Hardware Glossary

A

ACPI Advanced Configuration and Power Interface. A specification that defines a new interface to the system board that enables the operating system to implement operating system–directed power management and system configuration. Following the ACPI allows system manufacturers to build systems consistent with the OnNow design initiative for instantly available PCs.

ACPI hardware Computer hardware with the features necessary to support operating system power management and with the interfaces to those features described using the Description Tables as specified in Advanced Configuration and Power Interface Specification.

add-on devices Devices that are traditionally added to the base system to increase functionality, such as audio, networking, graphics, SCSI controller, and so on. Add-on devices fall into two categories: devices built onto the system board and devices on expansion cards added to the system through a system board connector such as PCI.

ADSL Asymmetric Digital Subscriber Line. A method for moving data over regular phone lines. An ADSL circuit is much faster than a regular phone connection, and the wires coming into the subscriber’s premises are the same (copper) wires used for regular phone service.

API Application programming interface. A set of routines that an applications program uses to request and carry out lower-level services performed by a computer operating system.

architecture A general term referring to the structure of all or part of a computer system. Also covers the design of system software, such as the operating system, as well as referring to the combination of hardware and basic software that links machines on a computer network.

ATA AT Attachment. An integrated bus usually used between host processors and disk drives. Used interchangeably with IDE.

ATAPI ATA Packet Interface. A hardware and software specification that documents the interface between a host computer and CD-ROM drives using the ATA bus.

ATM Asynchronous transfer mode. A transmission protocol that segments user traffic into small, fixed-size units called cells, which are transmitted to their destination, where they are reassembled into the original traffic. During transmission, cells from different users may be intermixed asynchronously to maximize utilization of network resources.

B

bandwidth Usually used in reference to the amount of data per unit of time that must move from one point to another, such as from CD-ROM to processor.

BIOS Basic I/O system. A set of routines that works closely with the hardware to support the transfer of information between elements of the system, such as memory, disks, and the monitor. Although critical to performance, the BIOS is usually invisible to the end user; however, programmers can access it.

bps Bits per second. The number of bits transferred per second in a data communications system. A measure of speed.

bus enumerator In a Plug and Play system, a bus device driver that detects devices located on a specific bus and loads information about devices into the hardware tree.

C

cache A special memory subsystem in which frequently used data values are duplicated for quick access.

CD-ROM Compact disc read-only memory. A 4.75-inch laser-encoded optical memory storage medium (developed by NV Philips and Sony Corporation) with the same constant linear velocity (CLV) spiral format as compact audio discs and some video discs. CD-ROM discs can hold about 550 MB of data.

CI Component Instrumentation. A specification for DMI related to the service layer.

class For hardware, the manner in which devices and buses are grouped for purposes of installing and managing device drivers and allocating resources.

class driver A driver that provides system-required, hardware-independent support for a given class of physical devices. Such a driver communicates with a corresponding hardware-dependent port driver, using a set of system-defined device control requests, possibly with additional driver-defined device control requests. Under WDM, the class driver is responsible for multiprocessor and interrupt synchronization.

COM 1. Component Object Model; the core of OLE. Defines how OLE objects and their clients interact within processes or across process boundaries. 2. Legacy serial port.

CPU Central processing unit. A computational and control unit of a computer; the device that interprets and executes instructions. By definition, the CPU is the chip that functions as the “brain” of the computer.

D

data rate The speed of a data transfer process, normally expressed in bits per second or bytes per second.

DDC Display data channel. The Plug and Play baseline for monitors. The communications channel between a monitor and the display adapter to which it is connected. This channel provides a method for the monitor to convey its identity to the display adapter.

device Any circuit that performs a specific function, such as a parallel port.

device ID A unique ASCII string for a device created by enumerators to identify a hardware device and used to cross-reference data about the device stored in the registry. Distinguishes each logical device and bus from all others on the system.

disk I/O controller Also HDC. A special-purpose chip and circuitry that directs and controls reading from and writing to a computer’s disk drive.

DLL Dynamic link library. API routines that User-mode applications access through ordinary procedure calls. The code for the API routine is not included in the user’s executable image. Instead, the operating system automatically points the executable image to the DLL procedures at run time.

DMA Direct memory access. A method of moving data from a device to memory (or vice versa) without the help of the microprocessor. The system board uses a DMA controller to handle a fixed number of channels, each of which can be used by only one device at a time.

DMI Desktop Management Interface. A framework created by the DMTF. DMTF specifications define industry-standard interfaces for instrumentation providers and management applications.

driver Kernel-mode code used either to control or emulate a hardware device.

driver stack  Device objects that forward IRPs to other device objects. Stacking always occurs from the bottom up and is torn down from the top.

DVD Optical disk storage that encompasses audio, video, and computer data.

E

ECP  Extended capabilities port. An asynchronous, 8-bit–wide parallel channel defined by IEEE 1284–1944 that provides PC-to-peripheral and peripheral-to-PC data transfers.

EISA Extended Industry Standard Architecture. A 32-bit expansion bus designed as a superset of the ISA bus. Designed to expand the speed and data width of the legacy expansion bus while still supporting older ISA cards.

enumerator  A Plug and Play device driver that detects devices below its own device node, creates unique device IDs, and reports to Configuration Manager during startup. For example, a SCSI adapter provides a SCSI enumerator that detects devices on the SCSI bus.

expansion bus  A group of control lines that provide a buffered interface to devices located either on the system board or on cards that are plugged into expansion connectors. Common expansion buses included on the system board are USB, PC Card, and PCI.

expansion card  A card that connects to an expansion bus and contains one or more devices.

expansion ROM See option ROM.

F

FDC  Floppy disk controller. A chip and associated circuitry that directs and controls reading from and writing to a computer’s disk drive.

FIFO  First in/first out. A method for processing a queue in which items are removed in the same order they were added.

filters  1. Components that provide the basic building blocks for processing data. 2. Under the WDM Stream architecture filters are also known as a functional device or multimedia processing driver. Each filter’s capability is described in part by connection points called pins. Each pin can consume and produce a data stream, such as digital audio. Specialized tasks can be solved by connecting filters through their pins into a topology, for example, to play filtered and mixed audio. 3. Under WDM, a filter is implemented as a kernel-mode entity—a device object usually implemented by a kernel driver. 4. Under ActiveMovie, a filter is a User-mode entity that is an instance of a COM object, usually implemented by a DLL.

full duplex  In terms of data flow, indicates

bi-directional data flow.

H

HCI  Host controller interface, such as the system-level interface supporting USB.

HCL  Hardware Compatibility List. See WHQL.

HCT  Hardware Compatibility Tests. A suite of tests from WHQL to verify hardware and device driver operations under a specific operating environment. These tests exercise the combination of a device, a software driver, and an operating system under controlled conditions to verify that all components operate properly.

I

IDE  Integrated Device Electronics. A type of disk-drive interface where the controller electronics reside on the drive itself, eliminating the need for a separate adapter card.

IEEE  Institute of Electrical and Electronics Engineers. Organization that develops standards.

INF file  Information file. A file created for a particular adapter that provides the operating system with information required to set up a device, such as a list of valid logical configurations for the device, the names of driver files associated with the device, and so on. An INF file is typically provided by the device manufacturer on a disk with an adapter.

INI file  Initialization file. Commonly used under Windows 3.x and earlier, INI files have been used by both the operating system and individual applications to store persistent settings related to an application, driver, or piece of hardware. In Windows NT and Windows 95, INI files are supported for backward compatibility, but the registry is the preferred location for storing such settings.

input class  The class of filters that provides an interface for HID hardware, including USB and legacy devices, plus proprietary and other HID hardware, under the WDM HID architecture.

instrumentation  A mechanism for reporting information about the state of hardware and software to enable management applications to ascertain and change the state of a system and to be notified of state changes.

integrated device  Any device—such as a parallel port or graphics adapter—that is designed on the system board rather than on an expansion card.

interface  For parameters on a connection request, a specific set of methods and properties implemented on a medium that a filter connection uses to communicate, such as a specific set of IOCTLs.

I/O  Input/output. Two of the three activities that characterize a computer (input, processing, and output). Refers to the complementary tasks of gathering data for the microprocessor to work with and make the results available to the user through a device such as the display, disk drive, or printer.

IOCTL  Input/output control. A custom class of IRPs available to User mode. Each WDM class driver has a set of IOCTLs that it uses to communicate with applications. The IOCTLs give the class driver information about intended usage by applications. The class driver performs all IOCTL parameter validation.

IPL  Initial program load. A device used by the system during the boot process to load an operating system into memory.

IRP  I/O request packet. Data structures that drivers use to communicate with each other. The basic method of communication between kernel-mode devices. An IRP is a key data structure for WDM, which features multiple layered drivers. In WDM, every I/O request is represented by an IRP that is passed from one driver layer to another until the request is complete. When a driver receives an IRP, it performs the operation the IRP specifies, and then either passes the IRP back to the I/O Manager for disposal or onto an adjacent driver layer. An IRP packet consists of two parts: a header and the I/O stack locations.

IRQ  Interrupt request. A method by which a device can request to be serviced by the device’s software driver. The system board uses a PIC to monitor the priority of the requests from all devices. When a request occurs, a microprocessor suspends the current operation and gives control to the device driver associated with the interrupt number issued. The lower the number—for example, IRQ3—the higher the priority of the interrupt. Many devices only support raising requests of specific numbers.

ISA  Industry Standard Architecture. An 8-bit (and later, a 16-bit) expansion bus that provides a buffered interface from devices on expansion cards to the internal bus.

ISDN  Integrated Service Digital Network. A set of communications standards that enable a single phone line or optical cable to carry voice, digital network services, and video.

isochronous  Refers to a communication protocol based on time slices rather than handshaking. For example, a process might have 20 percent of total bus bandwidth. During its time slice, the process can stream data.

K

kernel The core of the layered architecture that manages the most basic operations of the operating system, such as sharing the processor between different blocks of executing code, handling hardware exceptions, and other hardware-dependent functions.

kernel mode  The processor mode that allows full, unprotected access to the system. A driver or thread running in kernel mode has access to system memory and hardware.

kernel-mode driver  Driver for a logical, virtual, or physical devices.

L

LAN  Local area network. A group of computers and other devices dispersed over a relatively limited area and connected by a communications link that enables any device to interact with any other device on the network. Compare with WAN.

layered driver  One of a collection of drivers that responds to the same IRPs. Layered driver describes the highest- and lowest-level drivers in a chain of layered drivers that process the same IRPs, along with all intermediate drivers in the chain.

legacy  Any feature in the system based on older technology for which compatibility continues to be maintained in other system components.

local bus  Usually refers to a system bus directly connected to the microprocessors on a system board. Used colloquially to refer to system board buses that are located closer to the microprocessor than expansion buses (that is, with less buffering), which are therefore capable of greater throughput.

M

MDL  Memory descriptor list. In Windows NT, an opaque structure, defined by Memory Manager, that uses an array of physical page frame numbers to describe the pages that back a virtual memory range.

minidriver  A hardware-specific DLL that uses a Microsoft-provided class driver to accomplish most actions through functions call and provides only device-specific controls. Under WDM, the minidriver uses the class driver’s device object to make system calls.

miniport driver  A device-specific kernel-mode driver linked to a Windows NT or WDM port driver, usually implemented as a DLL that provides an interface between the port driver and the system.

monolithic driver  A driver that has many different classes of functionality contained in the same driver.

motherboard  See system board.

multifunction device  A piece of hardware that supports multiple, discrete functions, such as audio, mixer, and music, on a single adapter.

N

NDIS  Network Driver Interface Specification. The interface for network drivers used in Windows NT and Windows. NDIS provides transport independence for network vendors because all transport drivers call the NDIS interface to access the network.

nibble mode  An asynchronous, peripheral-to-host channel defined in the IEEE 1284-1944 standard. Provides a channel for the peripheral to send data to the host, which is commonly used as a means of identifying the peripheral.

NMI  Nonmaskable Interrupt. An interrupt that cannot be overruled by another service request. A hardware interrupt is called nonmaskable if it cannot be masked by the processor’s interrupt enable flag.

NTFS  Windows NT file system. An advanced file system designed for use specifically with the Windows NT operating system. NTFS supports file system recovery and extremely large storage media, in addition to other advantages.

O

OEM  Original equipment manufacturer. Used primarily to refer to systems manufacturers.

OnNow A design initiative that seeks to create all the components required for a comprehensive, system-wide approach to system and device power control. OnNow is a term for a system that is always on but appears off and that responds immediately to user or other requests.

option ROM  Optional read-only memory found on an expansion card. Option ROMs usually contain additional firmware required to properly boot the peripheral connected to the expansion card, for example, a hard drive.

P

PCI  Peripheral Component Interconnect. A 32-bit or 64-bit bus designed to be used with devices that have high bandwidth requirements, such as the display subsystem.

planar  See system board.

Plug and Play  A design philosophy and set of specifications that describe hardware and software changes to the system and its peripherals that automatically identify and arbitrate resource requirements among all devices and buses on the system. Plug and Play specifies a set of device driver interface elements that are used in addition to, not in place of, existing driver architectures.

port  A connection or socket used to connect a device—such as a printer, monitor, or modem— to the computer. Information is sent from the computer to the device through a cable.

port driver  A low-level driver that responds to a set of system-defined device control requests and possibly to an additional set of driver-defined (private) device control requests sent down by a corresponding class driver. A port driver insulates class drivers from the specifics of host bus adapters and synchronizes operations for all its class drivers.

port replicator  Low-cost docking-station substitute intended to provide convenient, one-step connection to multiple desktop devices.

POST  Power-on self-test. A procedure of the system BIOS that identifies, tests, and configures the system in preparation for loading the operating system.

power management  Mechanisms in software and hardware to minimize system power consumption, manage system thermal limits, and maximize system battery life. Power management involves trade-offs among system speed, noise, battery life, processing speed, and power consumption.

Q

QIC Quarter-Inch Cartridge Drive Standards, Inc. An international trade association dedicated to promoting use of quarter-inch tape technology and products. For more information, visit the web site at http://www.qic.org/.

R

RAM Random access memory. Semiconductor-based memory that can be read and written by the microprocessor or other hardware devices. Refers to volatile memory, which can be written as well as read.

real-time processing  Processing that supports

real-time functions such as telephony.

registry  In Windows NT and Windows, the tree-structured hierarchical database where general system hardware and software settings are stored. The registry supersedes the use of separate INI files for all system components and applications that know how to store values in the registry.

resource 1. A set from which a subset can be allocated for use by a client, such as memory or bus bandwidth. This is not the same as resources that are allocated by Plug and Play. 2. A general term that refers to IRQ signals, DMA channels, I/O port addresses, and memory addresses for Plug and Play.

RISC  Reduced instruction set computing. A type of microprocessor design that focuses on rapid and efficient processing of a relatively small set of instructions. RISC architecture limits the number of instructions that are built into the microprocessor, but optimizes each so it can be carried out very rapidly—usually within a single clock cycle.

RISC-based  Refers to computers based on Windows NT–compatible implementations of RISC processors (specifically DEC Alpha).

rt  Real time. In computing, refers to an operating mode under which data is received and processed; the results are returned instantaneously.

S

scalability  1. Ability of a system to take advantage of multiple processors. 2. The ability to vary the information content of a program by changing the amount of data that is stored, transmitted, or displayed. 3. In a video image, this translates to creating larger or smaller windows of video on screen (shrinking effect).

SCSI  Small computer system interface. Pronounced “scuzzy.” An I/O bus designed as a method for connecting several classes of peripherals to a host system without requiring modifications to generic hardware and software.

smart card  A small electronic device about the size of a credit card that contains an embedded integrated circuit. Smart cards are used for a variety of purposes, including storing medical records, storing digital cash, and generating network IDs.

software device  A filter in kernel streaming and ActiveMovie that has no underlying hardware associated with it.

spin down  A power-management capability in which a hard drive shuts down its spindle motor.

static resources  Device resources, such as IRQ signals, DMA channels, I/O port addresses, and memory addresses, that cannot be configured or relocated.

stream  An object representing an entity on an adapter capable of receiving, processing, or supplying data. Notice that a stream is identical to a WDM Stream architecture pin. A stream can accept data from or supply data to the processor, such as a stream representing an MPEG input, or can simply route data through hardware, such as a stream representing an NTSC output jack on the back of an adapter. The purpose of representing non-data hardware with a stream is that the properties of the hardware can be controlled by software.

SVGA  Super VGA. A video standard established by VESA to provide high-resolution color display on IBM-compatible computers.

system board  Also motherboard or planar. The primary circuit board in a system that contains most of the basic components of the system.

system devices  Devices on the system board, such as interrupt controllers, keyboard controller, real-time clock, DMA page registers, DMA controllers, memory controllers, FDC, ATA ports, serial and parallel ports, PCI bridges, and so on. In today’s systems, these devices are typically integrated in the supporting chip set.

T

TAPI  Telephony Application Program Interface. A set of Win32-based calls that applications use to control modems and telephones by routing application function calls to the appropriate service provider DLL for a modem.

TCP/IP Transport control protocol/interface program. A software protocol developed by the Department of Defense for communications between computers.

telephony  Telephone technology.

U

UART  Universal Asynchronous Receiver/ Transmitter. A module composed of a circuit that contains both the receiving and transmitting circuits required for asynchronous serial communication.

Unimodem  Universal modem driver. A driver-level component that uses modem description files to control its interaction with the communications driver, VCOMM.

UPS  Uninterruptible power supply. A device connected between a computer and a power source that ensures that electrical flow to the computer is not interrupted because of a blackout and, in most cases, protects the computer against potentially damaging events such as power surges and brownouts.

USB  Universal Serial Bus. A bi-directional, isochronous, dynamically attachable serial interface for adding peripheral devices such as game controllers, serial and parallel ports, and input devices on a single bus.

USB class  The class of filters under WDM that provides a bus interface and bus enumerator for USB.

user mode  The nonprivileged processor mode in which application code executes, including protected subsystem code in Windows NT.

user-mode drivers  Win32-based multimedia drivers and VDDs for MS-DOS–based applications with application-dedicated devices. For information, see the Multimedia Drivers and Virtual DOS Drivers documentation in the Windows NT DDK.

V

VAR  Value added reseller. A company that resells hardware and software packages to developers and/or end users.

VESA  Video Electronics Standards Association. A governing body that establishes standards for the video and graphics portions of the electronics industry.

W

WAN  Wide area network. A communications network that connects geographically separated areas. Compare with LAN.

WBEM  Web-based Enterprise Management. A DMTF initiative to provide a standards-based mechanism to specify information exchange between management applications and managed components.  This work was recently transferred to the DMTF by  BMC Software, Inc., Cisco Systems, Inc., Compaq Computer Corporation, Intel Corporation, and Microsoft Corporation.

WDL  Windows NT Driver Library. See WHQL.

WDM  Windows Driver Model. A 32-bit driver model based on the Windows NT driver model that is designed to provide a common architecture of I/O services and binary-compatible device drivers for both Windows NT and Windows operating systems for specific classes of drivers. These driver classes include USB and IEEE 1394 buses, audio, still-image capture, video capture, and HID-compliant devices such as USB mice, keyboards, and joysticks. Provides a model for writing kernel-mode drivers and minidrivers, and provides extensions for Plug and Play and power management.

WHQL  Windows Hardware Quality Labs. Provides testing services for hardware and drivers for Windows and Windows NT. Administers testing for the “Designed for Microsoft Windows” logo programs. See http://www.microsoft.com/hwtest/.

Win32 API  A 32-bit application programming interface for both Windows and Windows NT that includes sophisticated operating system capabilities, security, and API routines for Windows-based applications.

Windows Management Instrumentation Extensions to WDM developed for Windows NT 5.0 and Windows to provide an operating system interface through which instrumented components can provide information and notifications.

Windows NT The Microsoft Windows NT version 5.0 operating system, including any add-on capabilities and later versions of the operating system.

Windows NT DDK  Supports Windows NT, provided through MSDN Professional membership. Documents the Windows NT driver model (upon which WDM is based) and is an essential component for building WDM drivers.

Z

Zero Administration for Windows  An initiative that focuses on improving Windows and Windows NT for maximum automation of administrative tasks with centralized control and maximum flexibility.