3. Storage devices and media
Magnetic media and magnetic storage devices
Magnetic tape drives
A magnetic tape is a very thin strip of plastic which is coated in a magnetic layer. They are
read from or written to by a read/write head in a magnetic tape storage device. The data is
stored as a magnetized area (which represents a 1) or demagnetized area (which represents a
0) and is read from the tape using serial access.
Uses of magnetic tape
1. Use in applications where batch processing is used (for example, clearing bank cheques,
utility billing ).
2. Used as a backup media where vast amounts of data need to be stored.
3. Used in long-term archiving of data; magnetic tapes have huge data storage capacities
and are known to be very stable, which makes them ideal for long-term storage.
Advantages of magnetic tapes Disadvantages of magnetic tape
They are generally less expensive (per Very slow data access times because
byte) than the equivalent hard disk they use serial access,
drive.
The process of updating data using
It is a very robust technology and o not magnetic tapes using a master tape (the
deteriorate overtime original) and a transaction tape
(containing changes) to create a new
They have a huge data storage capacity.
master tape is a slow and can also
The data transfer rate is actually fast introduce errors
a strong magnet can corrupt data stored
on the tape.
Hard disk drives (HDD)
in a Hard disk drives (HDD) Data is stored in a digital format on the magnetic surfaces of the
hard disks (or platters).
3. Storage devices and media 1
, how HDD works:
1. voice coil Actuators are used to move the read/write heads
2. A read/write arm swings the read/write head back and forth across the platter(made from
glass, ceramic or aluminum and coated in iron oxide.); that is rotating at up to 10000 rpm
(revolutions per minute).
3. Each read/write head contains a tiny magnet which allows the data on the platter to be
read.
4. There are two read/write heads per platter (one for the top surface and one for the bottom
surface).
5. Data is stored in concentric, circular tracks; each track is broken up into sectors.
6. A map of the sectors is stored on the HDD and is known as a file allocation table (FAT);
when the computer wants to store new data, it looks at the FAT map to find out which
sectors are free and then moves the read/write heads to the correct location
Uses of fixed hard disk drives
1. To store the operating system, systems software and working data/files.
2. Storing applications software.
3. Used in real-time systems (for example control of a chemical plant) and in online
systems (for example, booking airline tickets).
4. Used in file servers for computer networks.
Advantages of fixed hard disk drives Disadvantages of fixed hard disk drives
They have a very fast data transfer rate They can be fairly easily damaged (for
and fast access times to data. example, if shut down incorrectly
They have very large memory They have many moving parts which
capacities. can affect their overall reliability.
Their read/write operation can be noisy
when compared to solid-state drives.
Portable hard disk drives
A portable hard disk drive (HDD) is an external storage device that is designed to be easily
portable and used with multiple computers or devices.
Uses of portable hard disk drives
3. Storage devices and media 2
Magnetic media and magnetic storage devices
Magnetic tape drives
A magnetic tape is a very thin strip of plastic which is coated in a magnetic layer. They are
read from or written to by a read/write head in a magnetic tape storage device. The data is
stored as a magnetized area (which represents a 1) or demagnetized area (which represents a
0) and is read from the tape using serial access.
Uses of magnetic tape
1. Use in applications where batch processing is used (for example, clearing bank cheques,
utility billing ).
2. Used as a backup media where vast amounts of data need to be stored.
3. Used in long-term archiving of data; magnetic tapes have huge data storage capacities
and are known to be very stable, which makes them ideal for long-term storage.
Advantages of magnetic tapes Disadvantages of magnetic tape
They are generally less expensive (per Very slow data access times because
byte) than the equivalent hard disk they use serial access,
drive.
The process of updating data using
It is a very robust technology and o not magnetic tapes using a master tape (the
deteriorate overtime original) and a transaction tape
(containing changes) to create a new
They have a huge data storage capacity.
master tape is a slow and can also
The data transfer rate is actually fast introduce errors
a strong magnet can corrupt data stored
on the tape.
Hard disk drives (HDD)
in a Hard disk drives (HDD) Data is stored in a digital format on the magnetic surfaces of the
hard disks (or platters).
3. Storage devices and media 1
, how HDD works:
1. voice coil Actuators are used to move the read/write heads
2. A read/write arm swings the read/write head back and forth across the platter(made from
glass, ceramic or aluminum and coated in iron oxide.); that is rotating at up to 10000 rpm
(revolutions per minute).
3. Each read/write head contains a tiny magnet which allows the data on the platter to be
read.
4. There are two read/write heads per platter (one for the top surface and one for the bottom
surface).
5. Data is stored in concentric, circular tracks; each track is broken up into sectors.
6. A map of the sectors is stored on the HDD and is known as a file allocation table (FAT);
when the computer wants to store new data, it looks at the FAT map to find out which
sectors are free and then moves the read/write heads to the correct location
Uses of fixed hard disk drives
1. To store the operating system, systems software and working data/files.
2. Storing applications software.
3. Used in real-time systems (for example control of a chemical plant) and in online
systems (for example, booking airline tickets).
4. Used in file servers for computer networks.
Advantages of fixed hard disk drives Disadvantages of fixed hard disk drives
They have a very fast data transfer rate They can be fairly easily damaged (for
and fast access times to data. example, if shut down incorrectly
They have very large memory They have many moving parts which
capacities. can affect their overall reliability.
Their read/write operation can be noisy
when compared to solid-state drives.
Portable hard disk drives
A portable hard disk drive (HDD) is an external storage device that is designed to be easily
portable and used with multiple computers or devices.
Uses of portable hard disk drives
3. Storage devices and media 2
