Question

Cache replacement algorithms

(a) What is a victim block?
(b) Three caching schemes have been taught. Which caching scheme does not need a victim block selection algorithm?
(c) What are the three most used cache replacement algorithms/policies?
(d) Effective memory access time

a) (a) Data block replaced in cache
(b) LRU
(c) FIFO, LRU, Random
(d) Time taken to access cache memory
b) (a) Data block replaced in cache
(b) FIFO
(c) LRU, FIFO, Random
(d) Time taken to access main memory
c) (a) Cache block replaced by victim block
(b) Random
(c) LRU, FIFO, MRU
(d) Time taken to access RAM
d) (a) Cache block replaced by victim block
(b) FIFO
(c) LRU, FIFO, Random
(d) Time taken to access cache memory

Answer 1

Victim blocks are cache blocks replaced by new data, and direct-mapped caches don't need a victim block selection algorithm. The three most common cache replacement algorithms are LRU, FIFO, and Random. Effective memory access time is the average time taken for data retrieval from cache and main memory.

Step-by-step explanation:

Cache replacement algorithms are crucial for managing the data that is stored in a computer's cache. When the cache is full, and a new data block needs to be loaded, a decision has to be made about which existing block to replace. This is where the concept of a victim block comes into play. A victim block is a cache block that is selected for replacement by the new incoming block.

There are various cache replacement policies, but among them, a direct-mapped cache alignment does not require a victim block selection algorithm because each block has a predetermined cache line where it can be placed. If a new block needs to be placed in the cache, it simply replaces the block that is currently in its designated cache line.

The three most common cache replacement algorithms are:

1. Least Recently Used (LRU): Replaces the block that has not been used for the longest time.
2. First-In, First-Out (FIFO): Replaces blocks in the order they were loaded into cache.
3. Random: Randomly selects a block to replace.

Effective memory access time refers to the average time it takes to access memory, which includes the time to access data from the cache and the possible time to retrieve data from the main memory in case of a cache miss.