Auxiliary Memory in computer Architecture.pptx

Auxiliary Memory

1. 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

2. Magnetic Disks A magnetic disk is a type of memory constructed using a circular plate of metal or plastic coated with magnetized materials. Usually, both sides of the disks are used to carry out read/write operations. However, several disks may be stacked on one spindle with read/write head available on each surface. The following image shows the structural representation for a magnetic disk.

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4. A magnetic disk is a circular plate constructed of metal or plastic coated with magnetized material. Often both sides of the disk are used and several disks may be stacked on one spindle with read/write heads available on each surface. All disks rotate together at high speed and are not stopped or started from access purposes. Bits are stored in the magnetized surface in spots along concentric circles called tracks. The tracks are commonly divided into sections called sectors. In most systems, the minimum quantity of information which can be transferred is a sector

5. A disk system is addressed by address bits that specify the disk number, the disk surface, the sector number and the track within the sector. After the read/write heads are positioned in the specified track, the system has to wait until the rotating disk reaches the specified sector under the read/write head. 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.

6. 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. 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

7. Magnetic Disk Advantages Non-volatile, high storage capacity cost-effective, durable widely compatible. Disadvantages of magnetic storage Slower access speeds sensitivity to physical damage size and weight power consumption noise.

8. Probably the cheapest form of storage per megabyte of storage Serial access so can be quite slow to access data Can store large amounts of data - up to 1 Terabyte per tape cartridge Need a special piece of equipment to record and read the data on the tape Can be set up to do the back up overnight or over the weekend The data may be corrupted if the tape is placed near a strong magnetic field e.g. a large speaker or magnet