7. Define the following terms: Platters, Tracks, Sectors, Pits
Answers
Answer:
Disk s is used for storing large amounts of data. The most basic unit of data on the disk is a single bit of information. By magnetizing a area on disk in certain ways, one can make it represent a bit value of either 0 or 1. To code information, bits are grouped into bytes. Byte sizes are typically 4 to 8 bits, depending on the computer and the device. We assume that one character is stored in a single byte, and we use the terms byte and character interchangeably. The capacity of a disk is the number of bytes it can store, which is usually very large. Small floppy disks used with microcomputers typically hold from 400 kbytes to 1.5 Mbytes; hard disks for micros typically hold from several hundred Mbytes up to a few Gbytes. Whatever their capacity, disks are all made of magnetic material shaped as a thin circular disk and protected by a plastic or acrylic cover. A disk is single-sided if it stores information on only one of its surface and double-sided if both surfaces are used.
Disk Packs:
To increase storage capacity, disks are assembled into a disk pack, which may include many disks and hence many surfaces. A Disk pack is a layered grouping of hard disk platters (circular, rigid discs coated with a magnetic data storage surface). Disk pack is the core component of a hard disk drive. In modern hard disks, the disk pack is permanently sealed inside the drive. In many early hard disks, the disk pack was a removable unit, and would be supplied with a protective canister featuring a lifting handle.
Track and cylinder:
The (circular) area on a disk platter which can be accessed without moving the access arm of the drive is called track. Information is stored on a disk surface in concentric circles of small width, for each having a distinct diameter. Each circle is called a track. For disk
packs, the tracks with the same diameter on the various surfaces are called cylinder because of the shape they would form if connected in space. The set of tracks of a disk drive which can be accessed without changing the position of the access arm are called cylinder.
The number of tracks on a disk range from a few hundred to a few thousand, and the capacity of each track typically range from tens of Kbytes to 150 Kbytes.
Sector:
A fixed size physical data block on a disk drive.
A track usually contains a large amount of information; it is divided into smaller blocks or sectors. The division of a track into sectors is hard-coded on the disk surface and cannot be changed. One type of sector organization calls a portion of a track that subtends a fixed angle at the center as a sector. Several other sector organizations are possible, one of which is to have the sectors subtend smaller angles at the center as one moves away, thus maintaining a uniform density of recording.
Block and Interblock Gaps:
A physical data record, separated on the medium from other blocks by inter-block gaps is called block. The division of a track into equal sized disk blocks is set by the operating system during disk formatting. Block size is fixed during initialization and cannot be changed dynamically. Typical disk block sizes range from 512 to 4096 bytes. A disk with hard coded sectors often has the sectors subdivided into blocks during initialization.
An area between data blocks which contains no data and which separates the blocks is called interblock gap.
Blocks are separated by fixed size interblock gaps, which include specially coded control information written during disk initialization. This information is used to determine which block on the track follows each interblock gap.
Read/write Head:
A tape drive is required to read the data from or to write the data to a tape reel. Usually, each group of bits that forms a byte is stored across the tape, and the bytes themselves are stored consecutively on the tape. A read/write head is used to read or write data on tape. Data records on tape are also stored in blocks-although the blocks may be substantially larger than those for disks, and interblock gaps are also quite large. With typical tape densities of 1600 to 6250 bytes per inch, a typical interblock gap of 0.6 inches corresponds to 960 to 3750 bytes of wasted storage space.
Explanation: