A sector is a logical segment of information on a particular track, and is the smallest addressable unit of
storage on a disk. Tracks are divided into sectors, with each sector 512 bytes long. They
contain data, but also contain information as to where the data is located,
among other useful bits of information. Modern drives use
ZDR - Zone Density Recording, where there are more sectors per track
on the outside of the disk where there is more surface area, and fewer and fewer sectors
as you go in toward the center of the drive. Newer drives have about 16 zones now. This
allows more data to fit on the drive. The outer zones therefore have a higher data transfer
rate that those closer to the center of the drive.
SECONDARY (IDE) PORT
A "secondary" IDE port or interface is virtually identical to a "primary" IDE
port or interface except it uses a different interrupt and I/O address to avoid
collisions with the primary interface. A secondary interface allows you to connect another ribbon
cable with two additional ATA devices (hard disk, ATAPI CD-ROM or ATAPI tape) for a total of four.
SECTOR ADDRESS TRANSLATION
Most drives manufactured within the last 3 years feature a universal translate
mode. In an AT/EISA-class system, the drive may be configured to any specified combination
of cylinders, heads and sectors within the range of the drive's formatted
SECTOR PULSE SIGNAL
A digital signal pulse which indicates the beginning of a sector. Embedded servo pattern or
other prerecorded information may be present on the disk when sector is active. Only present
in hard sectored drives.
A random access operation by the disk drive. The act of moving a set of read/write heads
so that one of them is over the desired cylinder. The actuator or positioner moves the
heads to the cylinder containing the desired track and sector.
SEEK COMPLETE SIGNAL
A digital signal level which indicates that the positioner is not moving and is located
over a cylinder or offset position.
The elapsed time between the issuing of a step pulse or seek command and when the head
settles onto the desired cylinder. This is sometimes is measured without settling
times, or the time necessary for the head to settle over the specified cylinder.
The writing or reading of data in a sequential order such as reading data blocks stored one
after the other on magnetic tape. This is contrasted to random access of information.
A momentary servo pattern used in embedded servo control implementations usually positioned
between sectors or at the end of a track.
A technique by which the speed or position of a moving device is forced into conformity
with a desired or standard speed or position.
A magnetic head designed for accurately reading (only) of servo information.
A read-back signal that indicates the position of a head relative to a track.
A recording surface in a multi-surface disk drive that only contains control information
which provides timing, head position, and track-following information for the data surfaces.
An automatic system for maintaining the read/write head on track; can be either
"open loop", "quasi-closed loop", or "closed loop".
A track on a servo surface. The prerecorded reference track on the dedicated servo surface
of a disk drive. All data track positions are compared to their corresponding servo track
to determine "off track"/"on track" position.
The time it takes a head to stop vibrating, within specified limits, after it reaches the desired cylinder.
Semiconductor material generally used to manufacture microprocessors and other integrated circuit chips.
SMALL COMPUTER SYSTEM INTERFACE (SCSI)
An intelligent interface that incorporates controller functions directly into the drive. See
the SCSI vs. IDE.
Self-Monitoring Analysis and Reporting Technology.
Prediction of device degradation and/or faults.
A data error which can be overcome by rereading the data or repositioning the head.
A technique where the controller determines the beginning of a sector by the reading of
format information from the disk. This is contrasted to hard sectoring where a digital
signal indicates the beginning of a sector on a track.
Applications programs, operating systems, and other programs as opposed to
The rotating hub structure to which the disks are attached.
The motor that rotates the spindle and therefore the disks.
Magnetic disk or tape that has the magnetic layer deposited by sputtering means.
This indicates the minimum cycles for reliable start/stop function at a 60% confidence level.
A motor that has known detent positions where the rotor will stop with the proper control
in some cases. The digitally controlled motor moves the head positioner from track to track
in small, step-like motions.
The amount of data that can be stored in a memory location, or on a disk drive. Usually
specified in kilobytes for main memory and floppy drives and
megabytes & gigabytes for mass
storage devices. See Decimal vs. Digital for further details.
Usually refers to recording density (BPI,
TPI, or a combination of both.)
A memory location, identified by an address where information may be read or written.
STROBE OFFSET SIGNAL
A group of digital input signal levels which cause the read PLL and/or data decoder to
shift the decoding windows by fractional amounts. Often early/late are modified when two
signals are used.
A letters and/or numbers at the end of a model number of many hard drives. Many
times this denotes the type of drive
and the number of surfaces & heads.
Each platter (disk) has two surfaces, the top and bottom surface.
Each surface has it's own head for reading, writing & erasing data.