note9 - CSCI 120 Introduction to Computation CPU speed...

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Unformatted text preview: CSCI 120 Introduction to Computation CPU speed (draft) Saad Mneimneh Visiting Professor Hunter College of CUNY 1 Introduction We will look at three main factors in determining the speed of the processor: Cache memory, pipelining, and the clock speed. 2 Cache memory Let us now look at all kinds of memory that we have seen so far. We have: main memory (short term memory): this is used to hold data that will be needed by the program in the near future mass storage devices such as hard disks (long term memory): these are used to hold data that is unlikely to be needed in the near future, but that will eventually be needed at some point in time registers (very short term memory): these are used to hold the data im- mediately applicable to the current instruction being executed or to the operation at hand. Figure 1 shows all three levels of memories with their placement relative to the CPU. CPU storage device e.g. Hard Disk main memory registers closer to CPU, faster, smaller, shorter, more expensive Figure 1: Memory levels Most computers have an additional memory level called cache memory 1 . Cache memory is a high speed memory (but more expensive than RAM) located within the CPU itself (one may view it as being between main memory and the registers). It is usually few hundreds of KB. The computer attempts to keep a copy of the portion of main memory that is of current interest in the cache. Therefore, data transfers that would normally be made between registers and main memory are made between registers and cache memory. Any changes made to the cache are transferred collectively to main memory at a more opportune time. The result is that the CPU can execute instructions more rapidly because it is not delayed by the communication with main memory. This statement,it is not delayed by the communication with main memory....
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This note was uploaded on 03/27/2010 for the course CSCI 120 taught by Professor Saadmneimneh during the Spring '09 term at CUNY Hunter.

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note9 - CSCI 120 Introduction to Computation CPU speed...

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