메모리 계층 구조

■ principle of locality
- temporal locality … the tendency to re-use recently accessed data items
[ex] loops
- spatial locality … the tendency to reference data items that are close to other recently
accessed items [ex] sequential execution, array or data accesses
■ memory hierarchy
- exploiting the principle of locality
- multiple levels of memory with different speeds and sizes

memory technology
typical access time
$ per Mbyte in 1993
SRAM
8 ～ 35 ns
$100 ～ $400
DRAM
90 ～ 120 ns
$25 ～ $50
magnetic disk
10,000,000 ～ 20,000,000 ns
$1 ～ $2

- faster memory … close to the processor
slower and less expensive memory … below that
■ 2-level model for simplicity
- upper level … smaller, faster, more expensive
lower level … larger, slower, less expensive
- block … minimum unit of information transfer between the two levels (see Figure 7.2)
- hit … when the data requested by the processor appears in some block in the upper level
miss … when the d…