Data Recovery

Ultra SCSI
Provides 20 MB/s transfers over an 8-bit bus or 40 MB/s transfers over a 16-bit Wide SCSI bus. Also known as Fast-20 SCSI, this feature is most commonly found in SCSI-3 drives.

Ultra DMA/33
A high-speed host data transfer feature that transfers data at 33.3 MB per second.

Un-correctable Error
An error that cannot be overcome using Error Detection and Correction.

Unformatted Capacity
The total number of usable bytes on a disk, including the space that is required to record location, boundary definitions, and servo data. (See also formatted capacity.)

Universal Serial Bus (USB)
A serial bus with a bandwidth of 1.5 megabits per second (Mbps) for connecting peripherals to a microcomputer. USB can connect up to 127 peripherals, such as external CD-ROM drives, printers, modems, mice, and keyboards, to the system through a single, general-purpose port. This is accomplished by daisy chaining peripherals together. USB supports hot plugging and multiple data streams.

Unrecoverable Error
A read error that cannot be overcome by an ECC scheme or by rereading the data when host retries are enabled.

Untagged Queuing
The ability of the drive to receive a maximum of one I/O process from each initiator.

Upgrade
In hard drives, the replacement of a hard drive with one offering greatercapacity or performance, or both.

TPI (Tracks per inch)
The number of tracks written within each inch of the disk’s surfaces, used to measure how closely the tracks are packed on a disk surface. Also known as track density.

Tagged Queuing
The ability of the drive to receive multiple I/O processes from each initiator.

Task File
The set of I/O Host Interface Registers used to transfer status, commands, and data between the host and the drive for the EIDE interface.

Thin Client Architecture
A computer system in which data is stored centrally, with only limited storage capacity at the various points of use.

Thin Film
A type of coating deposited on a flat surface through a photolithographic process. Thin film is used on disk platters and read/write heads, as well as on the write element of MR heads.

Thin-Film Inductive Head (TFI)
A head technology that uses a thin-film inductive element to read and write data bits on the magnetic surface of the disk.

Time-to-Capacity
Getting to market first with the next highest capacity hard drive.

Time-to-Market
The time it takes to bring a product from concept to market. Generally first-to-market is the desired time-to-market goal.

Time-to-Quality
The time required to bring a new product to market with the best possible level of quality and reliability.

Time-to-Volume
The time required to begin producing a new product in sufficiently high volume to fill commercial requirements.

Track
A concentric magnetic circle pattern on a disk surface used for storing and reading data.

Track-to-track Seek Time
The time that elapses when the read/write heads move from one track to an adjacent track.

Transfer Rate
The rate at which the hard drive sends and receives data from the controller. Processing, head switches, and seeks are all figured into the transfer rate in order to accurately portray drive performance. The burst mode transfer rate is separate from transfer rate, as it refers only to the transfer of data into RAM.

Translating BIOS
A system BIOS that allows access to EIDE drives larger than 528 MB.

SCA-2
SCA-2 (Single Connector Attach) interface incorporates a grounding contact, blindmate connector, direct plug misalignment tolerance, ESD protection, hot swap capability, and backplane connector options for SCSI devices. SCA-2 is commonly called the 80-pin SCSI connector.

SCSI Configure Automatically (SCAM)
Allows users to attach SCSI devices without worrying about configuration options.

SCSI-1
The Small Computer System Interface (ANSI document X3.131-1986).

SCSI-2
The Small Computer System Interface (ANSI document X3.131-1994).

SCSI-3
The ANSI X3T10 Working Documents (under development).

SCSI device
A host computer adapter, a peripheral controller, or an intelligent peripheral that can be attached to a SCSI bus.

SPC
SCSI Primary Commands.

Small Computer System Interface (SCSI)
An interface between a computer and peripheral controllers. Commonly used in enterprise computing and in Apple Macintosh systems. Usually pronounced as “scuzzy.” The equivalent interface system in most personal computers is Enhanced Integrated Drive Electronics, usually called EIDE.

Sector
A 512-byte packet of data in EIDE and SCSI hard drives. This is the smallest amount of data that can be read or written to the drive from the host interface. On Macintosh and Unix drives, sectors are usually grouped into blocks or logical blocks that function as the smallest data unit permitted. Since these blocks are often defined as a single sector, the terms block and sector are sometimes used interchangeably in this context. (Note: The meaning of the term block in connection with the physical configuration of the disk is different from its meaning at the system level. (See also block and cluster.)

Sector Slipping
A technique used to push-down defective sector sites during a format or reassignment operation to maintain sequential order of the data. Spares are located throughout the disk for this purpose.

Seek
The movement of a set of read/write heads to a desired location. The actuator moves the heads to the cylinder containing the track and sector where the data is stored.

Seek Time
A measure (in milliseconds) of how fast the hard drive can move its read/write heads to a desired location.

Self-Monitoring, Analysis, and Reporting Technology (S.M.A.R.T.)
A technology to assist the user in preventing possible system down time due to hard drive failure by attempting to predict imminent hard drive failure before it occurs.

Sequential Access
The reading or writing of data in a sequential order as opposed to random access. Magnetic tape drives store data in sequential blocks.

Serial Storage Architecture (SAA)
The general name given to a set of standards being developed by an ANSI-approved X3 group. The set of standards defines a new serial interface that provides a flexible addressing scheme.

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

Servo Burst
Provides positioning information to the actuator arm, found at equal intervals on each disk surface (embedded servo) or on an entire surface (dedicated servo).

Single-ended SCSI
The standard electrical interface for SCSI. Single-ended means an interface with one signal and one corresponding ground line for each SCSI signal. Used primarily in applications requiring cable lengths under 19 feet (6 meters).

Slave
The second drive in a dual drive combination.

Soft Error
An error that does not repeat when the same location is re-read.

Soft Sectored
A technique that allows the controller to determine the beginning of a sector by reading the format information from the disk.

Spindle
The center, rod-like axle on which the disks are mounted.

Spindle Motor
The motor that rotates the spindle and ultimately the disks.

Spindle Speed
See RPM.

Spindle Synchronization
A feature that causes SCSI hard drives in multiple-drive systems to rotate to the same address location at the same time.

Storage Capacity
The amount of data that can be stored on a hard drive.

Sub-1000 PC
The series of personal computers being designed for sale at prices at or below $1,000 each.

Subsystem
A secondary or component part of a system, as a hard drive is a subsystem of a personal computer.

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

Synchronous Transmission
Transmission in which the sending and receiving devices operate continuously at the same frequency and are held in a desired phase relationship by a correction device.

System Files
The files needed to run an operating system.

System Integrator
An independent professional who specifies and provides the necessary combinations of hardware and software in response to an end user’s needs.

RLL (Run Length Limited)
An encoding scheme used during write operations to facilitate data readback.

ROM (Read Only Memory)
Integrated circuit memory chip containing programs and data that the computer or host can read but cannot modify. The computer can read instructions out of ROM, but cannot store data in ROM.

RPM (Revolutions per Minute)
Rotational speed of the media (disk), also known as the spindle speed. Hard drives typically spin at one constant speed. The slower the RPM, the higher the mechanical latencies. Disk RPM is a critical component of hard drive performance because it directly impacts the rotational latency.

Radial Path
The straight-line path from the center of the disk to the outer edge of the disk.

Random Access Memory (RAM)
Memory that allows any storage location to be accessed randomly, as opposed to tape drives, which are sequential access devices.

Read Channel
Performs the data encoding and conversions the drive needs to write computer generated information onto a magnetic medium and then read that information back with a high degree of accuracy.

Read Verify
A data accuracy check performed by having the disk read data to the controller, which in turn checks for errors but does not pass the data on to the system.

Read/Write Head
See Head.

Recoverable Error
A read error that the drive can correct by ECC recovery or by re-reading the data.

Redundant Arrays of Independent Disks (RAID)
Groupings of hard drives in a single system to provide greater performance and data integrity.

Rotational Latency
The amount of delay in obtaining information from a disk due to the rotation of the disk. For a disk rotating at 5200 RPM, the average rotational latency is 5.8 milliseconds. See also Mechanical Latency.

MB (Megabyte)
One megabyte as 1,000,000 (one million) bytes.

MFM (Multiple Frequency Modulation)
A method of encoding analog signals into magnetic pulses or bits.

MR Heads (Magneto-resistive Heads)
MR heads were developed to increase area density and improve drive performance. MR heads use separate read and write elements, as opposed to traditional inductive thin-film read-write heads. MR heads use an inductive element for writing data, and a separate magneto-resistive element for reading information. The read element has a magnetically sensitive material that detects data recorded on the magnetic disk surface. MR head construction results in a stronger signal than that produced by inductive thin-film read-write heads, which permits it to read higher area density data. Since the magneto-resistive element can only read data, a conventional thin-film inductive element writes data to the disk.

MTBF (Mean Time Between Failure)
A measure of reliability. The MTBF is the number of failures divided by the number of hours the component has operated. The longer the time span between failures, the more reliable the device.

MTTR (Mean Time to Repair)
The average time it takes to repair a drive in the field. In the field, only major subassemblies are changed (the PCB, sealed housing, etc.), excluding component level repairs as these are not performed in the field.

Magnetic Flux
The pattern of magnetic pole directions of the bits written on the disk.

Manufacturing Yield
The portion of unit production of a manufacturing process that is usable, saleable product; usually expressed as a percent of total output of that product.

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

Media
In hard drives, the disks and their magnetic coatings; sometimes refers to the coating material alone.

Mechanical Latencies
Include both seek time and rotational latency. Mechanical latencies are the main hindrance to higher performance in hard drives. The time delays of mechanical latencies are one hundred times higher than electronic (non-mechanical) latencies associated with the transferring of data. See also Seek Time, Rotational Latency.

Memory
A device or storage system capable of storing and retrieving data.

Millisecond (ms)
1/1,000 (one-thousandth) of a second. Hard disks are rated in milliseconds. Higher numbers mean slower performance.

Multi-media
A simultaneous presentation of data in more than one form, such as by means of both visual and audio.

Multi-user
In information technology, a system that enables more than one user to access data at the same time.