Computer Interconnect

The Computer Interconnect (usually given as the acronym, CI) is high-speed packetized data networking system from DEC; basically a fairly short-range LAN.

It consists of uni-directional point-point links, all running between an interface on each host (called 'nodes' in the CI system) and a 'coupler'. The network's physical topology is thus a star (an approach pioneered by LCS's Version 1 ring), but electrically and logically, it is a linear bus, like the ethernet. It too uses CSMA for access control to the shared transmission medium, but different in detail from that of the Ethernet.

In addition to processors (mostly VAXen, although there was a CI interface for the KL10), intelligent mass storage controllers (such as the HSC50) could be connected to a CI network; this was a key role in the widely-deployed VAXcluster. Acknowledgements are provided by the hardware; if one is not received, a retransmission can be performed.

Node addresses are 8 bits; so the address space could hold up to 256 nodes. The initial coupler (a passive one) supported up to 16 links. All CI links are duplicated, for robustness. (Later versions used them separately, to double the capacity.) Thus, each host has 4 links to it; two transmit, and two receive.

The links are coaxial cables. Data speeds were 70 megabits per second; link lengths could be up to 45 meters. At the analog level, it used Manchester encoding, on baseband signaling.

See also

• SC008 Star Coupler
• CI20 Computer Interconnect
• CI780 Computer Interconnect Interface
• CI750 Computer Interconnect Interface
• CIBCI VAX Bus Interconnect Computer Interconnect Interface, 1st generation
• CIBCA VAX Bus Interconnect Computer Interconnect Interface, 2nd generation
• CIXCD XMI Computer Interconnect Interface
• CITCA TURBOchannel Computer Interconnect Interface
• CIQBA QBUS Computer Interconnect Interface

External links

• VAXclusters: A Closely-Coupled Distributed System - paper on VAXclusters which describes the CI in some detail