Monday, 18 May 2015 00:00

HDD: dictionary of terms

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b2ap3_thumbnail_iStock_000015762740XSmall.jpgDictionary of terms

Because some components of hard disk drive that play a key role in its operation are usually perceived as an abstract concepts, below you will find a list and description of the most important terms that will make things clear about hard disk drive.

Aссes time — a period of time required by the drive on hard disk to seek and transfer data from or into the memory. Speed of drives based on hard magnetic disks is usually determined with access time (fetch time).

Сluster — smallest unit of space with which file allocation table works. As rule, cluster consists of 2-4-8 or more sectors.

Number of sectors depends on the type of disk. Searching clusters instead of separate sectors reduces OS' overhead time. Large clusters ensure faster operation of hard disk drive because the number of clusters in this case is less but at the same time the space on a disk is used less efficiently since many files may be less than a cluster and the remaining bytes of a cluster are not used.

Сontroller — circuits, usually located on the daughter board, that ensure management of the drive on hard disk, including movements of head and data reads and writes.

Сylinder — oppositely facing tracks on all sides of disks.

Drive head — a mechanism that moves around hard disk surface and ensures electromagnetic data read or write.

File Alloсation Table (FAT) — a record made by OS that monitors allocation of each file on the disk and which sectors are used and which are free to record new data to them.

Head gap — distance between the drive head and disk surface.

Interleave — correlation between the rotation speed of disk and organization of sectors on the disk. Usually disk rotation speed exceeds the ability of a computer to receive data from the disk. By the moment when controller reads data the following sequential sector already passes the head. That is why data is written to disk over one or two sectors. With special software you can modify the order of sequence during disk formatting.

Logiсal drive — certain parts of work surface of hard disk that are viewed as separate drives. Some logical drives can be used for other operating systems, such as UNIX.

Parking — moving heads of drive to a certain point and fixing them in a stable position over not used part of disk in order to minimize damage in case shock, when heads hit disk surfaces.

Partitioning – an operation of partitioning hard disk onto logical disks. All disks are partitioned, although smaller disks can have only one partition.

Platter — metal disk covered with magnetic material to which data is recorded. As rule, a drive based on hard disks has over one platter.

RLL (Run-length-limited) — a coding circuit used by some controllers to increase the number of sectors per track to fit more data.

Seсtor — division of disk tracks representing the main unit of size used by drive. OS sectors usually contain 512 bytes.

Seek time — time needed by head to move from one track to another track.

Traсk — concentric division of disk. Tracks are similar to tracks on vinyl plate. In contrast to vinyl's tracks that are continuous spiral, disk tracks have shape of a circle.Tracks are divided into clusters and sectors.

Traсk-to-traсk seek time — time required by drive head to move to the adjacent track.

Data transfer rate — volume of information transferred between the disk and computer per unit time. It includes track seek time.

More interesting material on hard disk drives will follow soon.

Last modified on Monday, 18 May 2015 16:24
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Viktor S., Ph.D. (Electrical/Computer Engineering), was hired by DataRecoup, the international data recovery corporation, in 2012. Promoted to Engineering Senior Manager in 2010 and then to his current position, as C.I.O. of DataRecoup, in 2014. Responsible for the management of critical, high-priority RAID data recovery cases and the application of his expert, comprehensive knowledge in database data retrieval. He is also responsible for planning and implementing SEO/SEM and other internet-based marketing strategies. Currently, Viktor S., Ph.D., is focusing on the further development and expansion of DataRecoup’s major internet marketing campaign for their already successful proprietary software application “Data Recovery for Windows” (an application which he developed).

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