1. Secondary Storage Devices

2. Magnetic Tape Cassette Tape Magnetic medium (Ferromagnetic material, FeO) Plastic base If the magnetic material is exposed to a magnetic field, then it can permanently magnetised by this field. In a 90 minute cassette tape, there will be 135 metres of magnetic tape running at 4.76 cm/s across the roller.

3. Secondary Storage Devices Magnetic Tape The magnetic tape passes under an iron coil in a linear motion. It continues to move with a series of N-S and S-N polarities that are stored on the magnetic material. As the tape moves, an induced magnetic field is set up in the iron core. The changes in this induced magnetic field causes a changing current (voltage). Magnetic tape causing electric charge to flow Magnetic Head This shows the spools and the read/write head of the tape.

4. Secondary Storage Devices Hard disk The hard disk works on similar lines to the magnetic tape, using a magnetic medium to store data. Magnetic tape causing electric charge to flow 1.The material used in magnetic tape is a flimsy, bendy plastic material. In a hard drive it is hard and polished on a high precision aluminium or glass disk. The size of data therefore can be stored in very small domains 2.The read/write head using a magnetic tape touches the surface of the tape. On the hard drive it hovers a fraction above the surface. 3.The read/write head on a magnetic tape device moves about 4.76cm/sec, so sequential searching makes finding data slow. Contrast this with the hard drive, that spins at 170mph (or 7501cm/sec) and retrieving data appears instant. However, there are some crucial differences: Hard disk

5. Secondary Storage Devices Hard disk The hard disk works on similar lines to the magnetic tape, using a magnetic medium to store data. Read/write head How the read/write head identifies the data. The read/write head hovers over the platter (eg 10s nm above) and Aluminium alloy or glass about Magnetic material (10-20nm) Read/write head 2mm by 3mm

6. Secondary Storage Devices Hard disk The diagram below shows how data is accessed in more detail.