPU provides hardware to map virtual addresses to physical addresses |
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Limit Register?
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...
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What are the Pros and Cons of the Base + Limit method?
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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 |
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What is Paged Memory?
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-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.) |
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Physical page
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page frame
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virtual page
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page
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Paged Memory Pros and Cons?
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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 |
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What is a page table?
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basically "base registers" stored in a big file.
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How do page tables address pages?
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Split addresses into two parts: page number and offset.
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What are the standard (most common) page table address size and page size?
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32bit address
4k page size |
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What is a guard page?
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Pages with no permission that surround other valid memory. Provides a method for debugging buffer overflows.
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