Importance of Cache Memory (2 Marks)

Cache is a small, very fast SRAM between CPU and main memory that bridges the speed gap between high-speed processor and relatively slow DRAM main memory.

1. Speed Gap: CPU cycle time is ~1ns while DRAM access is ~50-100ns. Without cache, CPU would stall waiting for memory. Cache (access ~2-5ns) supplies most needed words at CPU speed.
2. Exploits Locality of Reference: Due to temporal locality (recently used data reused soon) and spatial locality (next addresses likely accessed), ~90-95% accesses hit in cache, giving average access time ≈ cache time.
3. Result: Improves effective memory access time, increases throughput, reduces memory bandwidth demand. Hence hit ratio and system performance increase significantly despite small size and high cost/bit.