What is the future for PC/104?

The PC99 specification recently released by Intel and Microsoft has left many engineers wondering if the days of the venerable PC/104 interface are numbered.

The PC/104+ standard was introduced in 1996 by the PC/104 Consortium, adding a PCIbus to the existing ISAbus found on PC/104 boards, and enabling higher performance processors to be used in embedded applications.

The PC/104+ standard was readily accepted because of its (arguably) most endearing feature: full compatibility with PC/104.

For example, Sensoray's model 322 CRT/LCD adapter implements a "pure" PC/104+ interface, but it also includes an integrated PC/104 pass-through connector so that PC/104 boards may be freely inserted anywhere in the stack.

Since the introduction of the PC/104+ standard, PC/104 boards have lived in harmony with PC/104+ boards in countless embedded systems.

More recently, the PC99 specification released by Intel and Microsoft has left many engineers wondering if the days of the venerable PC/104 interface are numbered.

The specification would seem to make the ISAbus, and by association, the PC/104bus, relics of the past.

This is a matter of great interest to engineers because the imminent demise of PC/104 would force many designers to abandon their foundational PC/104 IP and switch to "pure" PC/104+ platforms for new designs.

In a variation of Mark Twain's famous quip: "rumours of the death of PC/104 have been greatly exaggerated".

The majority of today's PC/104 modules are still based on the workhorse ISAbus, with a steady stream of new products being released for both the PC/104 and PC/104+ interface.

This trend will continue for the foreseeable future because PC/104 boards are fully compatible with PC/104+ stacks, and just as important, PC/104 boards often cost less and are simpler and more reliable than pure PC/104+ solutions.

And despite the popularity of the PCIbus and the impending extinction of ISA on desktop PCs, embedded PC/104+ systems continue to liberally use both bus types: PCI for high speed transfers (eg video and storage applications), and ISA for applications that don't require the higher bandwidth, such as analogue I/O, digital I/O, machine control etc.

It is likely that the PC/104+ bus will gain favour with developers as technologies progress and needs change, but the large number of currently available PC/104 products and the industry's willingness to continue to support this technology clearly indicate that PC/104 is here to stay.

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