BUSES AND ADAPTER

ACCELERATOR BOARD:
A type of expansion board that makes a computer faster by adding a faster CPU or FPU. Accelerator boards provide a relatively inexpensive way to increase the performance of a computer.

There are many accelerator boards for Macintoshes and PCs. For example, a 486 accelerator board contains an Intel 80486 microprocessor. By adding it to an older PC with a 286 or 386 processor, you can effectively turn the computer into a 486 PC.

Note, however, that adding an accelerator board to a computer affects only the speed of the CPU (and sometimes main memory). This may not have a large effect on your applications if the limiting factors are the speed of the disk drive or the bus. If you want to increase performance of an old computer, you are probably better off buying a modern disk drive or adding extra memory.

Most modern computers are designed to accept simpler upgrades. Built into the motherboard is a socket in which the CPU sits. It is usually possible simply to remove the CPU and replace it with a faster model. This is particularly easy if the socket is a zero insertion force (ZIF) socket.


ACCESS BUS:

A serial communications protocol developed by Philips Semiconductors and Digital Equipment (DEC) in 1985 for connecting peripheral devices to a computer. Access.bus is designed for hassle-free installation and configuration of relatively low-speed devices, such as keyboards, monitors, and printers. Access.bus uses a bus topology, which enables it to support up to 125 devices.

A competing standard, Universal Serial Bus (USB), is quickly becoming the serial standard of the future.

ADAPTER:

The circuitry required to support a particular device. For example, video adapters enable the computer to support graphics monitors, and network adapters enable a computer to attach to a network. Adapters can be built into the main circuitry of a computer or they can be separate add-ons that come in the form of expansion boards.

ADB:

Abbreviation of Apple Desktop Bus, a type of communications pathway built into all versions of the Apple Macintosh computer since the SE. It is used to connect low-speed input devices such as the keyboard and mouse. ADB ports are designated with the icon. A single ADB port can support as many as 16 simultaneous input devices.

ADD-IN:

A component you can add to a computer or other device to increase its capabilities. Add-ins can increase memory or add graphics or communications capabilities to a computer. They can come in the form of expansion boards, cartridges, or chips. The term add-in is often used instead of add-on for chips you add to a board that is already installed in a computer. In contrast, add-on almost always refers to an entire circuit board.

A software program that extends the capabilities of larger programs. For example, there are many Excel add-ins designed to complement the basic functionality offered by Excel. In the Windows environment, add-ins are becoming increasingly common thanks to OLE 2.0.

ADD-ON:

Refers to a product designed to complement another product. For example, there are numerous add-on boards available that you can plug into a personal computer to give it additional capabilities. Another term for add-on board is expansion board.

Add-on products are also available for software applications. For example, there are add-on report generation programs that attach to popular database products such as dBASE, giving them additional report-generation and graphics capabilities.

The terms add-on and add-in are often, but not always, used synonymously. The term add-in can refer to individual chips you can insert into boards that are already installed in your computer. Add-on, on the other hand, almost always refers to an entire circuit board, cartridge, or program.

ADDRESS BUS:

A collection of wires connecting the CPU with main memory that is used to identify particular locations (addresses) in main memory. The width of the address bus (that is, the number of wires) determines how many unique memory locations can be addressed. Modern PCs and Macintoshes have 32 address lines, which enables them to access 4GB (gigabytes) of main memory.

AT BUS:

The expansion bus on the IBM PC/AT and compatible computers. The bus is the collection of wires and electronic components that connect all device controllers and add-in cards. The controllers are the components that attach to peripheral devices. The bus, therefore, is the main highway for all data moving in and out of the computer.

The AT bus, which runs at 8 megahertz and has a 16-bit data path, is the de facto standard for PCs. Because all IBM PCs (until the high-end PS/2 models) had an AT bus, it has been possible for manufacturers to produce expansion boards that will work with any PC.

As processors have become more powerful, and applications more demanding, the AT bus has turned out to be the chief bottleneck in PCs. In response, IBM introduced the Micro Channel Architecture (MCA) in 1987. However, MCA was not accepted by the computer industry because it was not backward compatible with the AT-bus, so IBM has been forced to drop it.
A more successful alternative to the AT bus is the Extended Industry Standard Architecture (EISA), a high-speed 32-bit bus architecture developed by a group of IBM’s competitors. Unlike MCA, EISA is backward compatible with the AT bus, so a computer equipped with an EISA bus can accept AT or EISA expansion boards.

While EISA has had limited success, its speeds are still insufficient for modern graphical applications. The most common solution to bypassing the AT-bus bottleneck is to include a local bus on the motherboard. A local bus communicates directly with the processor rather than using the standard computer bus. Currently, there are two competing standards for local buses: VESA local bus (VL-bus), promoted by the VESA standards group, and Peripheral Component Interconnect (PCI), designed and promoted by Intel.

The AT bus is sometimes referred to as the ISA bus, which stands for Industry Standard Architecture. However, ISA also includes the XT bus, which is an 8-bit version of the AT bus.

BURST MODE:

A data transmission mode in which data is sent faster than normal. There are a number of techniques for implementing burst modes. In a data bus, for example, a burst mode is usually implemented by allowing a device to seize control of the bus and not permitting other devices to interrupt. In RAM, burst modes are implemented by automatically fetching the next memory contents before they are requested. This is essentially the same technique used by disk caches.
The one characteristic that all burst modes have in common is that they are temporary and unsustainable. They allow faster data transfer rates than normal, but only for a limited period of time and only under special conditions.

BUS:

A collection of wires through which data is transmitted from one part of a computer to another. You can think of a bus as a highway on which data travels within a computer. When used in reference to personal computers, the term bus usually refers to internal bus. This is a bus that connects all the internal computer components to the CPU and main memory. There's also an expansion bus that enables expansion boards to access the CPU and memory.
All buses consist of two parts -- an address bus and a data bus. The data bus transfers actual data whereas the address bus transfers information about where the data should go.
The size of a bus, known as its width, is important because it determines how much data can be transmitted at one time. For example, a 16-bit bus can transmit 16 bits of data, whereas a 32-bit bus can transmit 32 bits of data.
Every bus has a clock speed measured in MHz. A fast bus allows data to be transferred faster, which makes applications run faster. On PCs, the old ISA bus is being replaced by faster buses such as PCI.
Many PCs made today include a local bus for data that requires especially fast transfer speeds, such as video data. The local bus is a high-speed pathway that connects directly to the processor.
Several different types of buses are used on Apple Macintosh computers. The fastest and most sophisticated is called the NuBus expansion bus.
In networking, a bus is a central cable that connects all devices on a local-area network (LAN). It is also called the backbone.

CARD BUS:

The 32-bit version of the PCMCIA PC Card standard. In addition to supporting a wider bus (32 bits instead of 16 bits), CardBus also supports bus mastering and operation speeds up to 33 MHz.

CONTROLLER:

A device that controls the transfer of data from a computer to a peripheral device and vice versa. For example, disk drives, display screens, keyboards, and printers all require controllers.
In personal computers, the controllers are often single chips. When you purchase a computer, it comes with all the necessary controllers for standard components, such as the display screen, keyboard, and disk drives. If you attach additional devices, however, you may need to insert new controllers that come on expansion boards.
Controllers must be designed to communicate with the computer's expansion bus. There are three standard bus architectures for PCs -- the AT bus, the Extended Industry Standard Architecture (EISA), and the SCSI bus. When you purchase a controller, therefore, you must ensure that it conforms to the bus architecture that your computer uses.

DIP:

Acronym for dual in-line package, a type of chip housed in a rectangular casing with two rows of connecting pins on either side.

DIP SWITCH:

A DIP (dual in-line package) switch is a series of tiny switches built into circuit boards. The housing for the switches, which has the same shape as a chip, is the DIP.DIP switches enable you to configure a circuit board for a particular type of computer or application. The installation instructions should tell you how to set the switches. DIP switches are always toggle switches, which means they have two possible positions -- on or off. (Instead of on and off, you may see the numbers 1 and 0.)
One of the historic advantages of the Macintosh over the PC was that it allowed you to configure circuit boards by entering software commands instead of setting DIP switches. However, the new Plug & Play standard developed by Microsoft makes DIP switches obsolete for PC expansion cards too.

DSP:

Short for digital signal processing, which refers to manipulating analog information, such as sound or photographs that has been converted into a digital form. DSP also implies the use of a data compression technique.
When used as a noun, DSP stands for digital signal processor, a special type of coprocessor designed for performing the mathematics involved in DSP. Most DSPs are programmable, which means that they can be used for manipulating different types of information, including sound, images, and video.

EDGE CONNECTOR:

The part of a printed circuit board that plugs into a computer or device. The edge connector generally has a row of broad metallic tracks that provide the electrical connection.

EIDE:

Short for Enhanced IDE, a new version of the IDE mass storage device interface standard developed by Western Digital Corporation. It supports data rates of between 4 and 16.6 MBps, about three to four times faster than the old IDE standard. In addition, it can support mass storage devices of up to 8.4 gigabytes, whereas the old standard was limited to 528 MB. Because of its lower cost, enhanced EIDE has replaced SCSI in many areas.
EIDE is sometimes referred to as Fast ATA or Fast IDE, which is essentially the same standard, developed and promoted by Seagate Technologies. It is also sometimes called ATA-2.There are four EIDE modes defined. The most common is Mode 3, which transfers data at a rate of 11.1 MBps. Mode 4 supports transfer rates of 16.6 MBps. Currently under development is a new mode, called ATA-3 or Ultra ATA, that supports transfer rates of 33 MBps.

EISA:

Acronym for Extended Industry Standard Architecture, a bus architecture designed for PCs using an Intel 80386, 80486, or Pentium microprocessor. EISA buses are 32 bits wide and support multiprocessing.
The EISA bus was designed by nine IBM competitors (sometimes called the Gang of Nine): AST Research, Compaq Computer, Epson, Hewlett-Packard, NEC, Olivetti, Tandy, WYSE, and Zenith Data Systems. They designed the architecture to compete with IBM's own high-speed bus architecture called the Micro Channel architecture (MCA).
The principal difference between EISA and MCA is that EISA is backward compatible with the ISA bus (also called the AT bus), while MCA is not. This means that computers with an EISA bus can use new EISA expansion cards as well as old AT expansion cards. Computers with an MCA bus can use only MCA expansion cards.
EISA and MCA are not compatible with each other. This means that the type of bus in your computer determines which expansion cards you can install.
Neither EISA nor MCA has been very successful. Instead, a new technology called local bus is being used in combination with the old ISA bus. There are two competing local bus standards -- PCI and VL-bus -- but it now seems that PCI will become the de facto standard for PCs, and possibly for Macintoshes as well.

EXPANSION BOARD:

A printed circuit board that you can insert into a computer to give it added capabilities. For example, all of the following are expansion boards:
· video adapters
· graphics accelerators
· sound cards
· accelerator boards
· internal modems
Expansion boards for PCs can be half-size (also half-length) or full-size (also full-length). Most PCs have slots for each type of board. A half-size board is sometimes called an 8-bit board because it can transmit only 8 bits at a time. A full-size board is called a 16-bit board. In addition, some expansion boards are designed to operate with a local bus, such as PCI.
Expansion boards are also called adapters, cards, add-ins, and add-ons.

EXPANSION BUS:

A collection of wires and protocols that allows the expansion of a computer by inserting printed circuit boards (expansion boards). Traditionally, PCs have utilized an expansion bus called the ISA bus. In recent years, however, the ISA bus has become a bottleneck, so nearly all new PCs have a PCI bus for performance as well as an ISA bus for backward compatibility.

EXPANSION SLOT:

An opening in a computer where a circuit board can be inserted to add new capabilities to the computer. Nearly all personal computers except portables contain expansion slots for adding more memory, graphics capabilities, and support for special devices. The boards inserted into the expansion slots are called expansion boards, expansion cards, cards, add-ins, and add-ons.
Expansion slots for PCs come in two basic sizes: half- and full-size. Half-size slots are also called 8-bit slots because they can transfer 8 bits at a time. Full-size slots are sometimes called 16-bit slots. In addition, many modern computers include local-bus slots for expansion boards that connect directly to the machine’s local bus.

EXTERNAL BUS:

A bus that connects a computer to peripheral devices. Two examples are the Universal Serial Bus (USB) and FireWire.

ISA BUS:

The bus architecture used in the IBM PC/XT and PC/AT. It's often abbreviated as ISA (pronounced eye-sa) bus. The AT version of the bus is called the AT bus and has become a de facto industry standard. Since the late 80s, the industry has been searching for a successor to the ISA bus, which is not sufficient for modern devices and applications. It now appears that the successor will be the PCI local bus architecture. Most computers made today include both an AT bus for slower devices and a local bus for devices that need better bus performance.
In 1993, Intel and Microsoft introduced a new version of the ISA specification called Plug and Play ISA. Plug and Play ISA enables the operating system to configure expansion boards automatically so that users do not need to fiddle with DIP switches and jumpers.

IRQ:

Abbreviation of interrupt request line, and pronounced I-R-Q. IRQs are hardware lines over which devices can send interrupt signals to the microprocessor. When you add a new device to a PC, you often need to set its IRQ number by setting a DIP switch. This specifies which interrupt line the device may use. IRQ conflicts are a common problem when adding expansion boards, but the new Plug and Play ISA specification may remove this headache.

JUMPER:

A metal bridge that closes an electrical circuit. Typically, a jumper consists of a plastic plug that fits over a pair of protruding pins. Jumpers are sometimes used to configure expansion boards. By placing a jumper plug over a different set of pins, you can change a board's parameters.

LOCAL BUS:

A data bus that connects directly, or almost directly, to the microprocessor. Although local buses can support only a few devices, they provide very fast throughput. Most modern PCs include both a local bus, for video data, as well as a more general expansion bus for other devices that do not require such fast data throughput.

MCA:

A bus architecture for older PCs. It is called a bus architecture because it defines how peripheral devices and internal components communicate across the computer's expansion bus. Introduced by IBM in 1987, MCA was designed to take the place of the older AT bus, the architecture used on IBM PC-ATs and compatibles. For a variety of reasons, however, the industry never accepted the new architecture.

NUBUS:

The expansion bus for all versions of the Macintosh computers starting with the Macintosh II. Apple has indicated that sometime in the future it may replace NuBus with PCI.

PC CARD:

A computer device packaged in a small card about the size of a credit card and conforming to the PCMCIA standard.

PCI:

Acronym for Peripheral Component Interconnect, a local bus standard developed by Intel Corporation. Most modern PCs include a PCI bus in addition to a more general ISA expansion bus. Many analysts, however, believe that PCI will eventually supplant ISA entirely. In addition, Apple Computer has indicated that future versions of the PowerMac will use PCI. PCI is a 32-bit bus, but supports a 64-bit extension for new processors, such as the Pentium. It can run at clock speeds of 33 or 66 MHz. At 32 bits and 33 MHz, it yields a throughput rate of 132 MBps. 64-bit implementations running at 66 MHz provide 524 MBps.
Although it was developed by Intel, PCI is not tied to any particular family of microprocessors.

PCMCIA:

Short for Personal Computer Memory Card International Association, and pronounced as separate letters, PCMCIA is an organization consisting of some 500 companies that has developed a standard for small, credit card-sized devices, called PC Cards. Originally designed for adding memory to portable computers, the PCMCIA standard has been expanded several times and is now suitable for many types of devices. There are in fact three types of PCMCIA cards. All three have the same rectangular size (85.6 by 54 millimeters), but different widths
· Type I cards can be up to 3.3 mm thick, and are used primarily for adding additional ROM or RAM to a computer.
· Type II cards can be up to 5.5 mm thick. These cards are often used for modem and fax modem cards.
· Type III cards can be up to 10.5 mm thick, which is sufficiently large for portable disk drives.
As with the cards, PCMCIA slots also come in three sizes:
· A Type I slot can hold one Type I card
· A Type II slot can hold one Type II card or two Type I cards
· A Type III slot can hold one Type III card or a Type I and Type II card.
Ideally, you should be able to exchange PC Cards on the fly, without rebooting your computer. For example, you should be able to slip in a fax modem card when you want to send a fax and then, when you’re done, replace the fax modem card with a memory card. Unfortunately, because of deficiencies in the initial standard and poor implementations by card manufacturers, this has sometimes not worked as planned. However, the standard appears to be reaching a level of maturity where such hot plugging installation is becoming a reality.
Some analysts believe that the PC card has the potential to become the dominant expansion technology for desktop model computers as well as portable computers.

PLUG AND PLAY:

Refers to the ability of a computer system to automatically configure expansion boards and other devices. You should be able to plug in a device and play with it, without worrying about setting DIP switches, jumpers, and other configuration elements. Since the introduction of the NuBus, the Apple Macintosh has been a plug-and-play computer, while the PC has not. This may change, however, as manufacturers adopt the new Plug and Play (PnP) specification created by Microsoft and Intel in 1993.

PnP:

Short for Plug and Play, a technology developed by Microsoft and Intel that supports plug-and-play installation. PnP is built into the Windows 95 operating system, but to use it, the computer’s BIOS and expansion boards must also support PnP.

PRINTED CIRCUT BOARD:

Sometimes abbreviated PCB, a thin, rectangular plate on which chips and other electronic components are placed. Computers consist of one or more boards, often called cards or adapters. Circuit boards fall into the following categories:
motherboard: The principal board that has connectors for attaching devices to the bus. Typically, the mother board contains the CPU, memory, and basic controllers for the system. On PCs, the motherboard is often called the system board. expansion board: Any board that plugs into one of the computer's expansion slots. Expansion boards include controller boards, LAN cards, and video adapters.
daughterboard: Any board that attaches directly to an expansion board.controller board: A special type of expansion board that contains a controller for a peripheral device. When you attach new devices, such as a disk drive or graphics monitor, to a computer, you often need to add a controller board.Network Interface Card (NIC): An expansion board that enables a PC to be connected to a local-area network (LAN).
video adapter: An expansion board that contains a controller for a graphics monitor.

SCAM:

Short for SCSI Configuration Automatically, a subset of the PnP specification that provides plug-and-play support for SCSI devices.

SLOT:

An opening in a computer where you can insert a printed circuit board. Slots are often called expansion slots because they allow you to expand the capabilities of a computer. The boards you insert in expansion slots are called expansion boards or add-on boards.Do not confuse slots with bays. Bays are sites within the computer where you can install disk drives.

VL-BUS:

Short for VESA Local-Bus, a local bus architecture created by the Video Electronics Standards Association (VESA). Although it was quite popular in PCs made in 1993 and 1994, it has been overshadowed by a competing local bus architecture called PCI.

VME BUS:

(VersaModule Eurocard bus) A 32-bit bus developed by Motorola, Signetics, Mostek and Thompson CSF. It is widely used in industrial, commercial and military applications with over 300 manufacturers of VMEbus products worldwide. VME64 is an expanded version that provides 64-bit data transfer and addressing.