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Computer Hard Drive Glossary

In this computer hardware glossary, we list all of the different terms used in describing hard drives and define all the major components and functions of a hard drive.

ATA - ATA stands for Advanced Technology Attachment, and was developed by Western Digital in 1986.

ATAPI - ATAPI or Parallel ATA refers to improvements made to ATA drives in 1998.

BIOS - Basic Input/Output System, is the software that runs a computer's motherboard and coordinates between devices.

Bit - Bits are 1 Binary Unit of Memory and represent states in memory.

Blocks - Hard Drive blocks are a sector or multiple sectors depending on the partitioning system. A block is the smallest amount of addressable data so every file on the system can at a minimum occupy one block. Advanced systems can place data smaller than the size of one block together to optimize storage.

Buffer - A hard drive buffer is a small amount of temporary memory used when writing to the disk to prevent errors if data is interrupted.

Cable Select - Cable select is a mode of ATA/IDE disks that allows the disk to try to figure out whether it is a master or slave on the bus.

Cache - A cache is a small amount of fast memory where information that has recently been accessed is stored. If the information is requested again the drive can return this information without accessing the disk, which is faster.

Cylinders - Cylinders are a range of tracks on a platter that can be accessed without moving the actuator.

Daisy Chain - Daisy chaining refers to attaching drives in sequence that then act as one cable or bus.

Defragmentation - Fragmentation occurs when several blocks hold less than their capacity of data. Defragmentation involves placing data together to fill blocks, and save space. It also involves placing similar data together.

EIDE - Enhanced IDE is a series of enhancements to IDE that came out in 1994, around the time of ATA-2.

Enclosure - Enclosure refers to the device into which an external hard drive is place.

EPROM - Erasable Programmable Read Only Memory acts as read only non-modifiable memory but can be changed if need be. It is often where the software that tells the drive how to function is located.

External - Refers to hard disks that are placed in enclosures outside of a computer.

FAT - FAT refers to the original Microsoft File Allocation Table, the file system for Windows 3.1.

FAT 32 - FAT 32 was an upgrade to the FAT file system introduced with Windows 95 to allow 32 bit addressing in the Windows file system.

FireWire - FireWire is one implementation of the IEEE 1394 Interface and also the original technology used for syncing iPods, as well as allowing them to serve as external hard drives. It is still used for high performance hard drives.

Flash ROM - Flash ROM is a type of memory which is static, unchangeable, but can be overwritten to function differently. This is often used to store hard drive drivers, or boot information.

Head - The head is the part of a hard drive that reads what is stored on the disk.

HFS - HFS, or Hierarchal file system, replaced the original Macintosh file system in 1985. It did not see major changes for decades, when HFS plus was introduced.

HFS+ - HFS Plus replaced the original HFS file system enabling 32 bit addressing and Unicode support. It is the default file system on the iPod.

Hot Swapping - is the ability to remove a drive and either reattach it or another drive while the system it is attached to is still running without causing the system to need to restart, or generating errors.

i.Link - i.Link is a Sony implementation of the IEEE 1394 drive interface standard. Unlike other implementations i.Link does not provide power for attached devices.

IDE - Integrated Drive Electronics is the name for the interface, developed by Western Digital, which accompanied ATA.

IEEE 1394 - IEEE 1394 is a high speed drive connection which widely replaced SCSI drives. It was invented by Apple, Inc, and Sony.

Internal - Internal drives reside inside the computer attached to the logic or mother board directly.

Journaling - Journaling is when a file system writes changes to a temporary file before making them. As a result these systems reboot faster after crashes, and are less prone to file corruption.

Jump Drive - Jump Drive is a synonym for a generic USB Flash Memory drive, typically these are the size of a keychain but can hold up to several gigabytes of data and are extremely portable.

Master - Master drives are the first drive on the bus, though they can be physically located anywhere on the cable. Cable select mode made master slave configuring unnecessary.

NAT - Network Attached Storage refers to drives which are attached to the network (either physically or over WiFi) but mount as though they are regular attached drives or network drives.

NTFS - NTFS was a file system introduced with Windows NT, and took its name from NT, which meant New Technology at the time. NTFS supports 32-bit addressing, and journaling, more support for meta-tags.

Partitioned Capacity - Partitioned capacity refers to the actual amount of data a drive can store once it has been partitioned with a given file system.

Partition - A partition on a drive appears as one individual drive on the system it is attached to.

Partition Size - The partition size refers to the size of blocks on a partitioned system. A common partition size is 4k which means the smallest space data can occupy on the disk is 4 kilobytes; thus a 2k file would still take up 4 k.

Platters - Platters are the individual disk inside a hard drive. Typically a hard drive contains several platters.

RAID - A RAID is a Redundant Array of Independent Disk. Data on one disk is automatically duplicated on one or more of the other disks. This makes it easy to switch to a backup disk in the event one fails with little or no interruption to disk function.

RAM Disk - A RAM disk is when a portion of RAM memory is treated as though it were a hard disk. This makes for rapid access however it must be backed up when the computer is shutdown and can be lost in the event of a crash or restart since it does not actually reside on a hard disk until it is saved.

RPMs - Revolutions Per Minute refers to how fast the hard drive can spin while accessing data.

SATA - Serial ATA is an improved ATA interface that appeared in 2003, it replaced the standard IDE cabling with a smaller interface with fewer pins, but with much fast access times.

SCSI - SCSI, or Small Computer System Interface, was developed in 1982. It was extremely fast, enabled external bootable drives, as well as the ability for internal disks to be accessed as though they were external disks on a separate system.

Sector - A sector on a hard drive is one portion of a track within a cylinder.

Seek Time - Seek time is how long a hard drive takes to locate individual data on a disk.

Serial SCSI - Serial attached SCSI is a high-speed update to SCSI technology that is also compatible with SATA drives.

Shadow RAM - Shadow RAM allows video memory to be temporarily taken out of main memory to free up that memory for other operations.

Slave - Slav drives must communicate through another drive, the master drive, on the bus.

Solid State - Solid-state drives are essentially a large number of RAM chips that act as a permanent hard drive. They are significantly faster than traditional hard drives and break less often as they have no moving parts.

Spindle - The spindle is the device that spins the hard disk platters, and hold the arms which read data from the various platters.

UFS - UFS is the UNIX File System and is used by UNIX, Linux, and can be used by a variety o other file systems.

Ultra DMA - Ultra DMA or UDMA is an improvement for ATA drives which enabled ATA to hit transfer speeds of 33.3 megabytes per second.

Write Cache - A write cache is a high performance memory chip where data to be written is stored while the drive is being written to to ensure there are not slow downs in writing which may cause the write operation to fail.

ZFS - ZFS is a special type of file system, developed by Sun Microsystems, which also enables incremental backups at the file system level. Few systems can boot using ZFS drives and they are most popular as network attached storage drives.

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