Factor 3: Cache Memory (L1, L2, L3)

Factor 3: Cache Memory (L1, L2, L3)

What It Is:

Cache is a small amount of very fast memory built directly into the CPU chip. It stores frequently-used data and instructions so the CPU doesn't have to wait for slower RAM.

Cache Levels:

• L1 Cache: Smallest (32-128 KB per core), fastest, located closest to CPU cores. Separate for instructions and data.
• L2 Cache: Medium (256 KB - 1 MB per core), slightly slower than L1, still very fast.
• L3 Cache: Largest (4-64 MB shared across all cores), slowest cache level but still much faster than RAM.

How It Works:

• When CPU needs data, it checks L1 first (fastest)
• If not in L1, checks L2
• If not in L2, checks L3
• If not in any cache, fetches from RAM (slowest) - called a "cache miss"
• Cache hit rate: % of time data is found in cache (higher is better)

How It Affects Performance:

• More cache = fewer RAM accesses = faster performance
• Cache is 50-100x faster than RAM!
• Example: L1 cache access = ~4 clock cycles, RAM access = ~200 clock cycles
• Larger cache means more data can be kept close to CPU