lyx_Ch04.pptVIP

William Stallings Computer Organization and Architecture6th Edition Chapter 4 ※Cache Memory（重点） §4.1 Computer Memory System Overview Location Capacity Unit of transfer Access method Performance Physical type Physical characteristics Organisation (1)Location CPU (registers, cache) Internal (main memory, cache) External (disk, tape) (2)Capacity Word size —word length (字长) The natural unit of organisation 8,16,32bits Number of words (字数) or Bytes 注意：字（word）在不同的机器上位数不同，它不是一个公认的单位，而字节是标准单位：1Byte=8bits (3)Unit of Transfer Internal – “word” Usually governed by data bus width Be equal to the word length (size) (or xx bits) External – “block” Usually a block which is much larger than a word(e.g.4,8,16…) “1block=2n words “ (4)Access Methods (1) Sequential access 顺序存取 Start at the beginning and read through in order Access time depends on location of data and previous location e.g. tape Direct access 直接存取 Individual blocks have unique address Access is by jumping to vicinity plus sequential search Access time depends on location of data and previous location e.g. disk Access Methods (2) Random access 随机存取 Individual addresses identify locations exactly Access time is independent of location or previous access e.g. RAM(Main memory) Associative access 关联存取 Data is located by a comparison with contents of a portion of the store Access time is independent of location or previous access e.g. cache (5)Performance Access time 存取时间 Time between presenting the address and getting the valid data Memory Cycle time存储周期 Time may be required for the memory to “recover” before next access Cycle time is access + recovery Transfer Rate 传输速度 Rate at which data can be moved Note: Access 存取，访问（忽略方向） =Fetch store（方向性） (6)Physical Types Semiconductor 半导体 RAM （DRAM SRAM) Magnetic 磁 Disk Tape Optical 光 CD DVD Magnetic – Optical 磁-光 MO(用的少) (7)Physical Characteristics Volatile/nonvolatile 易失性 非易失性 Erasable/nonerasable 可擦除 不可擦除 2.Memory Hierarchy