Computer Memory Hierarchy free essay sample

Write policies on write hit are as follows: Write Through: the information is written to both the block in the cache and to the block in the lower-level memory. Advantages of Write Through are read miss never results in writes to main memory and main memory always has the most current copy of the data (consistent). Disadvantages of Write Through are write is slower and every write needs a main memory access (uses more memory bandwidth). Write Back: the information is written only to the block in the cache. The modified cache block is written to main memory only when it is replaced. To reduce the frequency of writing back blocks on replacement, a dirty bit is commonly used. This status bit indicates whether the block is dirty (modified while in the cache) or clean (not modified). If it is clean the block is not written on a miss. Advantages of Write Back are writes occur at the speed of the cache memory, and multiple writes within a block require only one write to main memory (uses less memory bandwidth). We will write a custom essay sample on Computer Memory Hierarchy or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page Disadvantages of Write Back are main memory is not always consistent with cache, and harder to implement. Two write miss policies: Write Allocate the block is loaded on a write miss, followed by the write-hit action. No Write Allocate the block is modified in the main memory and not loaded into the cache. Although either write-miss policy can be used with write through or write back, write back caches often use write allocate and write through caches often use no write allocate. Source: 1. Computer Architecture