The term Legacy Plug and Play, also shortened to Legacy PnP, describes a series of specifications and

Microsoft Windows Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...

features geared towards operating system configuration of devices, and some device IDs are assigned by

UEFI Forum UEFI Forum, Inc. is an Business alliance, alliance between technology companies to coordinate the development of the UEFI specifications. The board of directors includes representatives from twelve ''promoter'' companies: Advanced Micro Devices, ...

. The standards were primarily aimed at the

IBM PC The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first microcomputer released in the List of IBM Personal Computer models, IBM PC model line and the basis for the IBM PC compatible ''de facto'' standard. Released on ...

standard bus, later dubbed Industry Standard Architecture (ISA). Related specifications are also defined for the common external or specialist buses commonly attached via ISA at the time of development, including

RS-232 In telecommunications, RS-232 or Recommended Standard 232 is a standard introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' (''data terminal equipment'') such as a compu ...

and

parallel port In computing, a parallel port is a type of interface found on early computers ( personal and otherwise) for connecting peripherals. The name refers to the way the data is sent; parallel ports send multiple bits of data at once (paralle ...

devices. As a Windows feature, Plug and Play refers to operating system functionality that supports connectivity, configuration and management with native plug and play devices. Originally considered part of the same feature set as the specifications, Plug and Play in this context refers primarily to the responsibilities and interfaces associated with Windows driver development. Plug and Play allows for detection of devices without user intervention, and occasionally for minor configuration of device resources, such as I/O ports and device memory maps. PnP is a specific set of standards, not be confused with the generic term plug and play, which describes any hardware specification that alleviates the need for user configuration of device resources.

ACPI Advanced Configuration and Power Interface (ACPI) is an open standard that operating systems can use to discover and configure computer hardware components, to perform power management (e.g. putting unused hardware components to sleep), auto con ...

is the successor to Legacy Plug and Play.

Overview

The Plug and Play standard requires configuration of devices to be handled by the PnP BIOS, which then provides details of resources allocations to the operating system. The process is invoked at boot time. When the computer is first turned on, compatible devices are identified and assigned non-conflicting IO addresses,

interrupt request In a computer, an interrupt request (or IRQ) is a hardware signal sent to the processor that temporarily stops a running program and allows a special program, an interrupt handler, to run instead. Hardware interrupts are used to handle events s ...

numbers and DMA channels. The term was adopted by Microsoft in reference to their

Windows 95 Windows 95 is a consumer-oriented operating system developed by Microsoft and the first of its Windows 9x family of operating systems, released to manufacturing on July 14, 1995, and generally to retail on August 24, 1995. Windows 95 merged ...

product. Other

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

s, such as

AmigaOS AmigaOS is a family of proprietary native operating systems of the Amiga and AmigaOne personal computers. It was developed first by Commodore International and introduced with the launch of the first Amiga, the Amiga 1000, in 1985. Early versions ...

Autoconfig Autoconfig is an auto-configuration protocol of Amiga computers which is intended to automatically assign resources to expansion devices without the need for jumper settings. It is analogous to PCI configuration through ACPI. Autoconfig is in ...

and the

Mac OS Mac operating systems were developed by Apple Inc. in a succession of two major series. In 1984, Apple debuted the operating system that is now known as the classic Mac OS with its release of the original Macintosh System Software. The system ...

NuBus system, had already supported such features for some time (under various names, or no name). Even

Yggdrasil Linux Yggdrasil Linux/GNU/X, or LGX (pronounced ''igg-drah-sill''), is an early Linux distribution developed by Yggdrasil Computing, Incorporated, a company founded by Adam J. Richter in Berkeley, California. Yggdrasil was the first company to create ...

advertised itself as "Plug and Play Linux" at least two years before Windows 95. But the term ''

plug and play In computing, a plug and play (PnP) device or computer bus is one with a specification that facilitates the recognition of a hardware component in a system without the need for physical device configuration or user intervention in resolving reso ...

'' gradually became universal due to worldwide acceptance of Windows. Typically, non-PnP devices need to be identified in the computer's BIOS setup so that the PnP system will not assign other devices the resources in use by the non-PnP devices. Problems in the interactions between legacy non-PnP devices and the PnP system can cause it to fail, leading to this technology having historically been referred to as "plug and pray".

Specifications

Legacy Plug and Play Specification was defined by

Microsoft Microsoft Corporation is an American multinational corporation and technology company, technology conglomerate headquartered in Redmond, Washington. Founded in 1975, the company became influential in the History of personal computers#The ear ...

and

Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California, and Delaware General Corporation Law, incorporated in Delaware. Intel designs, manufactures, and sells computer compo ...

, which proposed changes to legacy hardware, as well as the

BIOS In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is a type of firmware used to provide runtime services for operating systems and programs and to perform hardware initialization d ...

to support operating system-bound discovery of devices. These roles were later assumed by the

standard, which also moves support for power management and configuration into the operating system, as opposed to the firmware as previously required by the "Plug and Play BIOS" and

APM APM, apm, or Apm may refer to: Technology Computer technology *Active policy management, a discipline within enterprise software *Advanced Power Management, a legacy technology in personal computers * Apple Partition Map, computer disk partiti ...

specifications. The following standards compose what Microsoft describe as Legacy Plug and Play, as opposed to native Plug-and-Play specifications such as

PCI PCI may refer to: Business and economics * Payment card industry, businesses associated with debit, credit, and other payment cards ** Payment Card Industry Data Security Standard, a set of security requirements for credit card processors * Prov ...

and

USB Universal Serial Bus (USB) is an industry standard, developed by USB Implementers Forum (USB-IF), for digital data transmission and power delivery between many types of electronics. It specifies the architecture, in particular the physical ...

. *Plug and Play BIOS Specification *Plug and Play ISA Specification *Plug and Play Design Specification for IEEE 1394 *Plug and Play External COM Device Specification *Plug and Play Parallel Port Device Specification *Plug and Play ATA Specification *Plug and Play SCSI Specification *Legacy Plug and Play Guidelines

Windows Vista Windows Vista is a major release of the Windows NT operating system developed by Microsoft. It was the direct successor to Windows XP, released five years earlier, which was then the longest time span between successive releases of Microsoft W ...

requires an ACPI-compliant BIOS, and the ISAPnP is disabled by default.

Requirements

To use Plug and Play, three requirements have to be met: #The OS must be compatible with Plug and Play. #The

must support Plug and Play. #The device to be installed must be a Plug and Play compliant device.

Hardware identification

Plug-and-play hardware typically also requires some sort of ID code that it can supply, in order for the computer software to correctly identify it. The Plug-and-play ID can have two form: 3-byte manufacturer ID plus 2-byte hex number (e.g. PNP0A08), or 4-byte manufacturer ID plus 2-byte hex number (e.g. MSFT0101). In addition, a PnP device may have Class Code and Subsystem ID. This ID code system was not integrated into the early

Industry Standard Architecture Industry Standard Architecture (ISA) is the 16-bit internal bus (computing), bus of IBM PC/AT and similar computers based on the Intel 80286 and its immediate successors during the 1980s. The bus was (largely) backward compatible with the 8-bi ...

(ISA) hardware common in PCs when Plug and Play was first introduced. ISA Plug and Play caused some of the greatest difficulties that made PnP initially very unreliable. This led to the derisive term "Plug and Pray", since I/O addresses and IRQ lines were often set incorrectly in the early days. Later

computer bus In computer architecture, a bus (historically also called a data highway or databus) is a communication system that transfers data between components inside a computer or between computers. It encompasses both hardware (e.g., wires, optical ...

es like MCA, EISA and

(which was becoming the industry standard at that time) integrated this functionality. Finally, the

of the computer needs to be able to handle these changes. Typically, this means looking for

interrupt In digital computers, an interrupt (sometimes referred to as a trap) is a request for the processor to ''interrupt'' currently executing code (when permitted), so that the event can be processed in a timely manner. If the request is accepted ...

s from the bus saying that the configuration has changed, and then reading the information from the bus to locate what happened. Older bus designs often required the entire system to be read in order to locate these changes, which can be time-consuming for many devices. More modern designs use some sort of system to either reduce or eliminate this "hunt"; for example, USB uses a hub system for this purpose. When the change is located, the OS then examines the information in the device to figure out what it is. It then has to load up the appropriate

device driver In the context of an operating system, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton. A driver provides a software interface to hardware devices, enabli ...

s in order to make it work. In the past, this was an all-or-nothing affair, but modern operating systems often include the ability to find the proper driver on the

Internet The Internet (or internet) is the Global network, global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a internetworking, network of networks ...

and install it automatically.

References

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External links