Memory Units And Memory Hierarchy Computer Science

Memory organisation is combination of several memory devices efficiently. Memory devices are combined and organised based on their characteristic such as access time, speed, storage capacity, physical size and cost per byte. Memory devices organised in such a way that computer system should operate at highest speed, provide bulky storage capacity, smaller in size and less in a cost. Memory organisation uses primary memory devices and secondary memory devices.

3.2 Memory Unit

Memory unit is storage unit of the computer system. It stores content such as instructions (codes) and data for temporary or permanent purpose. It is used to stores content and to retrieves the content when needed by CPU or user. Memory unit includes two types of memory: primary (main) and secondary. Instruction or data given by input devices is first getting stored in the primary memory. Further users saves processed (executed) data in the secondary memory. Primary memory is volatile (temporary). It is faster than secondary memory. It includes RAM and ROM. It is directly accessible by CPU. Secondary memory is non-volatile (permanent). It includes several secondary storage devices such as Hard Disk Drive (HDD), Floppy Disk Drive (FDD), CDROM, and DVD and so on. Figure 3.1 shows memory unit and communication line with other units.

Note: Volatile memory loses its content when computer loses power. In non-volatile memory power loss of computer does not affects content.

Input UnitProcess UnitOutput UnitPrimary MemorySecondary MemoryMemory Unit

Figure 3.1 memory unit and communication lines with I/O unit and Process unit

3.3