Glossary

AI-1

Appendix I

GLOSSARY ABRASIVITY—The ability of the magnetic tape to wear the head. ADDITIVE—Any material in the coating of magnetic tape other than the oxide and binder resins. (Examples: plasticizers (to soften an otherwise hard or brittle binder), lubricants (to lower the coefficient of friction of an otherwise high-friction binder), fungicides (to prevent fungus growth), dispersants (to uniformly distribute the oxide particles), and dyes.) ALTERNATING CURRENT (ac) BIAS—(1) The alternating current, usually of a frequency several times higher than the highest input signal frequency, that is fed to a record head in addition to the input signal current. (2) Linearizes the recording process. (3) Is universally used in direct analog recording.

AMPLITUDE/FREQUENCY RESPONSE—(See frequency response.) ANALOG RECORDING—A method of recording in which some characteristic of the record current, such as amplitude or frequency, is continuously varied in a manner similar to the variations of the original signal. AZIMUTH ALIGNMENT—The alignment of the recording and reproducing gaps so their center lines lie parallel with one another. Misalignment of the gaps causes a loss in output at short wavelengths. BACKINGS—(See base film.) BANDWIDTH—The frequency within which the performance of a recorder with respect to some characteristic (usually frequency response) falls within specified limits, or within which some performance characteristic (such as noise) is measured.

BASE FILM—The plastic substrate material used in magnetic tape that supports the coating. BER—(See bit error rate.) BIAS-INDUCED NOISE (See noise.) BINARY—(1) Two values ("O" or "1") or states (ON or OFF). (2) The number systems used in computers. BINDER—A compound consisting of organic resins used to bond the oxide particles to the base material, the actual composition being considered proprietary information by each magnetic tape manufacturer. The binder is required to be flexible but still maintain the ability to resist flaking or shedding during extended wear passes.

BIT—(1) The acronym binary digit. (2) The smallest unit of data, either "O" or "1". (3) One recorded information cell, as applied in magnetic recording. AI-2 BIT DENSITY—(See packing density.) bit error rate (BER).—(1) The number of errors a specific magnetic tape may contain, as used in high-density recording. (2) Is expressed in errors per data bit, such as 1 in 106, or one error in one million data bits. BREAK ELONGATION—The relative elongation of a specimen of magnetic tape of base film at the instant of breaking when it has been stretched at a given rate.

BROWN STAIN—(1) A thin discoloration of the head's top surface, usually a chemical reaction between the head's surface materials and the tape binder, the tape lubricant, or the head's bonding materials. (2) Its origin is not well understood, but is known to occur in low humidity. BUCKLING—(1) A deformation of the circular form of a tape pack. (2) Caused perhaps by a combination of improper winding tension, adverse storage conditions, and/or poor reel hub configuration. BUILD-UP—(1) A snowballing effect started by debris and tape magnetic particles embedded in the contamination. (2) The thickness of this build-up can cause an intense in head-to-tape separation, as well as an increase in the coefficient of friction. (3) Solvent cleaning of the head's top surface will usually remove the build-up.

BULK-ERASED NOISE—See noise. BULK ERASER (DEGAUSSER)—An equipment for erasing a full reel of previously recorded signals on tape. BYTE—A group of bits (next to each other) that are considered a unit (example, an 8-bit byte). CERTIFIED TAPE—A tape that is electrically tested on a specified number of tracks and is certified by the supplier to have less than a certain total number of permanent errors. CERTIFIER—(1) An equipment that tests the ability of magnetic tape to record and reproduce. (2) Counts and charts each error on the tape, including the level and duration of dropouts.

(3) In the certify mode, stops the tape at an error to allow for visual inspection of the tape to see if the cause of the error is correctable or permanent. CHICKEN TRACKS—(1) A line of small craters in the head's top surface running in the direction of tape motion. (2) Usually caused by a loose, small, hard particle moving with the tape over the head. CINCHING—(1) The tape folds resulting from longitudinal slippage between the layers of tape in a tape pack. (2) Caused by uneven tension when the roll is accelerated or decelerated.

CLEAN ROOMS—The rooms of which their cleanliness is measured by the number of particles of a given size per cubic foot of room volume. (Examples (1) A class 100,000 clean room may have no more than 100,000 particles 0.5 fm or larger per cubic foot, and so on for class 10,000 and class 100 rooms. (2) A class 10,000 room may have no more than 65 5-fm particles per cubic foot, while class 100,000 may have no more than 700 5-fm particles per cubit foot.) CLEANER—(See winder/cleaner.) COATING—The magnetic layer of a magnetic tape consisting of oxide particles held in a binder that is applied to the base film.

AI-3 COATING RESISTANCE—(1) The electrical resistance of the coating measured between two parallel electrodes spaced a known distance apart along the length of the tape. (2) Called resistivity on specification sheets. COATING THICKNESS—The thickness of the magnetic coating applied to the base film. COATING-TO-BACKING ADHESION—(See anchorage.) CONTAMINATION—(1) A thick, tacky (viscous) deposit on the head's top surface, which causes a large increase in the effective head-to-tape coefficient of friction. (2) May not be removable by solvent cleaning.

CORE MATERIAL—(1) hard core material.—(a) Hard metal laminations bonded together to form the core, with a typical thickness of 0.005 to 0.004 inch. (Hard metal wears much more slowly than soft laminations.) (b) Hard solid metal, such as alphenol or sendust. (Wear rates are much lower than those of soft metal laminations.) (2) soft core material.—(a) Soft metal laminations bonded together to form the core, with a typical thickness of 0.0005 to 0.004 inch. (b) Usually, a high nickel/iron alloy, such as Hy Mu 800. (c) These materials have a relatively poor wear rate.

CRACK—A narrow, deep break in the head's surface material. CREEP—The time-dependent strain at a constant stress (tape deformation). CROSSFEED—See crosstalk and write feedthrough. CROSSPLAY—The ability to interchange recordings between recorders while maintaining a given level of performance. CROSSTALK—(1) The magnetic coupling from one track to another in the tape's read/write head. (2) See also write feedthrough. CUPPING—(1) The curvature of a magnetic tape pack in the lateral direction. (2) May be caused by differences between the coefficients of thermal or hygroscopic expansion of coating and base film.

db—See decibel. dc NOISE—(See noise.) DECIBEL (db)—A dimensionless unit for expressing the ratio of two powers or voltages or currents on a logarithmic scale. If A and B represent two voltages or currents, the ratio A/B corresponds to 20 log A/B decibels. One decibel represents a ratio of approximately 1.1 to 1 between A and B. Other values are as follows: AI-4

Ratio Decibel

10 1.4 3 26 41 2 10 20 100 40 1000 60 DEFECT—(1) An imperfection in the tape leading to a variation in output or a dropout. (2) The most common defects are surface projections of oxide agglomerates, embedded foreign matter, and redeposited wear products. DEGAUSSER—See bulk eraser. DELAY MODULATION—(See modified frequency modulation.) DIGITAL RECORDING—(1) A method of recording in which the information is first coded in a digital form. (2) Usually, a binary code is used, with recording taking place in two discrete values/polarities of residual flux.

DIRECT RECORDING—An analog recording that records and reproduces data in the electrical form of its source. DISK—(1) A disk-drive storage device on which information is magnetically recorded and retrieved. (2) Can be either hard (rigid) or floppy (flexible). DISK DRIVE—A storage device for recording and retrieving data on hard or floppy disks. DISK PACK—A portable, interchangeable device that contains more than one hard-disk platter and is used in hard-disk drives. DISPERSION—The distribution of the oxide particles within a tape's binder.

DISTORTION—(see harmonic distortion.). DRAG—The fractional tension differential across the contact area caused when the tape contacts some element in the tape path (such as the head, tape guides, tape bearings, or column walls). DROPOUT—(1) A temporary reduction in the output of a magnetic tape of more than a certain predetermined amount. (2) Expressed in terms of the percentage reduction or decibel loss. DROPOUT COUNT—The number of dropouts detected in a given length of magnetic tape. DURABILITY—The number of passes that can be made before a significant degradation of output occurs, divided by the corresponding number that can be made using a reference tape.

DYNAMIC—(See tape skew.) DYNAMIC RANGE—(1) The bandwidth within which a satisfactory signal-to-noise ratio is obtained. (2) See also resolution. AI-5 DYNAMIC SKEW—The change in skew caused by tape motion. DYNAMIC TAPE SKEW—(See tape skew.) EQUIPMENT NOISE—(See noise.) ERASURE—A process by which a signal recorded on a tape is removed and the tape made ready for rerecording. May be accomplished in two ways. (1) In ac erasure, the tape is demagnetized by an alternating magnetic field that is reduced in amplitude from an initially high value. May be accomplished by passing the tape over an erase head fed with high- frequency ac, or by placing the whole roll of tape in a decreasing ac field (bulk erasure).

(2) In dc erasure, the tape is saturated by applying a primarily unidirectional field. May be accomplished by passing the tape over a head fed with dc or over a permanent magnet. Additional stages may be included in dc erasure to leave the tape in a more nearly unmagnetized condition. FERRITE—A powdered and compressed ferric-oxide material that has both magnetic properties and light resistance to current flow. FLOPPY DISK—(See disk.) FLUTTER—(See wow.) FLUX—A term, with reference to electrical or electromagnetic devices, that designates collectively all the electric or magnetic lines of force in a region.

FLUX DENSITY—The number of magnetic lines of force passing through a given area. FM—(See frequency modulation.) FREQUENCY MODULATION (FM)—(1) A flux reversal at the beginning of a cell time represents a clock bit. (2) A "1" bit is a flux reversal at the center of the cell time. (3) A "0" bit is an absence of a flux reversal. FREQUENCY RESPONSE—(1) The variation of sensitivity with signal frequency. (2) The frequency response of a tape is usually given in decibels relative to a referenced frequency- output level. (3) Also called amplitude/frequency response.

GAMMA-FERRIC OXIDE—The common magnetic constituent of magnetic tapes in a dispersion of fine, needle-like particles within the coating. GAP EROSION—(1) The read or write gap increased in length and retreated below the head surface. (2) Usually due to deterioration of core material at the edges of the gap. GAP LOSS—(1) The loss in output due to the finite gap length of the reproduce head. (2) The loss increases as the wavelength decreases. GAP WIDTH—The dimension of the gap of a magnetic head measured in the direction perpendicular to the direction of the tape path.

GAUSS—The metric unit of the magnetic flux density equal to 1 Mx/CM 2. HARD DISK—(See disk.) AI-6 HARD FERRITE—A ferrite with a very low wear rate when compared with the soft metal laminations. HARD METAL LAMINATIONS—(See core material, hard.) HARD SOLID METAL—(see core material, hard.) HARMONIC DISTORTION—A signal non-linearity with harmonics of the fundamental in the output when the input signal is sinusoidal. HEAD CONTAMINATION—(See tape-to-head separation.) HEAD CONTOUR—(1) The complex shape of the contacting surface of a head as a result of manufacture, head lapping, or wear. (2) The contour of a head is always changing throughout the head's life and, in many cases, is responsible for retiring the head.

HEAD CRASH—A term used for the damage to a hard disk caused by the physical contact made between the magnetic read/write heads and the surface of the hard-disk platter. HEAD STICK—(1) A common word for a large increase in head-to-tape friction caused by (a) a stick by-product exuded by conditions due to tape age, temperature/humidity, and head-to- tape pressure, and (b) very smooth tapes coupled with large area heads. (2) See also sticktion and stick-slip. HEAD-TO-TAPE CONTACT—The degree that a tape's magnetic coating approaches the surface of the record or reproduce head during normal operation.

INTERLAYER TRANSFER—Any loose material, such as oxide, generated by tape wear or a head-stick condition which is transferred from the oxide to the back of the tape, or from the back side to the oxide when the tape is wound on a reel. INTERMODULATION DISTORTION—(1) A signal non-linearity with frequencies in the output equal to sums and differences of integral multiples of the component frequencies present in the input signal. (2) Harmonies are usually not included as part of the intermodulation distortion. INTERSYMBOL INTERFERENCE—(1) An interference resulting in a phase shift of the cell playback crossover point with respect to the data clock. (2) When a recording system has limited record resolution, a flux transition being recorded will extend beyond its cell boundaries, adding or subtracting from the flux in the adjacent bit cells of symbols.

IRON OXIDE—(See gamma-ferric oxide.) LAMINATIONS—(see core material.) LATERAL DIRECTION—The direction across the width of the tape. LAYER-TO-LAYER ADHESION—The tendency for adjacent layers of tape in a roll to adhere to one another. LAYER-TO-LAYER TRANSFER—The magnetization of a layer of tape in a roll by the field from a nearby recorded layer, sometimes referred to as print through. LBE—(See lower band edge.) AI-7 LINEARITY—The extent to which the magnitude of the reproduced output is directly proportional to the magnitude of the signal applied to the input of the recorder.

LONG-TERM TAPE SPEED—(See tape speed.) LONGITUDINAL CURVATURE—Any deviation from the straightness of a length of tape. LOOSE DEBRIS—Any material that is very lightly bonded to the tape or the head's top surface, removable by tape motion. LOWER BAND EDGE (LBE)—The lower band edge of the recorder/reproducer response (usually at the -3-dB point). LUBRICANT—(See additive.) MAGNETIC INSTABILITY—(1) The property of a magnetic material that causes variations in the residual flux density of a tape to occur with temperature, time, and/or mechanical flexing. (2) A function of particle size, magnetizing field strength, and anisotropy.

MAGNETIC MEDIA—A base film, coated with magnetic particles held in a binder. (The magnetic particles are usually needle-like, single-domain, gamma-ferric oxide.) MAGNETIZING FIELD STRENGTH—The instantaneous strength of the magnetic field applied to a sample of magnetic material. MFM—(See modified frequency modulation.) MODIFIED FREQUENCY MODULATION (MFM)—(1) A code that has a "1" and a "O" corresponding to the respective presence or absence of a transition in the center of the corresponding bit cell. (2) Additional transitions at the cell boundaries occur only between bit cells that contain consecutive "0" values. (3) Also called delay modulation.

MODULATION NOISE—(See noise.) NOISE—Any unwanted electrical disturbances other than crosstalk or distortion components that occur at the output of the reproduce amplifier. (1) System noise is the total noise produced by the whole recording system, including the tape. (2) Equipment noise is produced by all the components of the system, with the exception of the tape. (3) Tape noise can be specifically ascribed to the tape. The following are typical sources of tape noise: (a) Bulk- erased noise arises when a bulk-erased tape with the erase and record heads completely deenergized is reproduced. (b) Zero-modulation noise arises when an erased tape with the erase and record heads energized as they would be in normal operation, but with zero input signal, is reproduced. This noise is usually 3 to 4 dB higher than the bulk-erased noise. The difference between bulk-erased and zero-modulation noise is sometimes termed bias-induced noise. (c) Saturation noise arises when a uniformly saturated tape is reproduced. This is often some 15 dB higher than the bulk-erased noise and is associated with imperfect particle dispersion. (d) Dc noise arises when a tape that has been non-uniformly magnetized by energizing the record head with dc, either in the presence or the absence of bias, is reproduced. This noise has pronounced, long, wavelength components that can be as much as 20 dB higher than those obtained from a bulk-erased tape. At very high values of dc, the dc noise approaches the saturation noise. Dc noise is actually the low-frequency component of modulation noise. (e) Modulation noise is essentially a modulation of the desired signal by noise that is caused by non-uniform dispersion of elementary magnetic particles in the AI-8 tape’ s coating material. This noise, which occurs only when a recorded tape is reproduced, increases with the intensity of the reproduced signal. Dc noise is actually the low-frequency component of modulation noise.

NOISE PULSE—(1) A short-duration false signal occurring during the reproduction of a tape. (2) A signal that is of a magnitude considerably in excess of the average peak value of the ordinary system noise. NOMINAL BIT TIME—(1) The average bit time of recording at continuous maximum-flux reversals. (2) Also called cell time. NON-RETURN-TO-ZERO (NRZ0)—The flux reversal for a "0"; no flux reversal for a "1." NON-RETURN-TO-ZERO INVERTED (NRZI)—The flux reversal for a "1"; no flux reversal for a "0." NON-RETURN-TO-ZERO (NRZ) RECORDING—(See digital recording.) OERSTED—A unit of magnetic field strength.

OUTPUT—The magnitude of the reproduced signal voltage, usually measured at the output of the reproduced amplifier. OXIDE BUILD-UP—The accumulation of oxide or wear products as deposits on the surface of heads and guides. OXIDE LOADING—(1) A measure of the density with which oxide is packed into a coating. (2) The weight of the oxide per unit volume of the coating. OXIDE SHED—The loosening of particles of oxide from the tape coating during use. PACKING DENSITY—The amount of digital information recorded along the length of a tape, measured in bits per inch.

PARTICLE ORIENTATION—The rotation of needle-like particles so that their longest dimensions tend to lie parallel to one another. PARTICLE SHAPE—The needle-like particles of gamma-ferric oxide used in conventional magnetic tape, with a dimensional ratio of about 6 to 1. PARTICLE SIZE—The physical dimensions of magnetic particles used in a magnetic tape. PERMANENT ELONGATION—The percentage of elongation remaining on a tape or a length of base film after a given load applied for a given time has been removed. PLASTICIZER—(See additive.) POLYESER—(1) An acronym for polyethylene glycol terephthalate. (2) The material most commonly used as a base film for precision magnetic tape.

READ/WRITE ERASE HEAD—A three-gap head (read, write, erase) on one body. Sometimes the erase head is bolted to the read/write head. READ/WRITE HEAD—A two-gap head (read, write) on one body. AI-9 REEL—The metal-, glass-, or plastic-flanged hub on which magnetic tape is wound. REFERENCE TAPE—A tape used as a reference against which the performances of other tapes are compared. REMANENCE—(1) The magnetic flux density that remains in a magnetic circuit after removal of applied magnetomotive force. (2) Is not necessarily equal to residual flux density.

REMOVABLE FIXED DISK—A hard-disk device (usually) with only one hard-disk platter that's used to record and retrieve data. RESISTIVITY—(See coating resistance.) RESOLUTION (DYNAMIC RANGE)—The average peak-to-peak signal amplitude at the maximum flux reversal divided by the average peak-to-peak signal amplitude at the minimum flux reversal at the desired recording method. RETENTIVITY—The maximum value of residual flux density corresponding to saturation flux density. RZ RECORDING—(See digital recording.) SATURATION FLUX DENSITY—(1) The maximum intrinsic flux density possible in a sample of magnetic material. (2) The intrinsic flux density asymptotically approaches the saturation flux density as the magnetizing field strength increases.

SATURATION NOISE—(See noise.) SCRATCH—A long, narrow, straight defect in the top surface of a head track or a tape. SENSITIVITY—The magnitude of the output when reproducing a tape recorded with a signal of given magnitude and frequency. SEPARATION LOSS—The loss in output that occurs when the surface of the coating of a magnetic tape fails to make perfect contact with the surface of the record or reproduce head. SHEDDING—The loss of oxide or other particles from the coating or backing of a tape, usually causing contamination of the tape transport and, by redeposit, of the tape itself.

SHORT-TERM TAPE SPEED—(See tape speed.) SIGNAL-TO-NOISE RATIO—(1) The ratio of the power output of a given signal to the noise power in a given bandwidth. (2) Is usually measured by the corresponding root mean square signal and noise voltages appearing across a constant output resistance. SKEW—A deviation of a line connecting the average displacement of the read or write track gaps from a line perpendicular to the reference edge of the tape in the direction of tape motion. SKEW TAPE—(1) The continuous strings of "1" values written on a properly adjusted tape drive for the entire recoverable length of the tape. (2) An "all '1' pattern" on all tracks.

(3) The write head, the write delays, and the tape drive adjusted to write with minimum physical skew and gap scatter. AI-10 SOFT METAL LAMINATIONS—(See core material, soft.) SPOKING—A buckling in which the tape pack is deformed into a shape that approximates a polygon. SPOOL—(See reel.) SQUEAL—(See stick-slip.) STANDARD REFERENCE TAPE—A tape intended for daily calibration, the performance of which has been calibrated to the amplitude reference tape. STATIC—(See tape skew.) STICK-SLIP—(1) A low-speed phenomenon. (2) A relationship between tension, temperature, humidity, wrap angle, head material, tape binder, and elastic properties. (3) When detected audibly, it is a squeal.

STICKTION—The tape's adhering to transport components, such as heads or guides. STIFFNESS—(1) The resistance to bending the tape. (2) A function of tape thickness. (3) A modulus of elasticity. SURFACE TREATMENT—Any process by which the surface smoothness of the tape coating is improved after it has been applied to the base film. SYSTEM NOISE—(See noise.) TAPE CONTAMINATION—(See tape-to-head separation.) TAPE NOISE—(See noise.) TAPE PACK—The form taken by the tape wound on a reel. TAPE SKEW—(1) The tape's deviation from following a linear path when transported across the heads. (2) The terms static and dynamic distinguish between the physically fixed components and the fluctuating components of total tape skew.

TAPE SPEED—(1) The speed at which the tape is transported across the read/write head during normal recording or reproduction. (2) Long-term speed is averaged over a minimum of 15 inches of tape (in inches per second). (3) Short-term speed is the instantaneous (dynamic) tape speed (in inches per second). TAPE-TO-HEAD SEPARATION—(1) Separation.—The separation between a magnetic head and the magnetic tape caused by the (a) foil-bearing effect, (b) improper head contour, which generates standing waves in the tape, and (c) surface roughness of the tape. These conditions are interrelated and are greatly influenced by tape tension and tape compliancy. In a properly designed system, tape roughness is the limit of head-to-tape separation, usually <10 fm.

(2) Changes.—(a) Head contamination is the debris attached to the head, which causes the tape to lift away from the head, forming a tent-like deformation of the tape. This tent does not move or change shape until the contamination is removed. (b) Tape contamination includes particles attached to the tape, resulting in a tent that moves across the head with the tape. (3) Effective.—(a) The actual distance from the magnetic storage material on the tape to the top of the active magnetic core material at the read or write gape. (b) The effective AI-11 head-to-tape separation is usually somewhat larger than the mechanical head-to-tape separation.

TAPE TRANSPORT—(1) The mechanism that extracts magnetic tape from a storage device, moves it across magnetic heads at a controlled speed and then feeds it into another storage device. (2) Typical storage devices are tape loops, bins, reels, cassettes, and cartridges. (3) The tape transport is the part of a magnetic tape recorder/reproducer system that normally consists of magnetic heads, magnetic tape, transport, record electronics, and reproduce electronics. TEAR STRENGTH—The force required to initiate and/or propagate a tear in a specially shaped specimen of tape or base film.

TOTAL THICKNESS—The sum of the thicknesses of the base film and the magnetic coating, as well as back coating, when applied. The total thickness governs the length of tape that can be wound on a given reel. TRACK—An area of the tape's surface that coincides with the location of the recorded magnetization produced by one record gap. TRACK WIDTH—The width of the track corresponding to a given record gap. UBE—(See upper band edge.) UNDERCUT—(See washout.) UNIFORMITY—The extent to which the output remains free from variations in amplitude.

Uniformity is usually specified as the positive and negative deviations from the average output within a roll of tape. UPPER BAND EDGE (UBE)—The upper band edge of the recorder/reproducer response (usually at the -3dB point). VOID—An area where material is missing on the surface of a tape or on a head's track. WASHOUT—(1) A hard-coated head whose magnetic core material has a much higher wear rate than the coating. (2) The radius of curvature of the core material will be larger than the surrounding coating of the softer material, which could even be undercut, possibly causing an increase in the head-to-tape separation. (3) Also called undercut.

WAVELENGTH—The distance along the length of a sinusoidally recorded tape corresponding to one cycle. WAVINESS—(1) A non-flat head's top surface perpendicular to the tape motion due to different wear rates in top surface materials. The harder material will be up. The head core is usually the harder material; therefore, there will be increased head-to-tape contact pressure at the cost of tape life. (2) Can occur during break-in or field use. WEAR ABILITY—(See durability.) WEAR PRODUCT—Any material that is detached from the tape during use.

WEAR TEST—(See durability.) AI-12 WIND—The way in which tape is wound onto a reel. An A-wind is one in which the tape is wound so that the coated surface faces toward the hub. WINDER/CLEANER—A device that winds and cleans magnetic tape to restore it to a near-new condition, providing the tape has not been physically damaged. WOW AND FLUTTER—(1) The changes in signal-output frequency caused by tape-speed variations occurring at relatively low and relative high rates, respectively. (2) Wow is no longer used, but is incorporated into the flutter measurement.

WRITE FEEDTHROUGH—(1) The magnetic coupling from the write track to a read track in the read/write head. (2) Also called crossfeed and crosstalk. ZERO-MODULATION NOISE—(See noise.)