Hard Disk - Glossary

ASCII
ASCII is the abbreviation for American Standard Code of Information Interchange. A 7-bit code standard for representation of characters, numbers, symbols and control characters, for use in data communication and data storage.

AT/ATA
Name of standard interface and protocol for hard drives.

Backup
The process of creating a copy of data or files for later retrieval in case of original data loss.

BIOS
Abbreviated for Basic Input Output System. A chip within the PC on the mother board that offers basic input and output services to all attached devices.

Bit
An abbreviation for a binary digit. The basic information unit within a computer. A bit can take on one of two values, normally represented by '0' and '1'. Value ‘0’ of bit also called OFF and ‘1’ as ON state.

Bit Density
Bits Per Inch. The number of bits that can be written along one inch of a track.

BOD
Beginning Of Data. Electronic or magnetic sign shows the start of the data on the tape.

BOM
Beginning Of Media. Electronic or magnetic sign, signals the beginning of media.

Boot
To start or restart your computer; loading the operating system.

Boot Record
A file system table, containing information about bootable partition i.e. which contains operating system. (Often referred to as Boot sector, Boot block or Boot Track).

Buffer
A storage device or area on a storage device, which holds data temporarily, until needed for processing or printing. A buffer can also be used to aid communication between two devices with very different processing speeds (such as two modems, or the CPU and the printer).

Bus
A collection of wires through which data is transmitted from one part of a computer to another. Examples are IDE interface cable and a SCSI cable.

Byte
A byte is a series of 8 bits. Also called a Octet. A byte is able to store one character. Computer storage space is measured in bytes.

Capacity
The amount of data or information, measured in bytes that can be stored on a hard drive or any storage media. Also known as storage capacity.

CD
Compact Disk. Optical storage device for storing data and multimedia contents.

Cluster
Cluster is a basic allocation unit on a hard drive. It is a group of contiguous sectors. The cluster size (number of sectors per cluster) varies with the storage media and is fixed at time of format. At least one cluster is allocated to each file, regardless of the file's size, that is stored in the DOS environment.

Computer Virus
A computer program with the characteristic feature of being able to generate copies of itself, and thereby spreading. It is usually known as a dangerous program which is able to perform some harmful tasks.

Cylinder
On a drive, the same number tracks on all platters make a cylinder.

Data Block
A series of data elements handled as one unit. Typically a data block on disk is 512 bytes long.

Data compression
The storing of data in a manner that requires less space on the storage medium.

Data Recovery
To recover the lost or damaged data. Data can be loss by media crash or accidentally file deleted. Whatever the case is, optimum data recovery, Inc. always recovers your data.

Database
Database is an organized collection of information stored on a computer. The database contents can easily be accessed, managed and updated.

Deleted File
A file that has been logically, but not physically erased from the operating system using delete command. It can be recovered lately, if not over written by any other data. Optimum recovery provides services to recover deleted or crashed files.

Directory
A directory, catalog, or folder, is an entity in a file system which contains a group of files and other directories.

Disk
Disk is a general term that is used to describe flattened circular objects. Mostly it is used for round disk. In computer, any rounded media is known as disk. For example, hard disk, floppy disk and compact disk.

Disk Crash
The term is used for any problem with the disk, usually hard disk. If hard disk is not able to read/write, it is known as hard disk crash. More specifically it is called head crash.

Driver
A small software program that controls specific device. Every device has its own driver, for example printer and modem. The driver software is not for the end user else it tells the computer how to interact with the specific device.

DVD
Digital Versatile Disc, a type of optical disk similar to the CD-ROM but with much greater storage capacity. DVDs are similar in appearance to compact discs but one DVD holds a minimum of 4.7 GB data.

Encryption
Encryption is process of modifying data in a way that unauthorized persons can not read that. The reverse process of encryption is known as decryption.

EOD
End Of Data. Electronic or magnetic sign shows the end of the data on the magnetic tape.

EOM
End Of Media. Electronic or magnetic sign tells the physical end of the tape.

FAT
File Allocation Table. It contains information about where on the disk the content of the files are stored.

FAT16
Older version of the FAT file system. It is a 16-bit file allocation system. It has a limitation with respect to the size of partitions it can handle.

FAT32
Newer version of the FAT file system, based on 32-bit integers. The file system is able to handle partitions of 2 TB size and uses the storage capacity more efficiently than FAT16.

Fdisk
A software utility used to partition a hard drive. This utility is included with DOS and Windows 95 operating systems.

File
Data stored as a named unit on a data storage medium. Examples: a program, a document, a database.

File System
A system for organising and cataloguing files on a data storage media, comparable to the index in a book. Examples: FAT16, FAT32, NTFS, HPFS, S51K, ext2, AFS.

Floppy Disk (FD)
Low capacity storage media with soft kernel/base, hence the name floppy.

Floppy Interface
Interface where the floppy drive is connected to the computer. Some tape drives also connect to this interface.

Fly Height
Distance between read/write head and the media surface whilst the motor is rotating (hard drive).

Format
Structure or composition of a file (file format) or the logical layout of a data storage unit.

Formatted Capacity
The actual capacity available to store data in a mass storage device.The formatted capacity is the gross capacity minus the capacity taken up by the overhead data required for formatting the media.

Fragmented
In parts. A fragmented file does not have its content stored sequentially on the media. The files content may be stored in small segments scattered over an area of the disk. The file system keeps track of where one the media the data is stored and the user will normally not notice that a file is fragmented. Fragmentation is common on hard drives, but usually data is stored sequentially on tape.

Free Space
Free space in a storage device. The space that in any given time does not belong to any file or the file system itself (system information). New files will be stored in the free space area.

Gigabyte(GB)
Expression used to describe storage capacity or amount of data. One gigabyte is about 1000 millions of bytes/characters (10243).

G-List
Growing Defect List. List of blocks/sector of a disk that has become defective during the lifetime of the disk. The list is updated by the drive itself and stored internally on the disk. The information in this list may indicate the current state of the drive. Many entries in the G-List may indicate an early stat of a head crash.

Hard Disk (HD)
Medium for permanent storage of data. Magnetic platters, electronics and mechanics make up a hard disk. The platters are fixed to a spindle. On each side of a platter there is a read/write head. Each platter is divided in to tracks, which again is divided into sectors. A characteristic with hard disks is that the platters and the mechanics are in an airtight enclosure, and that the read/write heads do not touch the platters as long as the platters are rotating. See fly height.

Hard Drive
See hard disk.

Hard Error
An error that is repeatable every time the same area on a disk is accessed.

Hardware
The physical components that computer system is comprised of, like had disk, screen, expansion cards etc.

HDA
Head Disk Assembly. For today's drives this corresponds to the hard disk without the PCB.

Head
Head often refered to as the read/write head.

Head Crash
A head crash is the damage caused by the heads coming in contact with the magnetic surface of the media (platters). The crash causes damage to the read heads and scratches in the magnetic coating. Data that was stored in the scratched area cannot be recovered. Shavings and dust from one head crash may cause crashes on the other surfaces.

IDE
Integrated Drive Electronics. Standard interface and protocol for hard disks. The disk controller is an integrated part of the hard disk unit.

Image
A cloned copy of storage device.

Interface
Defined/standard transition/link - hardware or software. Rules for communicating with a unit. Example: See SCSI. (User interface) The 'face' of the computer. The part of the operating system that the user communicates with directly.

Jumper
A jumper is an electrically conductive component that you place over pairs of pins to connect them electronically. For example, a jumper is one way to designate a hard drive as master or slave.

Kilobyte (KB)
Expression used to describe storage capacity or amount of data. One kilobyte is 1024 bytes/characters.

Logical Damage
Damage to file system or file data (file content).

Logical Recovery
The recovery work performed on a copy of the raw data from the damaged unit. The intention is to repair damages to the file system or files, and to make the files available to the customer.

Logical Storage Unit
A storage unit made up by one or several parts of a physical unit, or several physical units, or a combination. A logical storage unit acts as one independent unit. Examples: partition, volume.

Low Temperature
Unpacking drives at or below 10° C involves a risk of condensation damage to the hard disk. A hard disk that holds a temperature of 4° C should be allowed to stabilise for 13 hours before unpacking.

Master
The first drive in a dual drive combination. A master drive by itself (with no slave) is called a single drive. See slave.

Master Boot Record (MBR)
The first sector of a hard disk in a PC. It contains the Partition Table.

Megabyte (MB)
Expression used to describe storage capacity or amount of data. One megabyte is about one million of bytes/characters (10242).

Mirror
Same as clone copy.

Mirror Copy
Identical copy. Block by block copy of all blocks in a storage medium.

Mirroring
Creating an exact mirror data copy.

MTBF (Mean Time Between Failures)
Average time (expressed in hours) that a component works without failure. Also, the length of time a user may reasonably expect a device or system to work before an incapacitating fault occurs.

No Physical Damage
No physical damage in the drive itself was identified during physical analysis. All raw data from the drive may be copied to other storage medium without loss.

NTFS
The file system designed to the operating system Windows NT. This file system is more advanced than the FAT file system used by the earlier Windows operating systems, with regards to data structures, filenames, security and access control.

Off Track
Used when the read/write head is unable to follow the right track. In hard disks this may be a result of a shock (shock damage). In tape context this may be due to mechanical problems with the tape drive.

Operating System
The operating system is the most basic program in a computer. All computers have an operating system that among other things is used for starting the computer and running other programs (application programs). The operating system performs important tasks like receiving input from the keyboard and mouse, sending information to the screen, keeping track of files and directories on the disk, as well as controlling the various units such as disks printers etc-. An operating system also offers a user interface, giving the user the possibility to control the computer. Examples of operating systems are: Windows95/98, Windows NT/2000, Novell Netware, Mac OS, UNIX, Linux.

Overwritten Data
This refers to data, which has been physically overwritten by other data. Data that is physically overwritten by other data cannot be recovered.

Park Area
A designated save non-data landing area designated for the resting of read/write head when drive power is turnd off and not in use.

Partition
Logical storage unit. One hard disk can be divided into one or more partitions. Each partition is regarded as one logical storage unit, and normally contains one file system. In the Windows operating systems (95/98/NT/2000) each partition is assigned one station letter (C:, D: etc). For the user it looks like there are several hard disks in the computer. The term partition may also be used in tape context, but the interpretation differs slightly. On may have to partitions on tape. One will contain the file data and the other the system information.

Partition Table
A file system table. It contains information of how many and which types of partitions are on the disk.

PCB
Printed Circuit Board. Used for the electronics board on the hard drive.

Physical Damage
Damage to the physical unit. For a hard drive this may be damage to the electronics, the mechanics or the media itself.

Physical Recovery
The work performed directly on the damaged unit. The intention is to transfer as much data as possible to a functional storage unit.

Platter
The actual storage media in the different type of disk. In the hard drive the platter have a core of glass or aluminum, covered with a thin layer of Ferric oxide or an Cobalt alloy (Co-Ni, Co-Cr, Co-Ni-W). This layer is protected by a layer of a very hard material (overcoat), and a thin layer of lubricant. A CD is a plastic disc in which the data is impressed. It has a metallic, reflecting backside.

RAID
Redundant Array of Independent (or Inexpensive) Disks. A collection of 2 or more disks that work together to increase performance and safety. The disks form one logical storage unit. The most used RAID levels are: RAID 0: striping only, RAID 1: mirroring only, RAID 5: striping with error correction information on all disks.

RAM
Random Access Memory. Memory that allows any storage location to be accessed randomly, as opposed to tape drives, which are sequential access devices. Chips in the computer used for temporary storage of data.

Raw Data
Raw data is uninterrupted data from a storage medium. The maximum amount of raw data that can be copied from a storage medium equals the capacity of the medium. As raw data, the data is handled without considering the information stored within the data. When handling raw data one does not know how munch of that disk is actually in use or free. Not until the data is interpreted trough a file system, will there be access to directories or files.

Read/Write Head
Element use to create and access the information stored magnetically on the platters/tape. A drive with several disk surfaces or platters will have a separate head for each data surface.

Reading Problems
Due to small damages in the magnetic coating of the platters, one or several sectors or groups of sectors may be damaged beyond rescue. This may be a result of rough handling of the disk during transport or installation. See shock damage.

ROM
Read Only Memory. A storage media that can be read only - not written to (except for the first time).

SATA
Serial ATA is an evolutionary replacement for the Parallel ATA physical storage interface.

SCSI
Small Computer Systems Interface. A standard interface for connecting external units like disks, tape drives, CD players, scanners etc to a computer. Usually pronounced as "scuzzy."

Sector
Smallest data unit accessible on disk. Normally 512 bytes. See block.

Server
A computer used primarily to store data and providing access to shared resources. Usually it contains a network operating system.

Session
A session on tape corresponds to a partition or volume on hard disk.

Shock Damage
Shock to a hard drive may cause the platters to become displaced, or damage to heads or the magnetic coating of the platters. Dropping a hard drive may also damage to the mechanics within the drive such as the motor. As a consequence, the drive is unable to position the heads correctly along the recorded signals. A shock may later lead to a head crash.

Slave
The second drive in a dual drive combination. See master.

Soft Error
An error that occurs occasionally when attempting to read/write the same location. A non-repeatable error.

Software
General expression used to describe a collection of instructions enabling a computer to solve one or several tasks.

Spindle Motor
The motor within a hard drive that rotates the platters.

Storage Medium
Collective description of all types of media used for data storage. Examples: hard disk, floppy disk, MO, streamer tape, DAT, DLT, CD.

Stripe Set
Collection of disks that together, trough striping, makes up one unit.

Striping
Spreading data over several disks on a bit, byte or cylinder level. The intention is to improve performance, through letting positioning and read/write operations overlap in time.

Super Block
The first block of an UNIX-file system. It contains for instance the configuration of the file system.

Surface
The top or the bottom side of a platter coated with a magnetic material required recording data. A platter may use one or both surfaces to store data.

System Information
Typically used about the internal information of the file system itself. The file system keeps track of the names of the files, their size and where the file is stored. This information is stored to the media in addition to the file content.

Tape
Magnetic tape, in cartridge or reel. The tape has a magnetic surface where data may be stored. Tape is often used as backup media. Examples are: DAT, Streamer tape, DLT.

Terra Byte(TB)
Expression used to describe data storage capacity or amount of data. One terra byte corresponds to 10244 bytes/characters.

Track
Disk: Concentric circles where the data is stored, divided into sectors.
Tape: The tracks of the tape prepared for storage of data, divided into blocks. See format.

Unicode
A 16-bit code standard for uniform representation of all the characters systems of the world, digits, symbols and control sequences for use when storing data.

Volume
Logical storage unit. May also be called a partition.

Volume Set
Collection of disks or partitions that together forms one logical storage unit