More about Cache

1. More about Cache Writing Data to the Cache Cache Performance Average Memory Access Time

2. Writing Data to the Cache When executing a program, some information may need to be written into memory using either write-through or write-back. Write-through: Every time a value is written from CPU into a location in cache, it is also written to the corresponding location in physical memory Guarantees that physical memory is correct Requires additional time to write to physical memory Write-back: The value written to cache is not always written to physical memory Saves time

3. Write-through + Write-back Example For I = 1 to 1000 x = x +1 With write-through every value of x will be written to memory While write-back only the final value will be saved into physical memory

4. Additional Stuff Since a processor cannot take data from another processor's cache, the physical memory should have the most current value Write miss: Write miss writes data to locations not currently loaded into the cache Write-allocate policy: Loads the location into cache then writes the new value to cache using write-back or write-through Write-no allocate policy: Updates the value in physical memory without loading it into the cache.

5. Additional Stuff Con't. Sooo write-back policy usually uses write-allocation While write-through policy usually uses write-no allocation.

6. Average Memory Access Time

7. Examples of Memory Access Time

8. More Examples

9. More Examples

10. More Examples

11. References