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Chapter 8 : Memory Introduction

Computer Second Component : Fundamentals of Memory

7 April, 2018     

Memory organizes in the form of cell each cell is able to identified with a unique no called as ADDRESS.  Each cell is able to recognize two control signals read & write. 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. Next comes main memory, which is usually made out of dynamic random-access memory (DRAM).

All of these are considered internal to the computer system. 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. It would be nice to use only the fastest memory, but because that is the most expensive memory,

we trade off access time for cost by using more of the slower memory. The design challenge is to organize the data and programs in memory so that the accessed memory words are usually in the faster memory. In general, it is likely that most future accesses to main memory by the
processor will be to locations recently accessed. So the cache automatically retains a copy of some of the recently used words from the DRAM. If the cache is designed properly, then most of the time the processor will request memory words that are already in the cache.

Different pins supported by the Processor:

  1. Active Low Pins : These pins are enabled when i/p is zero like RD,WR.
  2. Active High pin: These pins is enabled when the i/p is One.
  3. Time multiplexed Pin: These pin carries the multiple functionalities but the meaning is defined by another pin.  Like When ALE = 1 it act like a Address line but ALE = 0 then it act like a Data Line.
  4. UNI pin: This pin contains only one meaning. This pin may be a Active Low Pin or Active High Pin.
  5. Dual Pin: Multiple Meanings means single pin carries two things.
  6. Input Pin: It carries some information towards Processor.
  7. Output Pin : Information towards external components.

Components of Computer System:

  • CPU                 :   Processing of Program
  • Memory          :   Storage of Program
  • Input/Output  :   Provide External Communication

Having 3 components is not the criteria but how well three components are interconnected to each other to satisfied the goal of the system is the Criteria. 

The communication channel used in the computer is called as BUS. Characteristics of Bus is shared transmission media. The Limitation of Bus is only one transmission at a Time.

Next We will study Bus Configuration and Interconnection.

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