AMD Opteron 846 socket: Socket 940

What the Opteron 846 is

The AMD Opteron 846 is a 2 GHz single-core server processor from December 2004. It runs one K8 core at 2 GHz with no turbo, so 1 core gives 1 thread. Cache is 1 MB of L2 on a 90 nm process. Power is rated at 85 W in a Socket 940 package with part number OSA846FAA5BM in the E4 stepping.

Athens moves the 800 series from 130 nm SledgeHammer to 90 nm with SSE3 instructions and a 1000 MHz HyperTransport link. The 846 at 2 GHz with 1 MB shares clocks with the SledgeHammer 846 at 89 W, yet the Athens bin trims power to 85 W while adding the newer instruction set. AMD listed the Athens 846 at 698 dollars in December 2004. The chip supports MMX, SSE, SSE2, SSE3, Enhanced 3DNow, NX bit and AMD64 with registered PC3200 DDR. A duplicate cpu_list row repeats the same Athens 846 spec, so one page covers both entries.

Multi-socket scale with a die shrink defines the appeal. Eight Athens 846 parts give eight cores at 16 GHz aggregate with 8 MB total L2 at 680 W of CPU power, against higher power for SledgeHammer equivalents. That efficiency with SSE3 suited large shared-memory systems that needed socket count and modern instructions together.

Socket and motherboard compatibility

The Opteron 846 Athens fits Socket 940 multi-processor boards with registered DDR and Athens 800 series BIOS support. It needs a four- or eight-socket board qualified for 90 nm Athens parts. The Socket vs chipset: what decides whether a CPU works guide covers pairing rules.

Large coherent servers are the natural match. Boards listing Athens parts set voltage to 1.35 V to 1.40 V with SSE3 paths and 1000 MHz HyperTransport operation. SledgeHammer-only boards may seat the chip yet miss Athens microcode. Single-socket 146 and dual-socket 246 parts do not scale to eight sockets.

Memory, PCIe and cooling

Memory is registered DDR with ECC per socket, reaching PC3200. Balanced DIMM populations across all sockets give full coherent bandwidth. Server modules only.

HyperTransport at 1000 MHz meshes sockets and the chipset, while expansion hangs off the chipset. No PCIe lanes originate on the die. Cooling uses matched 85 W heatsinks per socket with strong chassis airflow. All sockets need equal service for stable coherent operation. DDR2 needs later sockets.

Upgrade paths

On Socket 940 the steps are the Opteron 848 at 2.2 GHz and the 850 at 2.4 GHz in Athens revisions for multi-socket boards. SledgeHammer 846 at 89 W is the 130 nm alternative without SSE3. Beyond Socket 940 a move to Socket G34 needs new boards. The 846 lifts with the lever, so swaps need no solder work.