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Bob Sarah wrote: > > So how is it done and is this what is > meant by context switching? Context switching is when the CPU switches from one process to another. The overhead of this is often important in deciding on implementation issues. Linux has a very low overhead for context switching, this also had some effects on how they implemented the handling of threads. > What are Posix threads? POSIX is the Portable Operating System standards, a standard body of the US government I believe. They have been steadily defining and refining various programming API's, and related software interfaces, for many years. For example "bash" is based largely on the Posix shell standard. Many Linux/Unix manual pages will list Posix conformance where it applies (see "man fork" for example). Some people tend to talk of POSIX compliance as if it were one standard, but it clearly isn't, for example Windows NT has a POSIX subsystem (Required to sell IT stuff to parts of the US Federal Government), but it doesn't as far as I know ship with a POSIX compliant shell. I guess if you see conforming to the minimal standards required to sell to the US Federal Government as a hurdle, then you could end up refering to meeting this requirement as "POSIX compliant". "POSIX threads" refers to a thread library implementation conforming to their standards. The thread standards have been out long enough for most UNIX flavours to have conforming implementations, although as always with big standards, there is sometimes still the odd discrepancy in implementation. I'll let others with more formal qualifications in computing answer your other questions. -- Are you using the Internet to best effect ? www.eighth-layer.com Tel: +44(0)1395 232769 ICQ: 116952768 Moderated discussion of teleworking at news:uk.business.telework -- The Mailing List for the Devon & Cornwall LUG Mail majordomo@xxxxxxxxxxxx with "unsubscribe list" in the message body to unsubscribe.