L5 - Memory Hierarchy Flashcards
Write Through
Update memory immediately. Short and simple execution but higher energy consumption due to higher number of writes.
Spatial Locality
Spatial Locality describes the concept that data which gets accessed frequently is arranged close together in the cache.
Direct Mapping
Each element has its particular cache line. DM is simple to implement but does not utilise cache resources efficiently due to frequent use of same high miss rate.
What does Temporal Locality describe?
Temporal Locality describes the concept that data which gets accessed likely and more often will get accessed soon.
Memory Hierarchy
high speed: Cache (SRAM) < Main Memory (DRAM) < Virtual Memory (SSD/HDD) : capacity
What does SDRAM stand for?
SDRAM or Synchronous Dynamic Random Access Memory provides large data storage at low cost and gets accessed when the cache misses. Data is stored in banks. PRO: large data storage at low cost and small area; advanced safety applications; fast CON: difficult for worst-case timing analysis
LRU
Least Recently Used. If all cache lines are valid; the one with that was least recently used (highest LRU) gets overwritten.
Fully Associative with Round Robin/FIFO
The initially empty cache gets filled in a Round Robin manner.
- PRO: simple and less chip are, a mimics LRU (better performance than direct mapped)
- CON: slightly more complicated to predict, slightly less performance than LRU
Fully Associative with LRU (Least Recently Used)
In the initially empty cache each memory address can be associated to any cache line.
- PRO: conflict misses are avoided, leads to a higher utilization and good performance for most of the applications.
- CON: most complex architecture, huge size (LRU) due to counters and comparators.
Set Associative Cache
Hybrid: fully associative + direct mapping. Cache lines are grouped in sets and data can be stored in any cache line within the set.
Define: Miss Penalty.
memory access time
Write Back
Write to cache and write to memory when replaced (dirty line). Less number of writes (energy efficient) and short execution time but difficult to implement (comparators needed).
