The Memory System

The Memory System - Memory Its all about storing...

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Memory It’s all about storing bits--binary digits Vacuum tubes, CRTs, drums, disks, core, ICs Issues of size, cost, speed Semiconductor memories (chips)
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Memory How to store How to organize--so as to be able to “store” a bit (or byte or word) and then find it again How to associate an address with a “set” of bits
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Up to 2 k addressable locations MDR MAR Figure 5.1. Connection of the memory to the processor. k -bit address bus n - bit data bus Control lines ( , MFC, etc.) Processor Memory Word length = n bits W R/
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Memory Memory access (read) address MAR MAR bus memory READ bus memory bus data processor bus MFC MDR bus
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Memory Memory access time: Time from Read issued to MFC received Memory cycle time: Time between two successive reads
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Memory Obviously, the speed of the processor depends on the speed of the memory Random Access Memory (RAM) simply means that access time is fixed (and the same) for all memory locations (addresses)
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FF Figure 5.2. Organization of bit cells in a memory chip. circuit Sense / Write Address decoder FF CS cells Memory circuit Sense / Write Sense / Write circuit Data input/output lines: A 0 A 1 A 2 A 3 W 0 W 1 W 15 b 7 b 1 b 0 W R / b ¢ 7 b ¢ 1 b ¢ 0 b 7 b 1 b 0 small (very) example (128 bit chip) 16 words of 8 bits each (16 x 8)
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Address decoder A 0 A 1 A 2 A 3 W 0 W 1 W 15 four input, sixteen output decoder 4 address lines, 16 word addresses word lines
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The Memory System - Memory Its all about storing...

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