It allows up to 15 intelligent devices to share a single bus, with the slowest device participating in the control and data transfer handshakes to drive the speed of the transaction. The maximum data rate is about one megabit per second.
Other standards committees have adopted HP-IB (American Standards Institute with ANSI Standard MC 1.1 and International Electro-technical Commission with IEC Publication 625-1).
To paraphrase from the HP 1989 Test & Measurement Catalog (the 50th Anniversary version): The HP-IB has a party-line structure wherein all devices on the bus are connected in parallel. The 16 signal lines within the passive interconnecting HP-IB (IEEE-488) cable are grouped into three clusters according to their functions (Data Bus, Data Byte Transfer Control Bus, General Interface Management Bus).
In June 1987 the IEEE approved a new standard for programmable instruments called IEEE Std. 488.2-1987 Codes, Formats, Protocols, and Common Commands. It works with the IEEE Standard Digital Interface for Programmable Instrumentation, IEEE 488-1978 (now 488.1). HP-IB is Hewlett-Packard's implementation of IEEE 488.1.
It was used by computers such as the Commodore PET.
See also: Hewlett-Packard Interface Bus
National Instruments link : http://zone.ni.com/devzone/conceptd.nsf/webmain/1DF3ADFEBDFB9F77862567C300782C11?opendocument&node=DZ52341_US