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Phenom II X4 840 CPU Review



The new Phenom II X4 840 (3.2 GHz), is a very affordable quad-core CPU. In fact, it is the best CPU on the USD 100 price range. Let’s see why.

At USD 100, the main competitor to the Phenom II X4 840 (3.2 GHz) is the Pentium E6800 (3.33 GHz), a dual-core CPU using the socket LGA775. The cheapest Core i3, the 530, is quoted at USD 120, thus being 20% more expensive than the Phenom II X4 840 and not being its direct competitor. We are going to compare the new Phenom II X4 840 (3.2 GHz) to the Athlon II X4 635 (2.9 GHz), since both are in the same price range.

In the tables below you can see a brief comparison between the CPUs we included in our review. AMD CPUs do not support SSE4 instructions (they have a proprietary instruction set called SSE4a, which is not the same thing as SSE4).

CPU Cores Internal Clock Base Clock Core Technology TDP Socket Price
Phenom II X4 840 4 3.2 GHz 200 MHz Propus 45 nm 95 W AM3 USD 100
Athlon II X4 635 4 2.9 GHz 200 MHz Propus 45 nm 95 W AM3 USD 98
Pentium E6800 2 3.33 GHz 266 MHz Wolfdale 45 nm 65 W 775 USD 100

TDP stands for Thermal Design Power which advises the user of the maximum amount of heat the CPU can dissipate. The CPU cooler must be capable of dissipating at least this amount of heat.

CPU L1 Cache L2 Cache L3 Cache Memory Support Memory Channels
Phenom II X4 840 64 KB + 64 KB per core 512 KB per core None Up to DDR3-1333 Two
Athlon II X4 635 64 KB + 64 KB per core 512 KB per core None Up to DDR3-1333 Two
Pentium E6800 32 KB + 32 KB per core 2 MB total None * *

(*) The memory controller is not integrated in the CPU and thus these parameters depend on the chipset/motherboard. In our case, the motherboard we used supported only DDR2 memory up to DDR2-800 (officially), under dual-channel architecture.

AMD CPUs talk to the external world (i.e. the chipset) thru a bus called HyperTransport. For a detailed explanation how this bus works, please read our The HyperTransport Bus Used by AMD Processors tutorial. The Pentium E6800 talks to the external world through a front-side bus (FSB) running at 266 MHz (1,066 MHz QDR).

In our tests, we used motherboards with integrated video. We used a motherboard based on the AMD 880G chipset with the AMD processors, and a motherboard based on the Intel G45 chipset with the Intel processors. We wanted to keep both systems around the same price range, and this is why we didn’t use a motherboard with a “stronger” chipset (e.g., AMD 890GX) with the AMD CPUs. In our gaming tests, we measured the performance of the integrated video and also installed an entry-level DirectX 11 video card (GeForce GT 430), so you will be able to compare the performance of the CPUs when a “real” video card is installed.