Memory is part of the computer that serves as a repository of information that must be managed and maintained properly. Most computers have a memory hierarchy consisting of three levels, namely:
Register in the CPU, located at the top level. The information in the registers can be accessed in one CPU clock cycle.
Primary Memory (executable memory), located at the middle level. For example, RAM. Primary Memory is measured by one byte at a time, a relative can be accessed quickly, and is volatile (the information can be lost when the computer is turned off). CPU to access memory with a single load and store instructions within a few clock cycles.
Secondary Memory, located in lower level. For example, disk or tape. Secondary Memory is measured as a collection of bytes (block of bytes), slow access time, and is non-volatile (the information is retained when the computer is turned off). This memory is implemented in storage devices, so access to include action by the driver and the physical devices.
Computers that are more sophisticated level is more on the memory hierarchy system, namely cache memory and other forms of secondary memory, such as rotating magnetic memory, optical memory, and sequntially access memory. However, each level is only an improvement of one of three basic levels that have been described previously.
Part of the operating system that regulates memory hierarchy is called the memory manager. In this era of multiprogramming, memory manager is used to prevent the process of writing and reading by other processes that are located in primary memory, set the swapping between main memory and disk when main memory is too small to hold all processes.