Memory Management Flashcards
What are the 5 problems with managing memory?
- Protection
- Relocation
- Room for Growth
- Fragmentation
- Allocation
Protection Includes:
Accidental/Intentional Clobbering
- write memory from another job
- read value from uncontrolled memory
Resolutions
- correct relocation
- protection words (IBM/360)
- base/limit registers (CDC 6600, intel 8080)
Contiguously Allocated
process is stored in a single block of memory.
Relocation Includes:
Memory Location
- process memory start is not static
- memory start is not predictable
Resolutions
- make and change all jumps during loading
- linker must ID all jumps
Room for Growth includes:
Allocate growth space
- stack for calls
- heap for dynamic variables
Swap what is used
- if we haven’t used space, don’t save it.
Fragmentation Includes:
External
- wasted space is not contiguous
- total space exists to satisfy a request
Internal
- wasted space inside allocated partition.
-allocated memory may be slightly larger than requested memory.
Allocation includes:
Bitmapped Memory
- Table of memory “Chunks”
* 1 = occupied
0 = unused
- Size of chunk
* Large chunk = small map,
low utilization
* Small chunk = large map,
high utilization
- Searching map is slow
List Memory
- Allocation (algorithms for
fining free space)
* First fit
* Best fit
What is paging?
Paging breaks the virtual address space into fixed sized pieces and physical address space into pieces of the same size.
What is the difference between pages and frames.
Pages break into virtual memory while frames break into physical memory.
Attempting to access a page that is not stored in physical memory is called a __________ .
Page Fault
A ________ is a small, fast memory that speeds up memory access time.
Cache
What states that if we have accessed a memory location before, we are likely to access it again soon.
Locality
