What's UP With [I.sub.2]O SIG? - News Briefs

Computer Technology Review, Oct, 1999 by Roger Cummings

Work started on the initial [I.sub.2]O specification in 1995, the product of a strategic discussion between engineers at Intel and Netframe Systems. The majority of the technical work on [I.sub.2]O was done in 1996 and 1997, when several plugfests were held where developers from the U.S., Europe, and Asia met to test hardware and software prototypes. Revision 1.5 of the specification was released in 1997, made public in 1998, and over 500 developers registered on the [I.sub.2]O SIG web site to receive a copy.

The [I.sub.2]O specification defines a "grand architecture" for servers in which one or more I/O Processors (IOPs) are provided, which are separate from the main server CPU. These IOPs control interfaces, which are mounted on the motherboard or implemented as plug-in cards. A queued message-based protocol for CPU to IOP communication is included, with a common packet format, flexible scatter/gather facilities, and dynamic configuration support. Specific message classes are defined to communicate with abstractions of block storage devices, SCSI peripherals, LAN interfaces, etc., and between peer IOPs.

As a result of experience with products based on Rev 1.5, further development work was conducted in 1998, which led to Revision 2.0 of the specification being announced in May 1999 and which will shortly be released to developers. New features included in 2.0 are replacement scatter/gather list formats, support for 64-bit physical addressing and message buffering in host memory, and a message class for communication with hot-plug controllers.

The complete [I.sub.2]O "grand architecture" is not found in many servers. However, the protocol, abstraction scheme, and message classes defined to support the architecture have been successfully used in a number of shipping products. The majority of the shipping [I.sub.2]O products use PCI as the transport mechanism for [I.sub.2]O messages. It should be noted, however, that the [I.sub.2]O architecture does not require the use of PCI, or even shared memory, between the IOP and CPU. Hence, the [I.sub.2]O API is also finding considerable use in the "switched fabric" interconnection schemes currently under development.

Roger Cummings is the director of strategic relationships at DPT (Maitland, FL).

www.dpt.com

www.i2sig.org