MemoryHieraaechy - 1.1 Memory Hierarchy Memories are...

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1.1 Memory Hierarchy Memories are characterized by their function, capacity, and response times. Operations on memories are called reads and writes , defined from the perspective of a processor or other device that uses a memory: a ‘ read’ transfers information from the memory to the other device, and a ‘ write ’ transfers information into the memory. There are many types of storage devices are used in a computer system such as: Registers: These are temporary storage device where data can store just before or /and after some operations (such as arithmetic or logical). There are few number of registers in a processor and each register can hold only one word of data ( 1 byte, 2 bytes etc). Cache memory: This type of memory presents in processor chip. The main function of cache memory is to increase the memory access time. Main memory: There are two types of main memory present in a system – RAM (Random access memory) and ROM (Read only memory). RAM is a volatile memory. If the power off, the contain of RAM is totally erased. User can store or/ and remove data to the RAM. In ROM user cannot write any thing, just read its contain only. Generally booting procedure, micro programs are written in ROM. Figure1.1: Memory hierarchy model Secondary memory: It is often implemented by a disk or tape where we can store data permanently. The size of the secondary memory is larger than the all types of memories. Now, we can represent a memory hierarchy diagram below according to their size and the access time. The effectiveness of a memory hierarchy depends on the principle of moving information into the fast memory infrequently and accessing it many times before replacing it with new information. The memory hierarchy can be characterized by a number of parameters. Among these parameters are the access time, capacity, cost per byte, cycle time, unit of transfer, latency, bandwidth and cost.
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Access time: Access time, also known as response time or latency , refers to how quickly the memory can respond to a read or write request. The access time t i refers that the time between request to i-th level of memory and word arrives from that level of memory to the processor. Cycle time: The cycle time is defined as the time elapsed from the start of a read operation to the start of a subsequent read. Latency: The latency is defined as the time interval between the request for information and the access to the first bit of that information. Bandwidth: The bandwidth provides a measure of the number of bits per second that can be accessed. The bandwidth b i refers to the rate at which information is transferred from i-th level to its adjacent levels. Cost per byte: The cost of a memory level is usually specified as price per bytes and it is denoted by c i , i.e. cost per byte at i-th level of memory. Capacity:
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This note was uploaded on 10/16/2011 for the course CSE 106 taught by Professor Fgh during the Spring '11 term at Burlington CC.

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MemoryHieraaechy - 1.1 Memory Hierarchy Memories are...

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