ISA Bus. Part I

ISA-devices are hardly used in modern computers, that’s why most manufacturers do not equip their motherboards with these slots. Nevertheless, some time ago ISA-devices were very popular.

In contrast to PCI-bus with several master-devices on it, ISA-bus may have only one master-device. Use the parameter “Bus Mastering” to permit the use of this device in the mode “bus master”. This parameter may have two values: Enabled and Disabled. If the value “Disabled” is set, no one device connected to ISA-bus could operate as dial with it.

Most parameters in BIOS, related to ISA-bus setting, enable to control various delays resulting from the slowness of ISA-bus against the rest components, for example PCI-bus.

Thus, the parameter “16 Bit ISA I/O Command WS” (ISA 16 Bit I/O Wait States) enables to compensate the difference between the operating speed of system devices and computer peripherals. Such compensation is compulsory, for example, the additional waiting time or respond from a device were not identified. If there is no preset delay, a signal about device capacity may fail and your system will automatically assume it as a nonfunctional device. This parameter may have two values: Enabled and Disabled. If the usage of delay is enabled, the system sets it automatically. Some types of BIOS offer the direct identification of a number of wait states. The best speed is achieved without any delays (the value “Disabled” or 0) but this may cause failures in operation of ISA-devices. If there are no expansion cards of ISA in your computer, this parameter should be turned off.