computer Memory Organization and Types of memory

computer organisation

1. Memory Organization Unit V

2. Contents Memory Hierarchy Main Memory Auxiliary Memory Associative Memory Cache Memory Virtual Memory Memory Management Hardware

3. Introduction Memory in a computer system can be divided into two main classes: main store and secondary store. Main store is the high speed memory used to hold the programs and data currently in use. Secondary store is the memory used for long term storage of data, e.g. a disk drive.

4. Memory Hierarchy The memory unit is an essential component in any digital computer since it is needed for storing programs and data Not all accumulated information is needed by the CPU at the same time Therefore, it is more economical to use low-cost storage devices to serve as a backup for storing the information that is not currently used by CPU

5. Memory Hierarchy The memory unit that directly communicate with CPU is called the main memory Devices that provide backup storage are called auxiliary memory The memory hierarchy system consists of all storage devices employed in a computer system from the slow by high-capacity auxiliary memory to a relatively faster main memory, to an even smaller and faster cache memory

6. Memory Hierarchy The main memory occupies a central position by being able to communicate directly with the CPU and with auxiliary memory devices through an I/O processor A special very-high-speed memory called cache is used to increase the speed of processing by making current programs and data available to the CPU at a rapid rate Magnetic tapes Magnetic disks I/O processor CPU Main memory Cache memory

7. Memory Hierarchy CPU logic is usually faster than main memory access time, with the result that processing speed is limited primarily by the speed of main memory The cache is used for storing segments of programs currently being executed in the CPU and temporary data frequently needed in the present calculations

8. Memory Hierarchy Register Cache Main Memory Magnetic Disk Magnetic Tape Cost, Speed Size, Storage Capacity

9. Multiprogramming The ability of the CPU to process a number of independent programs concurrently is called multiprogramming. Memory management system is the part of the operating system manages ,memory between different programs under use.

10. AUXILIARY MEMORY An Auxiliary memory is known as the lowest-cost, highest-capacity and slowest-access storage in a computer system. It is where programs and data are kept for long-term storage or when not in immediate use. The most common examples of auxiliary memories are magnetic tapes and magnetic disks . They are two types Magnetic Disks Magnetic Tapes

11. Magnetic Disks A magnetic disk is a type of memory constructed using a circular plate of metal or plastic coated with magnetized materials. Bits are stored in the magnetized surface in spots along concentric circles called tracks. The tracks are commonly divided into sections called sectors. Information transfer is very fast once the beginning of a sector has been reached. Disks may have multiple heads and simultaneous transfer of bits from several tracks at the same time. Disks that are permanently attached to the unit assembly and cannot be removed by the occasional user are called hard disks. A disk drive with removable disks is called a floppy disk.

12. Magnetic Tape The Magnetic tape itself is a strip of plastic coated with a magnetic recording medium. Bits are recorded as magnetic spots on the tape along several tracks. Usually, seven or nine bits are recorded simultaneously to form a character together with a parity bit. Read/write heads are mounted one in each track so that data can be recorded and read as a sequence of characters. Sequential access memory used for storing, backup, audio, video data etc . Highly reliable memory. Slower for read write operation. Magnetic tape units can be stopped, started to move forward or in reverse, or can be rewound. Gaps of unrecorded tape are inserted between records where the tape can be stopped