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Storage Device

The Eight(8) Characteristics of Memory Systems are as highlighted below:

1. Location: This shows whether the location of the memory device is external or internal to the computer. Internal memory and external memory are a lot different from each other. While the internal memory is embedded directly on the computer motherboard, external memory is separate from the main computer unit, in the form of a storage disk such as disks and tapes. External memory devices are controlled from the I/O controllers, while internal memory takes the form of cache memory, registers and main memory.

2. Capacity: Capacity is a measure of amount of data the memory device can store. For internal memory, this is measured in terms of bytes, while in external memory, it is measured in bytes or words, where a word length may be 8,16 or 32 bits.

3. Access Method: Access methods refers to the methods through which data is written to, and consequently read from a memory device. There are four access methods which are as listed below;

  • Direct Access Method
  • Sequential Access Method
  • Random Access Method
  • Associative Access Method

Direct Access Method: Every memory block is marked by a unique address. Access is made directly by first reaching to the vicinity and the following  sequential search. An example of a memory device that uses the direct access method is the hard disk.

Sequential Access Method: Uses a shared read-write mechanism to sequentially access data. An example of a storage device that uses the sequential access method is the tape.

Random Access Method: Each block in memory has its unique and physically wired-in addressing mechanism. An example of a storage device that uses the random access method is the RAM.

Associative Access Method: Access to data is made by comparing the required bit location within  a word based on a specified data element. An example of a storage device that uses the associative access method is the cache memory.

4. Unit of Transfer: This is a measure of the transfer rate of the data in and out of memory. In internal memory, this is determined by the number of electrical lines going into and coming out of the memory with each line carrying data of word length. In external memory, this is determined by the number of bits read out or written into the memory at a time.

5. Performance: This a measure of overall efficiency of the memory system. There are three(3) parameters used to measure performance.

  • Transfer Rate
  • Memory Cycle Time
  • Access Time

Transfer Rate: This is the rate at which data is transmitted into and out of memory.

Memory Cycle Time: The time required to access a block in memory as well as the period to the start of the second access.

Access Time: The time required to carry-out read or write operation.

6. Physical Type: This is the shape and form the memory takes. There are about four(4) of such forms which are as listed below:

  • Magnetic
  • Semiconductor
  • Optical
  • Magneto-optical

7. Organization: The organization of a memory system generally refers to the physical arrangement of the bits.

8. Physical Characteristics: This is the nature of the memory system. This can take the forms listed below;

  • Volatile
  • Non-volatile
  • Erasable
  • Non-erasable

Please leave a comment below if you found this explanation helpful. Happy learning!

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