ISA Plug and Play
Encyclopedia
The term Legacy Plug and Play, also shortened to PnP, describes a series of specifications and Microsoft Windows
features geared towards operating system configuration of devices. The standards were primarily aimed at pre-existing hardware that did not support Plug and Play, most predominately the IBM PC
standard bus, later dubbed ISA
. Related specifications are also defined for the common external or specialist busses commonly attached via ISA at the time of development, including RS-232
and LPT
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.
The term Plug and Play was first used by Microsoft in reference to their Windows 95
product. Other operating system
s such as AmigaOS
Autoconfig
and Mac OS
NuBus
system, had already supported such features for some time (under various names, or no name), but the term plug and play gradually became universal due to worldwide acceptance of Windows.
Typically, non-PnP devices need to be identified in the computer's BIOS setup screen so that the PnP system will not re-assign those 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"
to support operating system-bound discovery of devices. These roles were later assumed by the ACPI
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
specifications. The following standards compose what Microsoft describe as Legacy Plug and Play, as opposed to native Plug-and-Play specifications such as PCI and USB.
Apart from the Plug and Play BIOS Specification, all standards are still supported by Microsoft. However, support for them as opposed to Advanced Configuration and Power Interface
will be removed in future version of Windows.
This ID code system was not integrated into the early Industry Standard Architecture
(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
es like MCA
, EISA
and PCI
(which was becoming the industry standard at that time) integrated this functionality.
Finally, the operating system
of the computer needs to be able to handle these changes. Typically this means looking for interrupt
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 lots of 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
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
and install it automatically.
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
features geared towards operating system configuration of devices. The standards were primarily aimed at pre-existing hardware that did not support Plug and Play, most predominately the IBM PC
IBM PC
The IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform. It is IBM model number 5150, and was introduced on August 12, 1981...
standard bus, later dubbed ISA
Industry Standard Architecture
Industry Standard Architecture is a computer bus standard for IBM PC compatible computers introduced with the IBM Personal Computer to support its Intel 8088 microprocessor's 8-bit external data bus and extended to 16 bits for the IBM Personal Computer/AT's Intel 80286 processor...
. Related specifications are also defined for the common external or specialist busses commonly attached via ISA at the time of development, including RS-232
RS-232
In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
and LPT
LPT
LPT is the original, and still common, name of the parallel port interface on IBM PC-compatible computers. It was designed to operate a text printer that used IBM's 8-bit extended ASCII character set. The name derives from the fact that "line printer" was a common generic term at the time for any...
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.
Overview
The Plug and Play standard requires configuration of devices to be handled by system firmware, 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 addresses and IRQ numbers.The term Plug and Play was first used by Microsoft in reference to their Windows 95
Windows 95
Windows 95 is a consumer-oriented graphical user interface-based operating system. It was released on August 24, 1995 by Microsoft, and was a significant progression from the company's previous Windows products...
product. Other operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
s such as AmigaOS
AmigaOS
AmigaOS is the default native operating system of the Amiga personal computer. It was developed first by Commodore International, and initially introduced in 1985 with the Amiga 1000...
Autoconfig
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...
and Mac OS
Mac OS
Mac OS is a series of graphical user interface-based operating systems developed by Apple Inc. for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface...
NuBus
NuBus
NuBus is a 32-bit parallel computer bus, originally developed at MIT as a part of the NuMachine workstation project. The first complete implementation of the NuBus and the NuMachine was done by Western Digital for their NuMachine, and for the Lisp Machines Inc. LMI-Lambda. The NuBus was later...
system, had already supported such features for some time (under various names, or no name), but the term plug and play gradually became universal due to worldwide acceptance of Windows.
Typically, non-PnP devices need to be identified in the computer's BIOS setup screen so that the PnP system will not re-assign those 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 was defined in Microsoft and Intel specifications, which proposed changes to legacy hardware, as well as the BIOSBIOS
In IBM PC compatible computers, the basic input/output system , also known as the System BIOS or ROM BIOS , is a de facto standard defining a firmware interface....
to support operating system-bound discovery of devices. These roles were later assumed by the ACPI
Advanced Configuration and Power Interface
In computing, the Advanced Configuration and Power Interface specification provides an open standard for device configuration and power management by the operating system....
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
Advanced Power Management
Advanced power management is an API developed by Intel and Microsoft and released in 1992 which enables an operating system running an IBM-compatible personal computer to work with the BIOS to achieve power management.Revision 1.2 was the last version of the APM specification, released in 1996....
specifications. The following standards compose what Microsoft describe as Legacy Plug and Play, as opposed to native Plug-and-Play specifications such as PCI and USB.
- 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 SCSI Specification
- Legacy Plug and Play Guidelines
Apart from the Plug and Play BIOS Specification, all standards are still supported by Microsoft. However, support for them as opposed to Advanced Configuration and Power Interface
Advanced Configuration and Power Interface
In computing, the Advanced Configuration and Power Interface specification provides an open standard for device configuration and power management by the operating system....
will be removed in future version of Windows.
Requirements
A PnP-compatible computer must meet three requirements:- The OSOperating systemAn operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
must be PnP-compatible. - The BIOSBIOSIn IBM PC compatible computers, the basic input/output system , also known as the System BIOS or ROM BIOS , is a de facto standard defining a firmware interface....
must support PnP. - The device to be installed must be a PnP 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.This ID code system was not integrated into the early Industry Standard Architecture
Industry Standard Architecture
Industry Standard Architecture is a computer bus standard for IBM PC compatible computers introduced with the IBM Personal Computer to support its Intel 8088 microprocessor's 8-bit external data bus and extended to 16 bits for the IBM Personal Computer/AT's Intel 80286 processor...
(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
Computer bus
In computer architecture, a bus is a subsystem that transfers data between components inside a computer, or between computers.Early computer buses were literally parallel electrical wires with multiple connections, but the term is now used for any physical arrangement that provides the same...
es like MCA
Micro Channel architecture
Micro Channel Architecture was a proprietary 16- or 32-bit parallel computer bus introduced by IBM in 1987 which was used on PS/2 and other computers through the mid 1990s.- Background :...
, EISA
Extended Industry Standard Architecture
The Extended Industry Standard Architecture is a bus standard for IBM PC compatible computers...
and PCI
Peripheral Component Interconnect
Conventional PCI is a computer bus for attaching hardware devices in a computer...
(which was becoming the industry standard at that time) integrated this functionality.
Finally, the operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
of the computer needs to be able to handle these changes. Typically this means looking for interrupt
Interrupt
In computing, an interrupt is an asynchronous signal indicating the need for attention or a synchronous event in software indicating the need for a change in execution....
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 lots of 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
Device driver
In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....
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
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
and install it automatically.
See also
- User friendliness
- Extended System Configuration DataExtended System Configuration DataESCD or Extended System Configuration Data is a part of nonvolatile BIOS memory on the motherboard of a personal computer, where information about ISA PnP devices is stored...
(ESCD) - Option ROMOption ROMAn Option ROM typically consists of firmware that is called by the system BIOS. For example, an adapter card that controls a boot device might contain firmware that is used to connect the device to the system once the Option ROM is loaded....
External links
- Microsoft Plug and Play Specifications and Papers
- http://www.microsoft.com/whdc/system/pnppwr/pnp/pnpid.mspx (P&P ID)
- http://www.microsoft.com/whdc/archive/idpnp.mspx
- http://www.microsoft.com/whdc/archive/pnpbiosp.mspx