This chapter presents the following content: Cache organization, locality of reference, two level model, suggested reading: stallings chapter 4. | Chapter 04 Computer Organization and Architecture CACHE MEMORY 1 KEY POINTS Computer memory is organized into a hierarchy. At the highest level (closest to the processor) are the processor registers. Next comes one or more levels of cache. When multiple levels are used, they are denoted L1, L2, and so on. The hierarchy continues with external memory, with the next level typically being a fixed hard disk, and one or more levels below that consisting of removable media such as optical disks and tape. As one goes down the memory hierarchy, one finds decreasing cost/bit, increasing capacity, and slower access time. If the cache is designed properly, then most of the time the processor will request memory words that are already in the cache. CACHE MEMORY . Computer Memory System Overview . Characteristics of Memory Systems Figure . Key Characteristics of Computer Memory Systems . Characteristics of Memory Systems An obvious characteristic of memory is its capacity. For . | Chapter 04 Computer Organization and Architecture CACHE MEMORY 1 KEY POINTS Computer memory is organized into a hierarchy. At the highest level (closest to the processor) are the processor registers. Next comes one or more levels of cache. When multiple levels are used, they are denoted L1, L2, and so on. The hierarchy continues with external memory, with the next level typically being a fixed hard disk, and one or more levels below that consisting of removable media such as optical disks and tape. As one goes down the memory hierarchy, one finds decreasing cost/bit, increasing capacity, and slower access time. If the cache is designed properly, then most of the time the processor will request memory words that are already in the cache. CACHE MEMORY . Computer Memory System Overview . Characteristics of Memory Systems Figure . Key Characteristics of Computer Memory Systems . Characteristics of Memory Systems An obvious characteristic of memory is its capacity. For internal memory, this is typically expressed in terms of bytes (1 byte 8 bits) or words. Common word lengths are 8, 16, and 32 bits. External memory capacity is typically expressed in terms of bytes. A related concept is the unit of transfer. For internal memory, the unit of transfer is equal to the number of electrical lines into and out of the memory module. . Characteristics of Memory Systems The unit of transfer may be equal to the word length, but is often larger, such as 64, 128, or 256 bits. Consider three related concepts for internal memory: Word: The “natural” unit of organization of memory. The size of the word is typically equal to the number of bits used to represent an integer and to the instruction length. Addressable units: In some systems, the addressable unit is the word. However, many systems allow addressing at the byte level. In any case, the relationship between the length in bits A of an address and the number N of addressable units is 2A= N. . .
