VIA Apollo Pro 133/133A Motherboard Roundup - February 2000

The Apollo Pro 133 and 133A share the same memory controller, which supports two major types of memory: SDRAM and Virtual Channel SDRAM.  Unfortunately absent from this short list is DDR SDRAM, and according to VIA we won’t see support for that until later this year but it will be in the form of a P6-bus motherboard platform, meaning that it will work with the Pentium III. 

The 693A and 694X North Bridges support both PC133 and PC100 SDRAM as well as VC100 and VC133 Virtual Channel SDRAM.  The way the chipset goes about supporting more than one clock frequency of the same memory type is by allowing the user to clock their memory at 33MHz faster or 33MHz slower than their FSB frequency or equal to their FSB frequency if they have memory capable of running at that speed. 

This allows a user with PC100 memory to run their memory at 100MHz while their FSB operates at 133MHz (133MHz – 33MHz = 100MHz) while a user with PC133 memory can run their memory at 133MHz even if their FSB is only running at 100MHz.  There are obviously more combinations than this alone, but it is up to the motherboard  manufacturer to make sure that support for these combinations is provided for. 

Ideally, motherboard manufacturers should allow a user to set his/her memory bus equal to the FSB, FSB + 33MHz or FSB – 33MHz regardless of the FSB setting.  This would give the user the opportunity to theoretically clock their memory at 166MHz while their FSB runs at 133MHz.  Unfortunately, we have yet to see any memory capable of reliably operating at this frequency which makes this more of a “wouldn’t that be cool” than a reality. 

The Virtual Channel SDRAM support of the 133/133A chipsets is an interesting feature, but it is a relatively unused feature due to the lack of availability of VC-SDRAM modules in the market today.  It is unlikely if this will change as VC-SDRAM is nothing more than an intermediate solution to resolve the issues of memory bandwidth limitations until a more bandwidth friendly standard, such as DDR SDRAM, can be adopted and implemented into motherboard designs. 

In addition to the relatively unavailability of VC-SDRAM, our tests have concluded that the performance of VC-SDRAM isn’t all that it’s cracked up to be.  It is barely faster than SDRAM in most situations and in some cases it is actually slower than regular PC100 or PC133 SDRAM, something which is most likely the fault of a flawed VC-SDRAM implementation in VIA’s memory controller. 

Needless to say (it’s something we can’t say enough), VC-SDRAM isn’t something you should lose sleep over.  It’s not something that you’re missing out on, simply because the performance isn’t there.  While the technology behind it is definitely interesting, it’s not worth the trouble at this point in time.