旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴커 � Hard Disk Tech Specs(tm) v3.0 � 읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸 Hard Drive Solutions Family(tm)  Drive Type: On AT class machines, the system BIOS has a built-in drive table indexed by a drive type. For example, a common Phoenix BIOS used in many 286-class machines recognizes that drive type 44 has 820 cylinders, 6 heads, and 17 sectors per track. ESDI: Enhanced Small Device Interface. This interface is an enhanced version of the ST-506 interface, capable of transfer rates as high as 24 Mbits/sec. Error checking and correction is significantly improved over the ST-506 interface. In addition, ESDI controllers are capable of handling floppy drives, tape backup drives, and direct file transfers for any of these storage devices. Form Factor: The physical width dimension of the hard drive. Typically, 5.25, 3.50, or 8.00 inch. Head: The element that actually reads or writes data to the disk surface. Hard drives usually have two or more heads that are stepped from track to track in unison by a head actuator (stepper motor, voice coil, or electronic). Currently, there are three types of heads: - Monolithic ( 8,000 BPI) - Composite (12,000 BPI) - Thin Film (25,000 BPI) IDE: Integrated Drive Electronics. IDE drives have a built- in controller, and only need a gateway interface to the I/O bus on the main system board. Therefore, all command interpretation is done by the electronics on the drive. Gigabyte: 1,073,741,824 bytes. Low-Level Format: * see "Format." Master: The primary drive. "Slave" is used to refer to the secondary drive. Typically used to describe the relationship between two IDE hard drives. Megabyte: 1,048,576 bytes. The standard method for expressing the capacity of a hard drive. MFM: Modified Frequency Modulation. A fixed-length encoding method used by many hard drives. All bits are evenly spaced, with error-correction information stored with the data. MTBF: Mean Time Before Failure. This is the average amount of time, usually expressed in thousands of hours, that the drive will operate before requiring repair or replacement. MZR: Multiple-Zone Recording. This is a method of media optimization where zones of neighboring tracks are given progressively more sectors per track as the zones move toward the outside of the platter. For example, a drive that has 612 cylinders and employs an MZR 3-zone scheme might group 304 tracks in each zone, with the innermost zone having less sectors per track than the middle zone, and with the outer- most zone having more sectors per track than the middle zone. RWC: Reduced Write Current. Expressed as the cylinder from which point the current used to write to the disk surface is reduced in order to maintain the separate identity of bits in a sector. This is sometimes necessary to compensate for the smaller sectors found on the inner tracks. RLL: Run Length Limited. An encoding method used to limit the length of data written in order to increase the capacity of the drive. In RLL2,7, the run length of 0's may be no longer than seven. Most drives designed for use with MFM controllers can be used with RLL controllers, resulting in a significant gain in storage capacity (this is against the manufacturer's suggestion). SASI: Shugart Associates Systems Interface. Pioneered by Al Shugart, this interface is the predecessor to the SCSI interface. SCSI: Small Computer System Interface. An interface that allows up to seven intelligent devices to be attached to the system's bus. Currently, hard drives, tape backup units, and printers are the predominant SCSI devices available. SCSI-Mac: Small Computer System Interface - Macintosh Sector: A logical section of a track. Most drives pack 512 bytes into a sector. Seek Time: The average seek time, expressed in milliseconds, indicates the average time necessary for the read/ write heads to find or seek to a specified cylinder. Another rating is track-to-track seek time. This is the time necessary to seek from one track to an adjacent track, also expressed in milliseconds. Slave: * see "Master." ST-506/412: An interface developed by Shugart in 1980 for use with their ST-506 drive (5 Mb). In 1981, a buffered seek was added to handle their new ST-412 drive (10 Mb). A typical ST-506/412 interface is capable of transfer rates of 5 Mbits/sec. Stepper Motor: The motor that steps the read/write heads from track to track. The shaft of the stepper motor rotates in fixed degrees, allowing accurate head positioning. * see also "Voice-Coil Actuator." SMD: Storage Module Drive. An interface used primarily on high-capacity drives. Voice-Coil Actuator: A solenoid used to control the positioning of the read-write heads. Instead of stepping to the appropriate track, as is the case with a stepper motor, the voice-coil actuator can seek directly to the desired track using servo information. * see also "Stepper Motor." Winchester Drive: IBM originally made a drive for mainframes that had 30 MB of fixed media, and 30 MB of removable media. The Winchester gun factory makes a rifle with a 30-30 calibre, thus the name. Write Precomp: Write Precompensation. The gradual reduction in write current from the outermost to innermost tracks. This occurs over the entire range of cylinders, as opposed to RWC which starts at a pre-defined cylinder. ZBR: Zone-Bit Recording. Developed by Seagate, this is a type of media optimization that varies the number of sectors per track. The outer tracks have more sectors than the inner tracks.