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A CPU cache is small because it needs to be extremely fast to access, which means it is physically located very close to the processor core, making it more expensive to manufacture and limiting its size compared to regular RAM; essentially, prioritizing speed over capacity is the key reason for its small size.

Key points about CPU cache:
Speed vs. Size:
The primary function of cache is to provide extremely quick access to frequently used data, so it prioritizes speed over storage capacity.

Physical proximity:
To achieve high speed, the cache needs to be physically close to the CPU core, which limits how much space can be dedicated to it.

Cost factor:
Building a large cache is expensive as it requires more complex circuitry and takes up more space on the chip.

Cache hierarchy:
To address the size limitations, most CPUs have multiple levels of cache (L1, L2, L3) with varying sizes and speeds, where L1 is the smallest and fastest, accessed most frequently