Lecture 6: The Walls to Sequential Computing. Moore’s Law.
- Wrap up Caches
- Virtual Memory
- Handling a write-hit
- Write-through
- Write-back
- Handling a write-miss
- Write-allocate
- No-write-allocate
- Typical combos in practice
- Write-back + Write-allocate (more common)
- Write-through + No-write-allocate
Miss rate is more important than the hit rate: 97% hit rate is ~2 times worse than 99% hit rate
Cache Capacity Effects from Memory Mountain
Why memory virtualization?
- Ease of use (running programs that require more memory than physically available)
- Isolation (running multiple programs simultaneously)
- Protection
- A page of virtual memory corresponds to a frame of physical memory
- Page table enables the translation of virtual address into physical addresses
- The page table is stored in main memory
- If the page table is accessed for each address translation, this would be very costly
- Translation Lookaside Buffer (TLB): "Cache" for the addr translation process
