What is a computer?

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Computer Notes for Grade 11 final copy

Tracks are concentric circles on a disk surface.

Sectors are pie shaped sections on the disk.

The area of intersection between a track and a sector is called the track sector. Data is recorded along the track, within the sector. Sectors are usually accessed in groups called clusters. A cluster is a set of track sectors ranging from 2 to 32. The storage area on a Hard Disks are a set of hard metal disks mounted on a spindle. A cylinder is a set of matched tracks on all the disks.

A read /write head is a device that reads data and writes data to a magnetic disk. An access arm is a mechanical arm that moves the read/write head across the surface of the disk as directed by the operating system.

Seek time - Time taken to move the heads to the track.

Access Time- Seek time + rotational delay.

Rotational Delay- Time it takes the disk to rotate to a particular sector.
Optical Disk

This is a secondary storage, on which enormous quantities of information are stored, by using a laser to burn microscopic holes on the surface of a hard plastic disk. A lower power laser reads the disk by reflecting light off the disk surface. The reflected light is converted into a series of bits that the computer can process. Eg. Compact Disk CDs and DVDs.
Compact Disk

This is a smaller optical disk. They use the same laser technology used for CD-ROM disk that have become popular for recorded music.

CD-ROM: CD-ROM stands for Compact Disk–Read Only Memory. It is used to store a wide variety of information. Its main advantage is that, it is portable and can hold a large amount of data. The storage capacity of most CD-ROMs is approximately 650 MB or 700 MB.

CD-ROMs have the following variations:

CD-R (Compact disc Recordable): Data can be written onto it just once. The stored data can then be read. Data once written onto it cannot be erased.

CD-RW (Compact disc Rewritable): It is also called erasable CD. Data once written onto it can be erased, to write or record new information many times.

DVD: DVD stands for Digital Versatile Disc. It can store larger amounts of data than a CD-ROM, with a storage capacity of 4.7MB up to 17GBs. DVDs are used to store very large multimedia presentations and movies that combine high quality sound and graphics.

Variations to DVD:

DVD-ROM, because data can only be read and not written nor erased. Blank recordable DVD discs (DVD-R) can be recorded once using a DVD recorder and then function as a DVD-ROM. Rewritable DVDs (DVD-RWand DVD-RAM) can be recorded and erased multiple times.

Blu-ray is an optical disc format designed to display high definition video and store large amounts of data. Its IIIthT the name comes from the fact that a blue laser reads from and writes to the disc rather than the red laser of DVD players. Blu-ray's storage capacity is enough to store a backup copy of most

people's hard drives. Blu-ray discs needs Blu-ray players to read the discs.

Magneto Optical Disk is an erasable optical drive, which uses magnetic optical technology in which a magnetic field changes the polarity of a spot on the disk that has been heated by a laser. Due to its tremendous storage capacities, it used to store catalogs.
Flash memory is a type of constantly-powered nonvolatile memory that can be erased and reprogrammed in units of memory called blocks. It is a variation of electrically erasable programmable read-only memory (EEPROM)

Flash Drive: A small, portable flash memory card that plugs into a computer USB port and functions as a portable hard drive. USB flash drives are easy-to-use as they can plug into any computer with a USB drive and the computer automatically detects this device. USB flash drives have less storage capacity than an external hard drive, but they are smaller and more durable. They come in various storage capacities of 2GB, 4GB, 8GB etc.

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