Function Of Main Memory

Main memory

o                                    Main memory is an integral part of computer. Main memory is volatile unlike from magnetic tape and disks storage. Volatile means that the data is lost when the system is shut off. Main memory provides a direct access to the stored data similar to the disks storage. The main memory is small in size as compared to other storage devices. The main memory not only store data it has been save application program and system program, but actually the database is not fit in main memory. 

o      The main memory has a portion it is called a buffer. The data that is processed must be brought into the buffer. The buffer contains a copy of the records but actually the records still exists on the disks. The process of accessing records is many time faster in the buffer as compared to the records accessing on the disk. The system must checks the requested record if it is already in the buffer or not. If the buffer have a requested records then simply passes the address in the buffer to the requesting process. If the requested record is not in the buffer then the location of the record on the disks is find and directs the reading of the record into the buffer. The most frequently used data are sometime kept in the buffer whenever the database is in use. The main memory reads more than one record at a time.  

      Cache memory

o                           The small portion of a main memory with very high speed memory chips is called a cache memory. Dynamic random access memory chips are used in main memory mostly. Before reading a data in Dynamic random access memory it always required to be refreshed or regenerated. Static random access memory chip are also used in small portion of the memory. Static random access memory is more expansive and it is faster than random access memory and does not need to be refreshed or regenerated before reading a data. The access time of dynamic random access memory is an 80 to 120 nanosecond, and static random access memory has a 25 to 35 nanosecond. The simple question arises in the mind why cache memory is used???? What is the purpose of cache memory???? A cache memory provides a quick access for this reason processor does not wait for the data which is requested. The system must ensure that data always in cache when required. Cache controllers use statistical procedure to decide which data is kept in cache.