Editing Plug and play (section)

== Legacy Plug and Play ==
{{Main|Legacy Plug and Play}}
In 1995, Microsoft released [[Windows 95]], which tried to automate device detection and configuration as much as possible, but could still fall back to manual settings if necessary. During the initial install process of Windows 95, it would attempt to automatically detect all devices installed in the system. Since full auto-detection of everything was a new process without full industry support, the detection process constantly wrote to a progress tracking log file during the detection process. In the event that device probing would fail and the system would freeze, the end-user could reboot the computer, restart the detection process, and the installer would use the tracking log to skip past the point that caused the previous freeze.<ref>Scott Mueller, ''Upgrading and Repairing PCs, Eleventh Edition'', Que, 2999, {{ISBN|0-7897-1903-7}}, page 1370</ref>

At the time, there could be a mix of devices in a system, some capable of automatic configuration, and some still using fully manual settings via jumpers and DIP switches. The old world of DOS still lurked underneath Windows 95, and systems could be configured to load devices in three different ways:
* through Windows 95 Device Manager drivers only
* using DOS drivers loaded in the CONFIG.SYS and AUTOEXEC.BAT configuration files
* using a combination of DOS drivers and Windows 95 Device Manager drivers

Microsoft could not assert full control over all device settings, so configuration files could include a mix of driver entries inserted by the Windows 95 automatic configuration process, and could also include driver entries inserted or modified manually by the computer users themselves. The Windows 95 Device Manager also could offer users a choice of several semi-automatic configurations to try to free up resources for devices that still needed manual configuration.

[[File:Kouwell KW-524J - 8-bit PC ISA interface card - 4 port - 2 serial - 2 parallel.jpg|thumb|An example of an ISA interface card with extremely limited interrupt selection options, a common problem on PC ISA interfaces.<br>Kouwell KW-524J dual serial, dual parallel port, 8-bit ISA, manufactured in 1992:<br>* Serial 1: IRQ 3/4/9<br>* Serial 2: IRQ 3/4/9<br>* Parallel 1: IRQ 5/7<br>* Parallel 2: IRQ 5/7<br>(There is no technical reason why 3,4,5,7,9 cannot all be selectable choices for each port.)]]
Also, although some later ISA devices were capable of automatic configuration, it was common for PC ISA expansion cards to limit themselves to a very small number of choices for interrupt request lines. For example, a network interface might limit itself to only interrupts 3, 7, and 10, while a sound card might limit itself to interrupts 5, 7, and 12. This results in few configuration choices if some of those interrupts are already used by some other device.

The hardware of PC computers additionally limited device expansion options because interrupts could not be shared, and some multifunction expansion cards would use multiple interrupts for different card functions, such as a dual-port serial card requiring a separate interrupt for each serial port.

Because of this complex operating environment, the autodetection process sometimes produced incorrect results, especially in systems with large numbers of expansion devices.  This led to device conflicts within Windows 95, resulting in devices which were supposed to be fully self-configuring failing to work. The unreliability of the device installation process led to Plug and Play being sometimes referred to as ''Plug and Pray''.<ref>{{cite web
|url=https://www.techspot.com/community/topics/plug-and-play-overview-how-windows-finds-drivers-for-usb-devices.127886
|title=Plug and Play Overview: How Windows Finds Drivers for USB Devices
|quote=So Plug and Play sounds great, right? Well, it is... when everything works right (which is why it's sometimes also called "Plug and Pray"!) |date=May 20, 2009}}</ref>

Until approximately 2000, PC computers could still be purchased with a mix of ISA and PCI slots, so it was still possible that manual ISA device configuration might be necessary. But with successive releases of new operating systems like Windows 2000 and Windows XP, Microsoft had sufficient clout to say that drivers would no longer be provided for older devices that did not support auto-detection. In some cases, the user was forced to purchase new expansion devices or a whole new system to support the next operating system release.