T-1
The telephone company lease of DS1 high-speed digital data
lines for use by Wide Area Networks (WANs) "backbone"
communications between world-wide locations. T-1 lines are
expensive, yet usually cost-effective for such large
networks. Local Area Networks (LANs) require gateways for
accessing T-1 circuits, because data probably will be
converted to a PCM (pulse code modulation) format that
conforms to Bell System standards. T-1 circuits have
sufficient bandwidth for handling 24 simultaneous 56- to 64-
Kbps channels, (a DS0 rate) on a line with a total capacity
of 1.544-mbps (megabytes-per-second) (a DS1 rate).
Multiplexers may use software to control availability and to automate T-1 operational functions such as circuit path selection, traffic rerouting (e.g., after T-1 line failure to switch to a non-lease line) and bandwidth contention. The multiplexer-T-1 lease line combination lets PBX and networks extend their services over the T-1 line.
Alternatives to high-speed T-1 lines, are provided by Sprint™, MCI™. They offer "fractional T-1" service which provide single-channel data rates up to the full 1.544-bps T-1 capacity. (Rather than dividing bandwidth between multiple channels.)
Local phone companies may also offer T-2 (DS2) with 96 voice channels, T-3 (DS3) with 672 channels, and T-4 (DS4) with 4,032 channels. Analog-voice lines and Analog-data lines offer speeds up to 9.6-Kbps on lines with a capacity of 56- to 64- Kbps. (Contrast this with standard phone lines which can handle a maximum of 24-Kbps.
The local phone companies provide a variety of other, less costly lease lines. Among them are: Telemetry "sub-voice" lines (used for low-speed teleprinters and alarms) that carry data at about 100-bps (bits-per-second). These lines are considered "dirty" with noise; errors occur.
Tablets
These data-entry devices are also known as Graphics Tablets. A pressre-sensitive tablet with pen (or handheld "cursor" with programable buttons and crosshairs) may be implemented with one as a transmitter and the other as a receiver.
For most devices, the pen is the transmitter and the tablet is the receiver. A coil in the pen generates a magnetic field which, by its proximity, effects a wire grid inside the tablet's "active area." A received signal representing the grid coordinates of the field is intrepreted by the tablet's microprocessor which then sends them to a computer for onscreen interaction with a compatible software application that can interpret the pressure data.
Each point on the grid corresponds to a pixel location onscreen. This is "absolute positioning." Touching any point on the tablet immediately moves the onscreen cursor to that location. This is a faster, more accurate and natural way of cursor movement than occurs with a mouse or trackball which must be dragged or rolled to move the cursor in a path across the screen to a another location.
Many pens have one or two side buttons which may be programed to perform such functions as an "undo" command. A button is often used to activate an erraser located on the end of the pen opposite its "point." And some errasers may be programed for other functions; such as, an airbrush for highlighting and texturing a 3-dimention image. A pen's point may also be tipped with pencil lead or ball-point ink so that a "hard copy" of an image can be drawn on a sheet of paper laying on top of the tablet, as the onscreen image is drawn.
Tablets may also have plastic covers to hold drawings in place, over the active area which corresponds to the monitor's screen, so that the image can be traced.
The active area may also have menu strips for many organizational purposes; for example, selecting predefined art elements such as a door, chair or window as may be used in a architectural drawing. Larger tablets may include strips of programable buttons in the frame around the active area; along its top or sides. Buttons can control both operating system functions like opening, saving, and printing the file; as well as, application-specific functions, such as a "plugin" utility that alters in some way the onscreen image, or the "feel" and sensitivity of the pen.
Tape
A casette which holds a thin plastic ribbon coated with an iron oxde compound. When data is recorded, electrical pulses magnetically change the positive and negative orientations of portions of the compound; when read, the movement of the tape's compound beneith the read/write head generates electrical pulses to recreate the data. This process is similar to the one used by disk-based magnetic media; however, data is stored sequential on the tape, the next block of data is recorded after the last block. The whole tape may have to be read to locate a specific block of data.
Tape drives
Alternatives include several cassette options. The most common are the quarter-inch tape cartridges (QIC) which are available in two standard sizes, the DC600 cartridge (the DC9135 has the same size) and DC2000 minicartridge. There are thirty six QIC standards which cover interfaces, tape format classes and data compression. (Drives supporting the QIC-40 and QIC-80 standards can use the computer's floppy drive controller.) Other references: QIC.
Also reference DDS (Digital Data Storage) 4mm format magnetic tape standards and drives.
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Tape and Reel
The chip packaging for automated pick & placement equipment. Simply stated, the reel stores dozens, even hundreds of chips stuck to a tape and feeds them into a device that places them accurately onto circuitboards.
TCU
Transfer control unit. Its functions are similar to the Data Transfer Unit which transfers data between WM and Cache Memory.
TDR or Time-domain reflectometer
It is a sonar-or radar-like diagnostic device that analyzes reflected electrical pulses to detect cable defects (faults). A TDR measures the length of a cable by the time it takes for the reflected pulse to return to the TDR, multiplied by the NVP speed.
Telex
A teleprinter dial network sponsored by Western Union. It uses baudot code.
Terabyte (TB)
A terabyte is a unit of measure equal to 1,024 GigaBytes, or 1,048,576 MB, or 1,073,741,824 KB.
3D-RAM
Three-dimential high-end graphics RAM chips.
3H (or "third" )
Label is used to indicate a Third-height drive.
TM Translate Mode (or just Translate)
It is the translation of the drive's physical specifications into logical specifications that are within the computer's BIOS and DOS limitations of having no more than 16 heads, 1,024 cylinders and 63 sectors per track and the resulting maximum data storage capacity of 528MB. Many BIOSes created between 1992 and 1996 only recognize a maximum of 2.113 GB, excess capacity is inaccessible unless logically allocated by partition as a different drive.
TP
Transfer Processor inside a (RISC) processor chip. Its functions are similar to the Control Processor which controls the overall operation of the chip's arithmetic or IO cluster.
Transfer Rate ( TR )
This number indicates the theoretical time it takes data to move between the drive and the controller&emdash;in bits per second (bps) or bytes per second (Bps). A drive's actual sustained data transfer rate is determined by the data pathway and therefore it is usually less than the functional limits of the interface. For a hard drive the pathway can be: disk acces to drive's controller to buffer cache memory (if any) to host/bus adapter to system's internal bus to system DMA to RAM to CPU or video RAM to DSP (if any) to monitor.
Typical internal system bus rates: ISA bus is 1.5 MBps, EISA 12 MBps, NuBus 17 MBps, PCI 65MBps.
Typical external system bus rates: IDE is 2 to 3 MBps, ATAPI provides a high-speed option for IDE devices of from 11 to 13 MBps. SCSI-1 has rates from 1.4 to 5MBps transfers. SCSI-2 impelmentations range from 10 to 20MBps.
For multimedia applications, the CPU/bus and software overhead typically cut the effective data rate in half, getting the video data into the computer through the host/bus adapter and through the video digitizing/compression board. If the system's CPU includes an MMX (multimedia extension) or multi&endash;media coprocessor, software must be at least 32-bit and code-enabled to take full advantage of the faster processing capabilities.
For optimum multimedia performance, a hard drive's advertised data transfer rate should equal twice the desired video rate (e.g., 3 MBps for 1.5 MBps).
The transfer rate of compressed stored data (labeled as: cp=) , will be slightly less than than a simple multiple of the compression ratio because compression algorithms are optomized for storage rather than transmission. A manufacturer's specification for transmitting uncompressed data in a compressed format may not include the time to compress the data.
Other reference: Average Access Time.
Transformer
A power transformer is An electrical component. It is used to alter input AC voltage and current levels and some of them also isolate one circuit from another. Transformers are a combination of two or more inductors working together: one primary input coil, one or more output coils and a core structure, usually iron, between them. Typically, the primary and secondary coils are wound around the core. The windings (enamel-covered magnetic wire) are often copper; the more copper and iron, the greater the output.
An AC signal is constantly changing in strength. When applied to the primary coil's windings, the magnetic field it creates is subject to the same fluctuations. A "magnetic coupling" occurs between primary and secondary windings. When the primary's field intersects the secondary's windings&emdash;it induces (creates) a duplicate AC signal. Voltage and current are in balance because the power going into a transformer equals the power out of it (minus heat generated by resistance in the wires, and minus some magnetic field loss).
Increasing the total number of parallel windings, increases the current; increasing the number of secondary windings over the number of primary windings increases voltage. This relationship between the number of primary windings to secondary windings is the "turns ratio." For example, if the input is 10 volts of alternating current (10 Vac), and there are 500 primary windings and 1000 secondary windings, multiplying the 10 Vac by the 1-to-2 ratio creates a 20 Vac output. (Output current would be decreased to maintain balance.)
Stepdown transformers have more primary windings than secondary windings; the ratio is reversed&emdash;less voltage and more current.
Transformer circuits: Vin is the source of the signal, its impedance is set by the R's (resister). The Vin pulses are sent to the transformer's primary inductance (L) winding L'p. The magnetic field of L'p induces a duplicate field in the secondary L's1 and L's2 windings. That field is represented by the turns ratio Pn:Sn, primary to secondary.
The two secondary windings L's1 and L's2, may be connected. If so, the link will be either a parallel 1 connection (with a 24 volts at 1 amp output), or a serial 2 connection (with two 12v at 1a outputs). A secondary winding may also have a center tap 3 added to reduce output. L's2 is divided into L's2a and L's2b. The second half, L's2b (with its 6v at 1a output), is not used. A secondary may be terminated by any or all of these components: R'st (a resistor terminating two or more secondary windings connected in a series), R'pt (a resistor terminating two or more secondary windings connected in parallel), and C'pt (a capacitor terminating two or more secondary windings connected in parallel). The dot (near the windings) is a phasing mark. The transformer's core: D.
The primary side is usually the hot side; look for the hot ground. The secondary side may be cold; look for the ground. For each transformer, a VA (volt-ampere) rating is used to reflect the total current and voltage output of its secondary load. For example, a 6VA transformer could have one secondary winding with a 6 volt at 1 amp output, or two secondary windings, each with a 6 volt at 0.5 amp output, or a series of two secondary windings, each with a 12 volt at 0.25 amp pÚput, etc. (Multiplying 12 by 0.25, then by 2 equals 6 volts.)
Inside a transformer, each inductor coil is covered by insulation. Heat, in time, will breakdown the insulation and thereby lower the coil's resistance. The coil responds to the loss by drawing ever more current until onfõkf its winding is shorted (broken). (If there are multiple transformers and a secondary transformer fails, there may be no discernable overheating.)
Note: PC What's The Problem? includes identification, test, repair and replacement suggestions.
Transistor
A semiconductor devices that control electrical output based on an input electrical signal. They may also provide power amplification. Transistors have three or more terminal-leads which may have different functions within the two general families, Bipolars and FETs. And the terminal-leads may have different sequence and arangements.
Bipolar transistors are characterized by the function of their base (B), emitter (E) and collector (C) terminal-leads. Typically, the base receives is the input signal. The emitter is tied to ground (usually through a path that includes one or more resistors). The collector provides the output signal. One alternative receives the input signal through the collector, the base is grounded and the signal is output through the emitter.
There are three types of Bipolar transistors: NPN, PNP and Phototransistor:
NPN transistors require positive base and collector voltages&emdash;with respect to the emitter&emdash;before they can conduct current. As the positive voltage through the base increases, more current is passed through the collector until the transistor reaches saturation. NPNs are also known as N-channel devices.
PNP transistors require negative base and collector voltages&emdash;with respect to the emitter&emdash;before they can conduct current. As the negative voltage through the base increases, more current is passed through the collector until the transistor reaches saturation. PNPs are also known as P-channel devices.
Phototransistors use photons of light as a signal source. The light enters the transistor through a clear quartz or plastic window and it liberates its electrons when it strikes the transistor's base conductor, thereby producing current.
Optocoupler (or optisolator) sensors can be made by placing a phototransistor opposit an LED (light-emitting diode). When something prevents the LED's light from striking the optocoupler, no signal is generated. A printer, for example, uses a optocoupler to detect an empty paper-feed path. If there is no paper between the LED and optocoupler, printing is prevented. A paper-out signal may also be sent to a computer to stop it from sending data until paper is in the paper feed-path. FETs (field-effect transistors) and can operate as either switches or amplifiers.
There are two types of FET transistors, Junction FETs (JFETs) and MOSFETs. Both types are sensitive to ESDs (electrostatic discharges) and can be easily damaged by improper handling.
JFETs are characterized by the function of their gate (G), source (S), and drain (D) terminal-leads. Typically, the gate receives is the input or control signal. The source is tied to ground (usually through a path that includes one or more resistors). The drain provides the output signal.
Current flows from the drain to source when no voltage is applied to the gate terminal. That current flow can be controled by adjusting the gate's input voltage. The control signal in an N-channel FET is negative at the gate; in a P-chanel FET it is positive at the gate. The greater the control signal's voltage, the lesser the flow of current through the transistor.
MOSFETs (metal-oxide semiconductor FETs), are more often used in digital integrated circuits (ICs) than as a single device.
Note: PC What's The Problem? includes identification, test and replacement suggestions.
Triacs
They are referenced with other Diodes.
TSOP (Thin, Small-Outline Package)
These RAM chips are thinner and have shorter legs than standard SIMM chips. A TSOP chip is thinner than the memory module board it is mounted on! Contrast with reference: VTSOP.
Type-1 Cable.
Four versions of this data communications cable are available: Indoor Non-plenum (IBM F. Eq. Ref. #4716748), Outdoor (IBM F. Eq. Ref. #4716734), and Indoor Plenum (IBM F. Eq. Ref. #4716749). They are long-distance cables used for Token Ring LAN's Backbone, between MAUs, between floors, and buildings. (Review the Type-6 cable reference.)
Outdoor Type-1 IBM-standard cable has a corrugated metalic shield that makes it suitable for underground conduit and aerial installations. Type-9 cables may be substituted to reduce cost when performance and distance limitations are not restrictive.
Plenium Type-1 is insulated with a teflon jacket (not PVC). Type-1 cable is thicker than Type-9 cable and therefore has lower attenuation, loss of electrical energy as it travels along a cable.
Specifications: For Type-1, the maximum attenuation is 22.00-dB/km at 4MHz, 45.00-dB/km at 16MHz; DC resistance (maximum ohms/1000ft) is 57.1; and an impedance of shielded cables 150 ohms nominal at 4 or 16MHz frequency. Capacitance (unbalance, max pF/km): 1500 pF pair to ground.
Also reference: Cables and Connectors.
Note: PC What's The Problem? includes identification, installation, test and replacement suggestions.
Type-1A Cable
This IBM-standard shielded twisted-pair (STP) cable is an enhanced-performance version of Type-1 cables, with the additional capability of carrying video signals. It was designed for FDDI network installation supporting cables longer than 60 meters (198 feet): Capacitive Unbalance (at 25°C) is 100 pf/km at 1 KHz, DC Resistance (at 25°C) is 57.1 ohms /km.
Construction: Made from two twisted pairs of 22-AWG (American Wire Gauge) solid-copper-wire conductors, each pair is enclosed in a foil shield of metal-backed mylar. A second foil shield and a braided shield enclose the two twisted pairs beneath the cable's outer PVC jacket. (The shields have two functions, protection from electrical "noise," and electrical grounding.)
Note: PC What's The Problem? includes identification, installation, test and replacement suggestions.
Type-2 Cable
These IBM-standard voice/data communications cables are available in either plenum or non-plenum versions. Made from two twisted pairs of 22-AWG solid-copper-wire conductors enclosed in braided-shielding under a cable jacket of PVC or for plenium installation&emdash;teflon. (The same as in a Type-1 cable.) Four additional unshielded twisted pairs of 22-AWG solid-copper-wire conductors are used for voice communications (often terminated with a RJ11 telephone plug). (IBM F. Eq. Ref. #4716738.)
Specifications: For Type-2, maximum attenuation is 22.00-dB/km at 4MHz, 45.00-dB/km at 16MHz; DC resistance (maximum ohms/ /1000ft) is 57.1; and an impedance of shielded cables 150-ohms nominal at 4 or 16MHz frequency, unshielded cables 100-ohms nominal at 4MHz frequency. Capacitance (unbalance, max pF/km): 1500 pF pair to ground. (IBM F. Eq. Ref. #4716748.)
For FDDI networks using cables longer than 60 meters (198 feet) IBM specifies Type 2A 150-ohm shielded twisted pair (STP) cable with UL/ETL performance at frequences of 100 MHz and beyond.
Note: PC What's The Problem? includes identification, installation, test and replacement suggestions.
Type-3 Cables
These IBM-standard voice/data communications cables are more widely classed as "Telephone cables." Available in both shielded and unshielded construction, with between 3 and 600 twisted-pairs of 22- or 24-AWG solid or stranded copper with a minimum of two twists per foot. With Type-1 cable used for a Token Ring LAN backbone, Type-3 can be used for all lobe cabling with a maximum distance of 150 feet. (IBM F. Eq. Ref. #4716748.)
Specifications: The maximum attenuation is 8.00-dB/1000ft; DC resistance (maximum ohms/1000ft) is 28.4; and an impedance range of 85 to 113 ohms nominal at 1MHz frequency. Cables meet the Underwriters Laboratories, Inc. (UL) Level II performance for 100 ohm twisted-pair cable with a frequency range of 256 KHz to 16 MHz, minimum near end crosstalk (NEXT) of 54 to 23 dB, and maximum attenuation per 1000 feet of 4 to 8 dBm.
Note: PC What's The Problem? includes identification, installation, test and replacement suggestions.
Type-5 Cables
These IBM-standard Fiber Optic cables with 100/140-micron core/cladding diameter multimode optical fibers.
Specifications: The maximum attenuation is 6.00-dB/km at 850 nm, 4.0 dB/km at 1300 nm.; and an impedance range of 85 to 113 ohms nominal at 1MHz frequency. For an acceptable substitute use a 62.5/125-micron cable. (IBM F. Eq. Ref. #4716744.)
Note: PC What's The Problem? includes identification, installation, test and replacement suggestions.
Type-6 and Type-7 Cables
These are IBM-standard, short-distance cables. For Token Ring LANs, they are used as "patch cables" within a wiring closet between MAUs, and placed between a wall plate and the cable-interface of computer's LAN adapter.
Note: PC What's The Problem? includes identification, installation, test and replacement suggestions.
Type-6 cable
It has two twisted pairs of 26-AWG stranded tinned copper wire conductors enclosed in first an aluminum foil shield, then an overall braided shield, under a PVC cable jacket. (IBM F. Eq. Ref. #4716743.)
Note: PC What's The Problem? includes identification, installation, test and replacement suggestions.
Type-7 IBM-standard cable
It has only one pair of wire conductors. (IBM F. Eq. Ref. #4716746.)
Note: PC What's The Problem? includes identification, installation, test and replacement suggestions.
Type 6A shielded twisted-pair (STP) cable
It is used for FDDI network cables longer than 60 meters (198 feet).
Specifications: Capacitive unbalance (at 25°C) is 100 pf/km at 1 KHz, DC Resistance (at 25°C) is 151 ohms /km.
Note: PC What's The Problem? includes identification, installation, test and replacement suggestions.
Type-8 Cable
This cable with its flat tapered jacket is designed for placement under a carpet in a medium-traffic area. It has two shielded pairs of 26-AWG solid-copper-wire conductors enclosed in braided-shielding under a PVC cable jacket. (IBM F. Eq. Ref. #4716750.)
Note: PC What's The Problem? includes identification, installation, test and replacement suggestions.
Type-9 Cable
IBM-standard cable designed for permanent installation. This is the plenum-version of the type-6 cable. This data cable has two twisted pairs of 26-AWG stranded tinned copper wire conductors enclosed in first a foil-shield, then a braided-shield, under a non-PVC cable jacket. (IBM F. Eq. Ref. #6339583.)
Note: PC What's The Problem? includes identification, installation, test and replacement suggestions.
Type-9A shielded twisted-pair (STP) cable
It is for FDDI network cables longer than 60 meters (198 feet). Specifications: Capacitive unbalance (at 25°C) is 100 pf/km at 1 KHz, DC Resistance (at 25°C) is 151 ohms /km.
Note: PC What's The Problem? includes identification, installation, test and replacement suggestions.
References are samples only. Each one is presented in greater detail in the
Technical Research Assistant for 2001
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