VIA C3 Processor 866A socket: Socket 370

What the C3 Processor 866A is

The VIA C3 Processor 866A is an 866 MHz single-core desktop processor from September 2001. It runs one Centaur Ezra core at 866 MHz with no turbo, so 1 core gives 1 thread. Cache is 64 KB of L2 with 128 KB of L1 on a 130 nm process. Power is rated near 9 W in a Socket 370 ceramic PGA package on a 133 MHz front side bus with a 6.5x multiplier at 1.35 V.

The A suffix mirrors dealer strings also seen on 900A parts, which is why the 866A at 866 MHz matches the plain C3 866 at the same clocks. VIA sold the 866A in September 2001 with the plain 866. The chip supports MMX, 3DNow and LongHaul.

An 866 MHz clock on a 133 MHz bus suits Socket 370 value boards with PC133 memory and small coolers. The 6.5x half-ratio needs an exact BIOS string. That is why the 866A shipped in budget office towers.

Socket and motherboard compatibility

The 866A fits Socket 370 value desktops with Ezra support. It needs a 370-pin board with a 133 MHz bus path and a BIOS that lists VIA C3 Ezra parts. The Socket vs chipset: what decides whether a CPU works guide covers pairing rules.

Value PC133 towers are the natural match. Boards listing C3 Processor 866A accept the chip with a 9 W cooler.

Memory, PCIe and cooling

Memory is PC133 SDRAM through the board chipset at the 133 MHz bus rate, matched to the board DIMM sockets. The CPU has no memory controller. Value Apollo boards commonly run PC133 pairs.

A 133 MHz front side bus ties the CPU to the chipset, while AGP and PCI hang off the chipset. No PCIe lanes originate on the die. Cooling uses the Socket 370 lug clip with a cooler rated for 9 W.

Upgrade paths

On the same socket, a move to a C3 Processor 900A such as VIA C3 Processor 900A adds 34 MHz on a 100 MHz bus when the board carries both bus tables. A C3 Processor 866T such as VIA C3 Processor 866T is the Ezra-T counterpart at the same clocks with copper interconnects.

A move to Nehemiah adds SSE support. The Socket 370 page lists the range for planning.