sharing a single bus. Double- and triple-width option modules are used to mechanically accommodate larger option modules and for supplying more power. The mechanical specification for option modules is also flexible. There are few limitations for attaching daughterboards such SIMM modules (used in graphics options) and components can be mounted on both sides of the option module, with components on the bottom being restricted only in height to ensure that the option module could fit in the system module while maintaining enough airflow for cooling. An airflow of 150 LFMs is required above the option module and an airflow of 50 LFMs is required below the option module. Each slot has 44 signal pins, of which 32 are used for data and addressing. Electrical The TURBOchannel slot supplies +5 and +12V power rails and provides a maximum of 26 watts of power. The following table shows how many amperes are supplied by each power rail. TURBOchannel Extender The TURBOchannel bus can be "extended" by the TURBOchannel Extender (TcE) box. Because some options such as 3D graphics accelerators may require more power and board space than a single slot can provide, they are often double- or triple-width option modules. As such option modules consume additional space and slots inside a system, their presence may limit the number or even prevent the installation of other TURBOchannel option modules. A TURBOchannel Extender box is used to reduce the number of slots required inside a system for double and triple width options. The TURBOchannel Extender box contains a PCB with three TURBOchannel slots and a power supply for supplying the required power to the slots. A TURBOchannel option module, for installation in the host, accompanies the TcE box. It has an external cable that connects to the TcE box. What the option module is doing is bringing out the data, addressing and control lines to the TURBOchannel extender box. There is no performance loss associated with the use of a TcE box, although TcE boxes support only one option module regardless of how many remaining slots there are. See also List of device bandwidths References TURBOchannel Hardware Specification, EK-369AA-OD-007B, January 1993, Digital Equipment Corporation. External links A collection of archived documents from the defunct TURBOchannel Industry Group. Contains the entire TURBOchannel specification. Shows interior of a computer using the TURBOchannel bus Advanced RISC Computing Computer buses DEC hardware