The working memory of a computer, also called main memory, is a volatile read/write memory that is available to the central processing unit( CPU) for fast access to data. The main memory is a random access memory( RAM) that is directly connected to the central processing unit via the memory bus. Correctly, it should be noted that there is also a cache in between.
The main memory is the primary memory. It is used by the central processing unit (CPU) for direct access to data and commands. The memory capacity of the main memory, in conjunction with the CPU power, is decisive for the computer's performance. The main memory has a limited address range, which is defined by the address bus width of the central processing unit. Working memories are byte-oriented, which means that data is transported to and from the working memory byte by byte or in multiples of a byte, e.g. 16 bits or 32 bits in parallel.
In the DOS operating system the addressing area is divided into several subareas, and consists of the conventional memory and the extended memory, the Extended Memory Specification( XMS). Only by this extended memory 32 megabyte( MB) addressing area are realizable.
The memory cells of the main memory can be addressed directly and are characterized by a short access time, which can be increased considerably by increasing the clock rate as with Single Data Rate( SDR), Double Date Rate( DDR) or Quad Data Rate ( QDR). Depending on the memory technology used - Random Access Memory (RAM), Dynamic RAM( DRAM), Static RAM ( SRAM), Synchronous Dynamic RAM( SDRAM), Rambus DRAM ( RDRAM), Direct Rambus DRAM( DRDRAM), Double Date Rate Synchronous DRAM ( DDR-SDRAM), Video RAM( VRAM) - the access times are in the single- digit nanosecond range.