Chapter 6 - Memory Hierarchy Flashcards
the locality principle stating that if a data location is referenced then it will tend to be referenced again soon
Temporal locality
the locality principle stating that if a data location is referenced, data locations with nearby addresses will tend to be referenced soon
Spatial locality
a structure that uses multiple levels of memories, as the distance from the processor increases, the size of the memories and the access time both increase
Memory hierarchy
the minimum unit of information that can be either present or not present in a cache
Block (or line):
the fraction of memory accesses found in a level of the memory hierarchy
Hit rate
the fraction of memory accesses not found in a level of the memory hierarchy
Miss rate
the time required to access a level of the memory hierarchy, including the time needed to determine whether the access is a hit or miss
Hit time
the time required to fetch a block into a level of the memory hierarchy from the lower level, including the time to access the block, transmit it from one level to the other, insert it in the level that experienced the miss, and then pass the block to the requestor
Miss penalty
one of thousands of concentric circles that make up the surface of a magnetic disk
Track
one of the segments that make up a track on a magnetic disk; the smallest amount of information that is read or written on a disk
Sector
the process of positioning a read/write head over the proper track on a disk
Seek
also called rotational delay. The time required for the desired sector of a disk to rotate under the read/write head; usually assumed to be half the rotation time
Rotational latency
a cache structure in which each memory location is mapped to exactly one location in the cache
Direct-mapped cache
a field in a table used for a memory hierarchy that contains the address information required to identify whether the associated block in the hierarchy corresponds to a requested word
Tag
a field in the tables of a memory hierarchy that indicates that the associated block in the hierarchy contains valid data.
Valid bit
a request for data from the cache that cannot be filled because the data are not in the cache
Cache miss
a scheme in which writes always update both the cache and the next lower level of the memory hierarchy, ensuring that data are always consistent between the two
Write through
a queue that holds data while the data are waiting to be written to memory
Write buffer
a scheme that handles writes by updating values only to the block in the cache, then writing the modified block to the lower level of the hierarchy when the block is replaced
Write-back
a scheme in which a level of the memory hierarchy is composed of two independent caches that operate in parallel with each other with one handling instructions
Split cache
a cache structure in which a block can be placed in any location in the cache
Fully associative cache
a cache that has a fixed number of locations (at least two) where each block can be placed
Set-associate cache
a replacement scheme in which the block replaced is the one that has been unused for the longest time
Least recently used (LRU)
a memory hierarchy with multiple levels of caches, rather than just a cache and main memory
Multilevel cache
the fraction of references that miss in all levels of a multilevel cache
Global miss rate
the fraction of references to one level of a cache that miss, used in multilevel hierarchies
Local miss rate
A code that enables the detection of an error in data, but not the precise location and, hence, correction of the error.
Error detection code
a technique that uses memory as a “cache” for secondary storage
Virtual memory
an address in main memory
Physical address
a set of mechanisms for ensuring that multiple processes sharing the processor, memory, or I/O devices cannot interfere, intentionally or unintentionally, with one another by reading or writing each other’s data. The mechanisms also isolate the operating system from a user process.
Protection
an event that occurs when an accessed page is not present in main memory
Page fault
an address that corresponds to a location in virtual space and is translated by address mapping to a physical address when memory is accessed
Virtual address
