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.

4. RULES

5. • 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

6. • 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.

7. • 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

9. • 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.

10. 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