Subject: Computer Organization

Topic: Memory Organization

Difficulty: Medium

Various characteristics of memory are : -

• Location - This characteristic represents whether the location is external or internal to the computer. External memory is the seperate storage device such as disk and tape. It is accessed by the processor through I/O controllers. Internal memory is mostly embedded within the computer. It is in various forms such as registers, cache and main memory.

• Capacity - It is the most important characteristic of the memory system. It is different for external and internal memory. Capacity of the external memory is measured in terms of bytes. Whereas the capacity of internal memory is measured in terms of bytes or words, wherein word length may be 8, 16 or 32 bits.

• Direct Access Method - In this method every block has its own unique address. Here, the access is made directly by first reaching to vicinity and then following sequential search. Access time of this method is concerned with current and previous location of data. An example of this method is hard disk.

• Sequential Access Method - In this method access to data is made sequentially. Like direct access method, it also makes use of shared read-write mechanism. Tape is an example of this method. Access time is different with that of direct access but depends on same parameters.

• Random Access Method - In this method each block of memory has its unique and physically wired-in addressing mechanism. Unlike direct and sequential access, the access time of this method doesnot depend on location . RAM is an example of this method.

• Associative Access Method - In this method unlike other methods, access to data is made by comparing the required bit location within a word based on the specified data element. Therefore the access time of this method also depend on location. Cache memory is the example of this method.