AMD Athlon X4 840 socket: Socket FM2+

What the Athlon X4 840 is

The Athlon X4 840 is a headless Kaveri quad on Socket FM2+ for efficient desktops with discrete cards. It runs 4 Steamroller cores and 4 threads at 3.1 GHz base with turbo to 3.8 GHz. Four megabytes of L2 cache cover multitasking. Power is 65 W on 28 nm from August 2014. No integrated graphics exist.

Lower base clocks than the 860K trim heat while turbo preserves bursts. Four threads handle office work with background tasks. The 65 W envelope fits slim towers with stock cooling. The locked multiplier keeps behavior steady.

DDR3-2133 over two channels feeds four cores. A discrete card is required for displays. Buyers pick the 840 where headless Kaveri threads must fit 65 W.

Socket and motherboard compatibility

The 840 fits Socket FM2+ on A68H, A78 and A88X boards. The 65 W rating suits all FM2+ VRMs. DDR3-2133 DIMMs match stock turbo. A basic discrete card covers setup and office displays.

Dual channel DDR3 serves the cores. The Socket vs chipset: what decides whether a CPU works guide covers AMD pairing. FM2 boards never accept Kaveri.

Memory, PCIe and cooling

DDR3-2133 over two channels suits efficient desktops with SSDs. Fast memory helps CPU bound tasks. DDR3-1866 works where modules exist.

PCIe 3.0 with 16 lanes from the APU feeds one mainstream card. A low profile card suits slim towers. Chipset lanes handle storage.

Cooling uses FM2+ stock coolers for 65 W. Quiet curves suit offices. The locked multiplier keeps thermals steady.

Upgrade paths

On the same socket, the AMD Athlon X2 450 at dual core below saves cost, while the AMD Athlon X4 860K at 3.7 GHz unlocked above adds tuning headroom. All share FM2+ boards.

Newer Athlon quads cover faster duty. The 840 holds efficient headless Kaveri value.