AMD Phenom II X4 840 socket: Socket AM3

What the Phenom II X4 840 is

AMD Phenom II X4 840 is a quad core Propus processor that AMD released in January 2011 for mainstream desktops. It uses the K10 core design on a 45 nm process, running at 3.2 GHz with no turbo. The cache is 2 MB of L2 with 512 KB per core and no L3, which marks it as an Athlon II X4 die sold under the Phenom name. Power is 95 W. The retail box carries part number HDX840WFK42GM on a Propus C3 stepping. The HyperTransport link runs at 2.0 GHz, and the 938-pin package fits the 941-hole AM3 socket as well as 942-contact AM3+ sockets.

Four cores at high fixed clocks cover office multitasking and light threaded work without turbo steps. The chip keeps the dual channel DDR2 and DDR3 controller, so both memory generations work. No integrated graphics exist on the CPU, so boards use chipset video or a separate card.

Towers pair it with 880G or 890GX boards, 4 GB of DDR3 and chipset video or a basic card. The fixed 3.2 GHz rate with four threads covers office multitasking and light threaded work without tuning. Fixed 3.2 GHz clocks keep single thread response direct. The LGA, PGA and BGA: CPU package types explained guide places this PGA desktop part against BGA mobile forms.

Socket and motherboard compatibility

The Phenom II X4 840 drops into Socket AM3 on 7 and 8 series boards with Propus support. AM3 processors also fit AM3+ boards. Check the maker CPU list for the exact board BIOS, since early 7 series boards need current firmware for C3 steppings.

Power at 95 W needs a standard tower board with a full size cooler. Common homes include 770, 785G, 880G and 890GX boards. Four 4 GB UDIMMs give the practical 16 GB ceiling on most AM3 boards, with ECC only where the board wires it. The Socket vs chipset: what decides whether a CPU works guide covers AMD pairing rules.

Memory, PCIe and cooling

Memory support is DDR2-1066 and DDR3-1333 over two channels. Two matched modules give the rated bandwidth for four cores. ECC works only where the board wires it. Boards with four DIMM slots reach 16 GB with matched kits.

PCI Express slots come from the 7 and 8 series chipset for graphics and expansion. Chipset video covers office monitors, while a mainstream card of the era pairs without waste.

Cooling follows the 95 W rating with a larger stock heatsink on the 48 × 96 mm mount.

Upgrade paths

On Socket AM3 the Phenom II X4 840 can move to Phenom II parts with 6 MB of L3 on the same board, which helps games and threaded work that reuse data. Memory and storage carry over, while the cooler often carries over within 95 W. DDR3 DIMMs move to an AM3+ board as well for a later FX step. A Deneb comparison with L3 is the Phenom II X4 975 BE class on the same socket.

A platform move to AM3+ keeps DDR3 while adding FX parts. Six core FX chips add two threads on the same DDR3 DIMMs for heavier multitasking. Keep the AM3 tower for office duty.