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- DATA RECOVERY PROCESS: How does it work?
- HOW TO deal with a failed hard drive
- DATA LOSS: Why it happens and how to prevent it.
- WHAT IS data recovery?
- DATA RECOVERY and data storage guide
- GLOSSARY of Data Recovery
- DICTIONARY of hard drives
- LAYMAN'S GUIDE to data recovery
- WHAT IS COMPUTER FORENSICS - What is it?
| Analog signals | Signals which come directly from the read/write heads, before digitalisation. No analog signals indicate that no data has been stored on the media, or that the data has been removed using a strong magnetic field such as a Degausser. It differs from a digital signal in that small fluctuations in the signal are meaningful. |
| Areal Density | The number of bits of data that can be recorded onto the surface of a disk or platter usually measured in square inches. Areal density, also sometimes called bit density, refers to the amount of data that can be stored in a given amount of hard disk platter "real estate". Since disk platters surfaces are of course two-dimensional, areal density is a measure of the number of bits that can be stored in a unit of area. It is usually expressed in bits per square inch (BPSI). |
| ASCII | 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. ASCII codes represent text in computers, in other communications equipment, and in control devices that work with text. |
| AT/ATA | Name of standard interface and protocol for hard drives. See also IDE. Advanced Technology Attachment is generally used as a synonym for EIDE, as is UltraATA. |
| Backup | The process of creating a copy of programs or files for later retrieval. To create a copy of a disk’s contents on another location for safe keeping. Since hard drives are not infallible, it is recommended that you backup its contents regularly. |
| Backup copy | A copy of a program or file that is stored separately from the original. If the original files or media are lost, the backup copy may be used for recovery. A temporary copy of digital information made for recovery purposes. |
| BIOS | Basic Input Output System. A chip within the PC that offers basic input and output services to all attached devices. The function of the BIOS is so vital that the information on the BIOS is stored on a ROM chip separate from the hard drive to protect it from potential crashes. |
| 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'. See also byte. A measurement of data. It is the smallest unit of data. A bit is either the "1" or "0" component of the binary code. A collection of bits is put together to form a byte. |
| Bit density | Expressed as bits per inch (BPI), the number of bits that can be written onto one inch of track on a disk surface. Number of bits that can be placed, per unit area or volume, on a storage medium (eg bits per inch of magnetic tape). |
| BOD | Beginning Of Data. Electronic or magnetic sign, a part of the low-level format on tape. BOD signals the start of data. |
| BOM | Begining Of Media. Electronic or magnetic sign, a part of the low-level format on tape. BOM signals the beginning of media. |
| Boot | To start or restart your computer; loading the operating system. Because the computer gets itself up and going from an inert state, it could be said to lift itself up "by its own bootstraps" -- this is where the term 'boot' originates. |
| Boot Record | A file system table of the FAT and NTFS file systems, containing information about one partition. (Often refered to as Boot sector, Boot block or Boot Track). Once the BIOS determines which disk to boot from, it loads the first sector of that disk into memory and executes it. Besides this loader program, the Boot Record contains the partition table for that disk. If the Boot Record is damaged, it can be a very serious situation! |
| Buffer | Temporary data storage. Example: An area used to make up for a difference in data transfer rates and/or data processing rates between sender and receiver. A printer buffer copies data from the computer and holds it until the printer is ready to print. A routine or an area of storage that compensates for the different speeds of data flow or timings of events, when transferring data from one device to another. |
| Bus | The path that carries data between the computer (microprocessor) and peripheral devices. An IDE interface cable and a SCSI cable are both examples of a bus. A set of parallel wires or PCB tracks along which data is transmitted in a computer system - the width of the bus refers to the number of parallel tracks - the wider the bus, the faster data can be transmitted down it. |
| Byte | A byte is a series of 8 bits. Also called a character. Computer storage space is measured in bytes. A kilobyte (or 1 KB) represents 1024 bytes. A megabyte (1 MB) represents 1024 KB. A gigabyte represents 1024 MB. 8-bit information unit, able to hold information of one character/digit magnitude. |
| Capacity | The amount of information, measured in bytes that can be stored on a hard drive. Also known as storage capacity. The amount of space inside a container provided for a given amount of product. |
| CD | Compact Disk. Optical storage device for storing data and sound. Also see platter. Compact Disk. A media that uses a single track, like phongraph records. This layout of data makes random access of data take longer, this is commonly referred to as a long seek time. CD's have a capacity of 700MB (depending upon the disc). |
| Clean room | An environmentally controlled, dust-free environment in which hard drives are assembled or opened for internal inspection or servicing. These are the facilities used to assemble or service hard disks. They are environmentally controlled and dust-free. |
| Cluster | A cluster is defined as an allocation unit. It is a group of sectors. Most file systems group sectors together and handle the group as one unit. 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. Windows allocates space to files in units called clusters. Each cluster contains from 1 to 64 sectors, depending on the type and size of the disk. A cluster is the smallest unit of disk space that can be allocated for use by files. |
| Computer crash | A crash in computing is a condition where a program (either an application or part of the operating system) stops performing its expected function and also stops responding to other parts of the system. Often the offending program may simply appear to freeze. If this program is a critical part of the operating system kernel the entire computer may crash (a system crash). |
| Computer Virus | A dangerous computer program with the characteristic feature of being able to generate copies of itself, and thereby spreading. Additionally most computer viruses have a destructive payload that is activated under certain conditions. A computer virus is a self-replicating program containing code that explicitly copies itself and can "infect" other programs by modifying them or their environment such that a call to an infected program implies a call to a (possibly evolved) copy of the virus. |
| Corrupt copy | Some times while transferring data from a damaged disk, the damaged disk releases the expected amount of raw data but in a seemingly random order. Such a copy is worthless. The problem is due to a physical damage to the disk, which causes errors in the location/addressing information. |
| Cylinder | On a disk, all tracks with the same radius are referred to as a cylinder. The cylindrical surface formed by identical track numbers on vertically stacked discs. At any location of the head positioning arm, all tracks under all heads are the cylinder. The cylinder number is one of the three address components required to find a specific address. The other two are head number and sector number. |
| Data block | A series of data elements handled as one unit. Typically a data block on disk is 512 bytes long (synonymous with sector). On tape the block size is normally greater and variable. A sequence of continuous data character or bytes transmitted as a unit. |
| Data compression | Reducing the size of a file or data in general. Several compression techniques are use to save time during transfer/communication or space during storage. Reducing the amount of electronic "space" data takes up. Methods include replacing blank spaces with a character count, or replacing redundant data with shorter stand-in "codes". No matter how data is compressed, it must be decompressed before it can be used. |
| Data Destruction | Removal/destruction of information stored on a storage medium. Data remanence is the residual physical representation of data that has been in some way erased. After storage media is erased there may be some physical characteristics that allow data to be reconstructed. |
| Data Recovery | The salvaging of data stored on damaged media , such as magnetic disks and tapes Dataleach specialises in data recovery service and our specialists and engineers can often restore a surprisingly high percentage of the data on damaged media. Making previously lost or damaged data available. Examples: A file that was deleted by accident can normally be recovered. Quartz can normally recover the files from a disk physically damaged by shock. |
| Database | A database as an electronic filing collection of information that is organized so that it can easily be accessed, managed, and updated. A collection of information arranged into individual records to be searched by computer. |
| Decode | Transforming encoded information into information that is readable to a program or a user. To convert digital information to a form capable of being reproduced in the way intended by the content provider. |
| Defect Management | A general methodology of eliminating data errors on a recording surface by mapping out known defects on the media. The defective areas are rendered inaccessible, so that when information is written to the disk, it is stored to non-defective locations on the disk. See G-List and P-List. A technique ensuring long-term data integrity. Defect management consists of scanning disk drives both at the factory and during regular use, deallocating defective sectors before purchase and compensating for new defective sectors afterward. |
| Degausser | Equipment employing a strong magnetic field to perform data erasure. A device that removes unwanted magnetism from monitors or the heads in a tape or disk drive mechanism. |
| Deleted file | When a file is deleted using the operating system command or Delete-key, it is only the reference to the file that is deleted. The space previously occupied by the file content will be free to be used by any new file. It is possible to recover the deleted file until a new file has occupied the space. A file that has been logically, but not necessarily physically, erased from the operating system, perhaps to eliminate potentially incriminating evidence. Deleting files does not always necessarily eliminate the possibility of recovering all or part of the original data. |
| Directory | A group of related files are stored under a common name, the directory name. This is similar to how grouped documents are stored between dividers when filed in a ring binder. In computing, a directory, catalog, or folder, is an entity in a file system which contains a group of files and other directories. A typical file system contains thousands of files, and directories help organize them by keeping related files together. A directory contained inside another directory is called a subdirectory of that directory. Together, the directories form a hierarchy, or tree structure. |
| Disk |
Used
synonymous with hard disk. Refers to the most common form of
data storage that uses disks of magnetized materials to save
data. Can be used about any storage media where the actual media is a circular disc - hard or soft kernel, magnetic or optical technology. Circular platters. The actual media. Se platter. |
| Disk crash | As a popular expression this term is used about almost any problem with the computer or the hard disk. More correctly it should be used synonymous with head crash. |
| Drive |
Often used synonymously with disk. For removable media, the term is used about the fixed housing unit. Examples: floppy drive, tape drive. A device containing motors, electronics and other gadgetry for storing (writing) and retrieving (reading) data on a disk. A hard disk drive is one which is generally not removable from the machine. A floppy disk drive accepts removable disk cartridges. |
| Driver |
(Software) Small, specialised
program that typically handles the exchange of information with
specific units/equipment like one type of printer (printer
driver). A set of software that contains instructions that
allows the computer to communicate with its peripheral devices.
(Hardware) Component, adapter, amplifier. Used about components working with high efficiencies, supplying power to motors etc. |
| Drop damage | Damage caused to a drive by dropping it. Dropping a hard drive may also damage to the mechanics within the drive such as the motor. See shock damage. |
| DVD | Digital Versatile Disk. A data storage media with platters similar to a CD. The storage capacity is much higher then for a CD. DVD us used for storing video, sound and data. Today most DVDs are used to display full-length commercial motion pictures, plus additional material such as outtakes, director's notes, movie trailers, etc. |
| Encryption | Modifying data, a file for example, to prevent unauthorised access to the information. A procedure that renders the contents of a message or file unintelligible to anyone not authorized to read it. |
| EOD | End Of Data. Electronic or magnetic sign, a part of the low-level format on tape. EOD signals the end of data. |
| EOM | End Of Media. Electronic or magnetic sign, a part of the low-level format on tape. EOM signals the physical end of the tape. |
| FAT | File Allocation Table. A file system table used by the FAT-file systems. It contains information about where on the disk the content of the files are stored. A cluster map listing locations of the sequential parts of each file. There are two copies of the FAT for each partition, located just after the volume boot record. |
| FAT16 | Older version of the FAT file system, based on 16-bit integers. It has a limitation with respect to the size of partitions it can handle. File Allocation Table (FAT) is a file system that was developed for MS-DOS and used in consumer versions of Microsoft Windows up to and including Windows Me. |
| 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. This term refers to the way Windows stores data on your hard drive. "FAT" stands for "File Allocation Table," which keeps track of all your files and helps the computer locate them on the disk. Even if a file gets fragmented (split up into various areas on the disk) the file allocation table still can keep track of it. FAT32 is an improvement to the original FAT system since it uses more bits to identify each cluster on the the disk. ... |
| Fdisk | A software utility used to partition a hard drive. This utility is included with DOS and Windows 95 operating systems. It can Display, Delete and Create partitions and logical drives, defining them for DOS, OS/2 or Windows, depending on which version of FDISK is used and how it is used. Type FDISK and hit Enter to start the program. This is a DESTRUCTIVE command and incorrect use will result in data loss! |
| File | Data stored as a named unit on a data storage medium. Examples: a program, a document, a database. A file in a computer system is a stream (sequence) of bits stored as a single unit, typically in a file system on disk or magnetic tape. |
| 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. A data structure that translates the physical (sector) view of a disc into a logical (files, directories) structure, which helps both computers and users locate files. In other words, it records where files and directories are located on the disc. See also Logical Format. |
| Firmware | Permanent instructions and data programmed directly into the circuitry of read-only memory for controlling the operation of the computer. Computer instructions which are permanently imbedded in the circuitry, usually in a ROM chip. |
| Floppy disk (FD) | Low capacity storage media with soft kernel/base, hence the name floppy. Storage medium for computer files consisting of a magnetic, flexible disk enclosed in a 3 1/2" square plastic case. Floppy disks may be formatted for use on both Macintosh or PC platforms. |
| 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. The pattern into which data are systematically arranged for use on a computer. A file format is the specific design of how information is organized in the file. |
| 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. This is the actual size of the hard drive minus the overhead data needed 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. When a file is not written to a disk in contiguous blocks. If there is not enough free space to write a full file to a disk in one continuous stream of blocks then the file gets split up between two or more parts of the disk surface. This is known as fragmenting and can make the time for loading a file longer as the disk has to seek for the rest of the file. |
| 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). 2 to the 30th power (1,073,741,824) bytes. One gigabyte is equal to 1,024 megabytes. Gigabyte is often abbreviated as G or GB. |
| 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. Fixed magnetic data storage disk providing high-speed access for high-speed data processing. |
| Hard drive | The mechanism that reads and writes data on a hard disk. Hard disk drives (HDDs) for PCs generally have seek times of about 12 milliseconds or less. Many disk drives improve their performance through a technique called caching. There are several interface standards for passing data between a hard disk and a computer. The most common are IDE and SCSI. |
| Hard Error | An error that is repeatable every time the same area on a disk is accessed. An error caused by a hardware failure or by accessing incompatible hardware; also, any error that prevents a program from continuing an operation. |
| Hardware | The physical components that computer system is comprised of, like had disk, screen, expansion cards etc. The physical equipment of computing and computer-directed activities. The physical components of a computer system. Contrast with software. |
| HDA | Head Disk Assembly. For today's drives this corresponds to the hard disk without the PCB. The mechanical portion of a rigid, fixed hard drive. It usually includes disks, heads, spindle motor, and actuator. |
| Head | often refered to as the read/write head. Hard disk heads are extremely small electromagnets that read and write binary data onto the spinning platters. Hard disk usually has more than one platter with one head on each sides. Head Crash - A hard disk failure in which a read/write head collides with the surface of the platter on which information is stored. In a hard disk, the read/write heads float less than a hair’s breadth over the surface of the platter as it spins |
| 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. |
| Header | Introductory, preliminary information. Example: system information (file name, type of file, file length etc.), may be stored just before or at the start of a file. The use of headers is typical for tape file systems, and the format of larger files like databases. |
| IDE | Integrated Drive Electronics. Standard interface and protocol for hard disks. The disk controller is an integrated part of the hard disk unit. A type of hard drive interface. Provided as standard on Risc PC motherboards. It can have up to two physical drives, configured as 'master' and 'slave'. |
| Image | A cloned copy of strage 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. The meeting point between a computer and something or (someone) outside of it. Common interfaces for peripherals are the serial and parallel ports. Common interfaces for people are the monitor screen and keyboard. |
| Invalid files | Artificial files, incorrectly created by automatic recovery utilities like Chkdsk, Scandisk, Vrepair, Norton Disk Doctor and many others. The content of such files does not normally have any value. This is because it may contain only a fragment of the data of the original file, or it may contain fragments of several files. |
| 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. A tiny connector box that can move between two pins in order to change electrical connectors. The two pins protrude from a circuit board and are electrically connected when the jumper is in place. |
| Kilobyte (KB) | Expression used to describe storage capacity or amount of data. One kilobyte is 1024 bytes/characters. As a measure of computer memory or storage, a kilobyte (KB or Kbyte*) is approximately a thousand bytes (actually, 2 to the 10th power, or decimal 1,024 bytes). |
| Landing Zone | The designated radial zone of the disk, usually at the inner part of the disk, where the heads are stored to avoid contact with the data cylinders when power to the drive is off. The read/write heads inside a drive move over the spinning platter surfaces, in response to a BIOS Seek command. When they reach the specified cylinder address, they stop and are stationary while reading or writing data to a specific sector address. In response to a command, the heads may move to many different addresses to perform data storage or retrieval tasks. |
| Linear density | Mass per unit length expressed as grams per centimeter, pounds per foot, or equivalent units. It is the quotient obtained by dividing the mass of a fiber or yarn by its length. |
| 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. The very first sector on a hard drive. It contains the codes necessary for the computer to start up. It also contains the partition table, which describes how the hard drive is organized. Also called the Boot Sector. |
| Megabyte (MB) | Expression used to describe storage capacity or amount of data. One megabyte is about one million of bytes/characters (10242). Amount of memory equal to 1,048,576 bytes of information. (Abbreviated MB.) |
| Mirror | In geographic mirroring, an independent disk pool that is being geographically mirrored so that it is a replica of the production copy of the independent disk pool. If a switchover or failover causes the system that owns the mirror copy to become the current primary node, the mirror copy becomes the production copy of the independent disk pool. The mirror copy has current data only when geographic mirroring is active. |
| 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. This refers to the mean time between failures. It is the reliability rating indicating the expected failure rate of a product in power on hours. |
| Multi-media | A simultaneous presentation of data in more than one form, such as sound or picture. Digital representation of different types of information such as text, graphics, audio and video, so that all of these can be stored in a common medium (such as CD-ROM or computer storage). |
| Multi-user | A system that enables more than one user to access the same data at the same time. Multi-user systems consist of two or more computers that are connected together and that share data and peripherals. A multi-user system includes a host computer (file server) and one or more stations. All stations share the same hard disk and may share other devices such as printers. |
| 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. Short for NT File System, one of the file system for the Windows NT operating system (Windows NT also supports the FAT file system). NTFS has features to improve reliability, such as transaction logs to help recover from disk failures. To control access to files, you can set permissions for directories and/or individual files. NTFS files are not accessible from other operating such as DOS. |
| 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. A 64-byte data structure that defines the way a PC's hard disk is divided into logical sectors known as partitions. The partition table describes to the operating system how the hard disk is divided. Each partition on a disk has a corresponding entry in the partition table. The partition table is always stored in the first physical sector of a disk drive. |
| PCB | Printed Circuit Board. Used for the electronics board on the hard drive. Board that contains layers of circuitry that is used to connect components to a system. |
| 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 aluminium, 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. |
| P-List | Primary Defect List. List of defective sectors in a hard drive. The defective sectors may not be used for storing data. The P-List is generated during fabrication. The disk itself stores it internally. |
| Port | A connection or socket on the motherboard or controller card. |
| 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. This stands for Redundant Array of Independent Disks. It is a subsystem storage concept designed for the purpose of offering higher levels of protection from data loss that can occur from any down time caused by malfunctions compared to the protection offered by conventional disk drives. RAID arrays composed of conventional discs can function for hundreds or even thousands of years without losing data because of a disk failure. |
| RAM |
Random Access Memory.
Memory that allows any storage location to be accessed randomly, as opposed to tape drives, which are sequential access devices. Random Access Memory or RAM is a type of computer storage whose contents can be accessed in any order. This is in contrast to sequential memory devices such as magnetic tapes, discs and drums, in which the mechanical movement of the storage medium forces the computer to access data in a fixed order. It is usually implied that RAM can be both written to and read from, in contrast to Read-Only Memory or ROM. Chips in the computer used for temporary storage of data. |
| Raw data | Raw data is uninterpreted 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. Data which has not been processed; may or may not be in machine-compatible form. |
| 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. A small electro-magnet in a drive that skims above the surface of a disk or platter and reads information from, or writes data to, the disk. |
| 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). An abbreviation for Read Only Memory. ROM is used to hold programs and data that must survive when the computer is turned off. Because ROM is non-volatile; data in ROM will remain unchanged the next time the computer is turned back on. As the name implies, data cannot be easily written to ROM; depending on the technology used in the ROM, writing may require special hardware, or may be impossible. A computer's BIOS may be stored in ROM. |
| SATA | Serial ATA is an evolutionary replacement for the Parallel ATA physical storage interface. Often abbreviated SATA or S-ATA, an evolution of the Parallel ATA physical storage interface. Serial ATA is a serial link -- a single cable with a minimum of four wires creates a point-to-point connection between devices. Transfer rates for Serial ATA begin at 150 MBps and SATA II 300MBps. One of the main design advantages of Serial ATA is that the thinner serial cables facilitate more efficient airflow inside a form factor and also allow for smaller chassis designs. |
| SCSI | Small Computer Systems Interface. This acronym is pronounced "scuzzy" and stands for Small Computer Systems Interface. There are two types of interfaces for hard drives, CD-ROM drives, etc. One is SCSI, the other is IDE. IDE is much more common and less expensive. SCSI is more expensive and also more flexible and generally faster. With a single SCSI card you can have 15 or more devices whereas you are only allowed to have 4 devices with an IDE system. The fastest hard drives (and generally CD-ROM drives too) are SCSI-based. |
| Sector | Smallest data unit accessible on disk. Normally 512 bytes. Tracks are divided into sections called sectors and the size of these sections are determining by the formatting. The standard sector stores one user record of data. Many factors, such as system type, the drive encoding method, interface and capabilities of the controller determine how many sectors per track are used. Sector and location refer to the sequence number of the sector around the track when the sector is used an an address component. |
| 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. An error from which a program or an operating system is able to recover, as opposed to a hard error, which causes program or operating system failure, requiring the user to reboot the system. |
| Software | General expression used to describe a collection of instructions enabling a computer to solve one or several tasks. Instructions for a computer, organized into sets called programs. |
| Spindle motor | The motor within a hard drive that rotates the platters. The motor that rotates the spindle and therefore the disks. |
| Stiction | The word is a contraction of Static Friction. It is used when the read/write head sticks to the platters lubricate coating. A term used to explain the amount of force needed to start to move an object.Usually higher than is needed to keep the same object moving at a content rate. |
| Storage medium | Collective description of all types of media used for data storage. Examples: hard disk, floppy disk, MO, streamer tape, DAT, DLT, CD. |
| Strap | See jumper. |
| Stripe set | Collection of disks that together, trough striping, makes up one unit. A vehicle for distributing data over multiple drives. |
| 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. This module provides information about the runtime system, such as the Operating System kind, type and version and whether or not the machine supports multiprocessing. |
| 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. |
| Tera byte(TB) | Expression used to describe data storage capacity or amount of data. One tera byte corresponds to 10244 bytes/characters. A terabyte (derived from the SI prefix tera-) is a unit of information or computer storage equal to one trillion (one long scale billion) bytes. It is commonly abbreviated TB. |
| Time taken to make a copy | It takes about 1 hour to make a copy of a new, healthy drive of 8GB. To copy a damaged disk takes much longer. Copying the data in a file context is also slower than making a plain image copy. |
| 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. |
| Unalignment | See off track. |
| 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. A grouping of one or more related volumes treated as a unit. |
| Water damage | A data storage unit that has been exposed to water and has sustained some damage. A data storage unit that has been exposed to water must be kept wet. |
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