Athlon Motherboard Roundup - March 2000

If you remember back to our initial review of the Athlon processor, you will remember that one of the benefits of the Athlon’s EV6 bus protocol is that it is ideal for a multiprocessing environment. 

Intel's GTL+ Shared Bus

The reason it is ideal for this type of an environment is because EV6 is a point to point bus protocol unlike the Pentium III’s GTL+ which is a shared bus.  The way the Pentium III’s GTL+ bus works is that each processor shares the 100/133MHz pathway (or system bus) to the North Bridge.  Assuming that we’re talking about one of the new 133MHz FSB Pentium IIIs, then the system bus can handle 1.06GB/s of data transfers at any given time.  If we have two processors in that system, then the 1.06GB/s of bandwidth is split among the two.  If we have four processors, the 1.06GB/s is split between the four and so on and so forth.

Digital/AMD's EV6 Point-to-Point Bus

With a point to point bus like the Athlon’s EV6, each processor in the system receives its own connection to the North Bridge.  For example, the current EV6 implementation for the Athlon runs at 100MHz DDR, offering an effective 1.6GB/s of available bandwidth to/from the North Bridge.  Adding a second processor into the system leaves each CPU with 1.6GB/s of bandwidth, and adding a fourth still allows each CPU that same 1.6GB/s of bandwidth between itself and the North Bridge.  As you can see, there is much more room for expandability and multiprocessor support with the Athlon’s EV6 bus.

Unfortunately, there is currently no chipset support for it and when the chipset support does come around (end of this year/beginning of next year) you can expect motherboard designs to be a bit on the expensive side.  Instead of sharing a single connection to the North Bridge, motherboard manufacturers will now have to worry about providing two connections to the North Bridge, which should make designs much more complex than they already are. 

There will be multiprocessor support for the Athlon -- it’s inevitable-- but don’t expect to see it in this motherboard roundup or any roundups in the very near future.