Hard disk drive definition
hard disk drive is an essential and still probably the most mysterious component of a personal computer device. A hard disk drive is actually a closed device that your Computer uses for nonvolatile data storage. Nonvolatile, as well as semi permanent, storage space means that the actual storage space device keeps the information no matter if absolutely no electrical power is supplied to the pc. Because of the hard disk drive is expected to keep information until they are intentionally deleted or just over-written, the hard drive is needed to carry necessary computer programming along with data. Consequently, once the disk drive does not work properly, the effects are generally extremely serious. To keep, service, and upgrade your personal computer system correctly, you must learn the hard drive works.
Hard disk heads and platters.
A hard disk drive consists of solid, disk-shaped platters, normally made of aluminium or possibly glass (look at picture). Not like diskettes, this platters cannot bend or flex hence the term hard drive. For most hard disk drives, you cannot take off the platters, and that’s why they’re often known as fixed disk drives. External hard drives are offered also. Generally, this kind of term describes a device where the whole hard drive device (that’s, this disk unit that consists of a platters along with the entire drive) is removable, however it may also refer to cartridge drives, in which the platters usually are built into a removable cartridge.
Note :
Hard disk drives in many cases are known as Winchester drives. The following term goes back to 1973, once Ibm released the type 3340 hard drive, that have 30MB of fixed platter together with 30MB of detachable platter storage with individual spindles. The particular drive was initially code named Winchester by project leader Ken Haughton because the original total capacity designation (30-30) seemed just like the well-known .30-30 (caliber-grains of charge) cartridge applied by the Winchester 94 rifle launched in 1895. An original 3340 “Winchester” drive appeared to be the first one to work with a closed head/disk assembly, and also the name has since been used on all of subsequent hard drives using the same technology.
The principle of hard drives:
Basic principle of hard drives and floppy disks work are almost identical: the data is written and read by the universal read-write heads from the surfaces of the rotating magnetic disk, divided into tracks and sectors (512 bytes each), as in Fig. 1
In storage rings are usually installed multiple drives, and data is written on both sides of each of them. Most drives have at least two or three discs (which can record on four or six sides),
but there are also devices that contain up to 11 or more disks. The same type of (equally spaced) on all sides of the track drives are combined into a cylinder. To each side of each disc provides its own track read / write, but all the heads are mounted on a common shaft or a rack. For this reason, the head can not move independently of each other and move only synchronously.
Hard drives spin faster than flexible. The frequency of their rotation, even in pain in most of the first models was 3600 rev / min (ie 10 times more than in the floppy disk), and until recently was almost a standard for hard drives, but now speed drives increased, for example, on my laptop drive capacity 3.3 GB rotates with a frequency of 4852 rev / min, but there are models with frequencies 5400, 5600, 6400, 7200 and even 10 000 rev / min. The rate of work of a hard drive depends on the frequency of its rotation, the velocity of the system heads, and the number of sectors per track. In addition, due to a combination of all these factors to communicate with hard disk drives is much faster than floppy disks.
What isTrack and sector in Harddrive.
HARDISK TRACK AND SECTOR EXPLAINED.
Track – this is one “ring” of the data on one side of the disk. Track record on the disk is too large to use as unit of information storage. In many drives, the capacity of more than 100 thousand bytes, and gives the unit for storing small files are very wasteful. Therefore, the tracks on the disk is divided into numbered segments called sectors.
The number of sectors may be different depending on the density of tracks and the drive type. For example, the track floppy drives can hold from 8 to 36 sectors, and track the hard drive – 380 to 700. Sectors that are created using standard programming format, have a capacity of 512 bytes, but it is possible that in the future, this value will change.
The numbering of sectors per track begins with unity, in contrast to the heads and cylinders, which is counting from zero. For example, a floppy disk HD (High Density) format 3.5-inch (1.44 MB) contains 80 cylinders, numbered 0 to 79 in the drive has two heads (with numbers 0 and 1), and each track is divided into the cylinder at 18 sectors (1-18).
When you format a disk at the beginning and end of each sector are additional areas to record their numbers, and other service information, through which the controller identifies the beginning and end of the sector. This allows us to distinguish an unformatted and formatted the disk space. After formatting the disk capacity is reduced, and this has to be reconciled, as to ensure normal operation of the drive for a disk space should be reserved for official information.
At the beginning of each sector recorded its title (or a prefix – prefix portion), that determines the beginning and the sector number, and in the end – the conclusion (or suffix – suffix portion), which contains a checksum (checksum), necessary to verify data integrity . Most new drives instead of the title, so-called entry No-ID, accommodating a larger amount of data. In addition to these areas of service data, each sector contains a data area of 512 bytes. When low-level (physical) formatting to all data bytes assigned a value, for example F6h.
