AMD Opteron 842 socket: Socket 940

What the Opteron 842 is

The AMD Opteron 842 is a 1.6 GHz single-core server processor from May 2004. It runs one K8 core at 1.6 GHz with no turbo, so 1 core gives 1 thread. Cache is 1 MB of L2 on a 130 nm process. Power is rated at 82 W in a Socket 940 package with part number OSA842CEP5AV in the CG stepping.

The 842 steps the 800 series from the 1.4 GHz 840 with flat cache and power, using a 200 MHz clock with an 8x multiplier at 1.50 V and an 800 MHz HyperTransport link. AMD listed it at 698 dollars in May 2004, matching the 840 CG price while adding 200 MHz. The chip supports MMX, SSE, SSE2, Enhanced 3DNow, NX bit and AMD64 with registered PC3200 DDR. Early B3 revisions topped out at PC2700 with higher launch prices above 1200 dollars.

Multi-socket coherence separates the 842 from 100 and 200 series parts at the same clocks. The 842, the 142 and the 242 all run 1.6 GHz with 1 MB, yet only the 842 enables four- and eight-socket operation. That scope is why the 842 cost more than single- and dual-socket neighbours with identical frequency.

Socket and motherboard compatibility

The Opteron 842 fits Socket 940 multi-processor boards with registered DDR and SledgeHammer 800 series support. It needs a four- or eight-socket board, not a one- or two-socket board. The Socket vs chipset: what decides whether a CPU works guide covers pairing rules.

Multi-socket database servers are the natural match. Boards listing 800 series parts accept the 842 with matched 82 W cooling per socket. Single-socket 142 and dual-socket 242 parts do not enable extra sockets, even though clocks match.

Memory, PCIe and cooling

Memory is registered DDR with ECC per socket, reaching PC3200 on CG parts. Balanced populations across all sockets give full coherent bandwidth. Desktop modules do not boot.

HyperTransport at 800 MHz meshes all CPUs and the chipset, while expansion hangs off the chipset. No PCIe lanes originate on the die. Cooling uses 82 W qualified heatsinks per socket with strong chassis airflow. All sockets need equal service for stable operation. DDR2 needs later sockets.

Upgrade paths

On Socket 940 the steps are the Opteron 844 at 1.8 GHz and the 846 at 2.0 GHz for multi-socket boards. Athens 842 successors on 90 nm add SSE3 where listed. Beyond Socket 940 a move to Socket G34 needs new boards. The 842 lifts with the lever, so swaps need no solder work.