3.4. Information storage

A device designed for long-term storage of large amounts of information is called a storage device or external storage device, a mass storage device.

Depending on the placement in the PC distinguish drives:

1) external, which are outside the system unit and have their own housing, power supply, as well as a switch and cable;

2) internal, which are located on the mounting rack of the computer system unit. These devices do not have their own case and are connected to the storage controller and PC power supply.

By recording method distinguish devices of random and sequential access.

The main types of disk drives include:

• floppy disk drives;

• hard disk drives (HDD), Winchester;

• drives on removable CDs.

In floppy disk drives (floppy disks) information is recorded along tracks divided into separate sectors. Intersector gaps exist between these sectors. Depending on the type of device and media and the way of marking the latter, the number of tracks and sectors and the size of the sector are selected.

The principle of operation of such drives is that the diskette, which is installed in the drive, rotates at a speed of 300–360 rpm, which ensures access to the desired sector. Writing special control information to a disc is called formatting.

Hard disk drives are several metal disks that are located on the same axis and are enclosed in a sealed metal case. These discs must be formatted before use. On hard drives, the information is located on tracks, and inside tracks - on sectors. The combination of tracks on a package of magnetic disks with the same numbers is called a cylinder.

Among the main characteristics of HDDs are:

• information capacity;

• recording density;

• number of tracks;

• access time (milliseconds);

• external overall dimensions;

• drives on rewritable compact discs;

• drives on removable magnetic disks of large capacity;

• drives on magneto-optical disks.

Such drives are connected to the system bus using a different type of interface, among which are connection elements and auxiliary control circuits needed to connect devices.

Drives on removable CDs are used when using multimedia systems. These drives (CD-ROM) are adapted to read information from CDs that hold up to 700 MB. Recording on such discs is carried out once with the help of special equipment.

Drives on rewritable compact discs CD-RW, unlike drives on SB ^ disks, allow the use of multiple rewrites.

Storage devices on removable high-capacity magnetic disks are designed to record up to 200 MB of information and more to a removable disk.

Magneto-optical disk drives use the original scheme of reading and writing information that provides high information capacity of the media and reliable storage of the recorded information. Writing to these media is long-term, and reading is fast enough.

Devices for recording and reading digital information on a tape cassette are called tape drives. They are tape drives. They are used for backup archiving information. Among the positive qualities of such records are large amounts of stored information and low cost of data storage.