The devices connected to PCI-bus are configured automatically – due to the Plug and Play conception. Thus, any PCI device is automatically determined, receives interruption, address space in memory and other. There is only one disadvantage: you should turn off the computer power supply to replace, delete or add a device. But nowadays there is the mechanism that enables to replace PCI devices without turning off the power supply.
Both the allocation of interruptions and direct access to memory are executed by using special services that provide compatibility with operating modes of ISA-bus. A regular direct access of PCI-device to the memory is impossible this device already has a mechanism “bus master”. This causes the occurrence of parameters in BIOS that either enable to switch on or off the deprecated functions or that set the time delays.
The parameter “PCI 2.1 Support” (PCI 2.1 Compliance) enables to switch on/off the support of PCI 2.1 specification. This parameter has got two values: Enabled and Disabled. 2.0 specification has got two main differences from 2.0 specification: a maximum clock frequency of a bus is increased to 66 MHz, and there is also a mechanism of PCI-PCI bridge that enables to lift the restrictions of 2.0 specification, due to which no more than four devices are enabled to be set on a bus. This parameter should be switched on because a lot of manufacturers of motherboards use 2.2 specification with various functions of energy management, fast connection of peripherals, the support of 64-bit data transmission on the 66 MHz frequency and other. This parameter should be switched off (Disabled value) only if you use the outdated PCI-devices. But it is not recommended to use new and old motherboards simultaneously because disconnection of 2.1 specification support may affect the productivity of a new device.