Review: AMD Athlon 64 X2 4200+ to 6400+ Upgrade
The AMD Athlon 64 X2 6400+, the fastest processor among dual core Athlons, is clocked at 3.2GHz. This Socket AM2 64-bit CPU has a total of 2MB of L2 cache and a 125W thermal design power. It is produced using older 90-nanometer technology, although AMD also makes some less power-hungry and cooler 65nm Athlon 64 X2 chips.
This particular product – model ADX6400CZBOX – comes with heatsink and fan. AMD also offers the Athlon 64 X2 6400+ Black Edition ADX6400CZWOF with an unlocked multiplier. It ships without a cooling device.
AMD Athlon 64 X2 4200+ vs 6400+ Benchmarks
I have replaced an old Athlon 64 X2 4200+ at 2.2GHz with the 6400+ in a Windows Vista desktop PC machine featuring the Asus M2N-E SLI motherboard, 2GB of 800MHz DDR2 memory, the Asus EAH3850 512MB video card, and a Cooler Master 620W power supply. The performance improvement after this upgrade is significant and goes up to 46 percent in some tests.
| CPU | AMD Athlon 64 X2 6400+ | AMD Athlon 64 X2 4200+ |
| Frequency | 3.2GHz | 2.2GHz |
| L2 Cache Size (KB) | 2X1024 | 2X512 |
| Socket | AM2 | AM2 |
| Stepping | F3 | F2 |
| Manufacturing Tech (CMOS) | 90nm SOI | 90nm SOI |
| Wattage | 125 W | 89 W |
| System Bus (MHz) | 2000 | 2000 |

The upgrade from the 4200+ to 6400+ increases Windows Experience Index in Vista OS from 5 points to 5.5 points, in both overall and CPU calculation tests.

In the default PCMark 05 test the 6400+ is 30% faster than the 4200+.

In PCMark 05’s CPU-specific benchmark the difference is even greater. The 6400+ CPU is approximately 46% faster.
The default 3DMark 06 benchmark shows the 6400+ is 18 percent faster.

In 3DMark 05 CPU-related test the Athlon 64 X2 6400+ CPU has an advantage of 43% over the 4200+.

Obviously, the 6400+ outperforms the 4200+ in Cinebench 10, which is based on Cinema 4D software for 3D content creation.
Crysis, a hardware-demanding first person shooter game, shows greater performance advantage of the 6400+ CPU, especially when playing in lower resolutions.

World in Conflict real time strategy game runs a lot smoother with the AMD’s top of the line Athlon CPU.
However, the Athlon 64 X2 6400+ has some disadvantages when compared to the 4200+. These are greater power consumption and higher temperatures during work. The 125W 6400+ and 89W 4200+ processors with their stock coolers generate 35C and 25C temperature on idle respectively. Under heavy load (PCMark 05 CPU test) these temperatures are 48C and 35C.
Conclusion: AMD Athlon 64 X2 6400+ – a Good AM2 CPU Upgrade
Currently priced at around $160, the Athlon 64 X2 6400+ is certainly much pricier than the $70 4200+ processor. However, it is an affordable price for a 3.2GHz CPU and it is worth it, if you consider its huge performance advantage over the slower and cheaper 4200+ chip. On the other side, the 4200+ runs cooler than the 6400+. If you use your desktop PC only for light work (such as web surfing or word processing) the slower CPU will suit your computing needs with less generated heat and lower power consumption. But, for hardware demeaning users, i.e. gamers and video editors, the 6400+ is a good choice. This does not apply to overclockers. They should rather buy the Athlon 64 X2 6400+ Black Edition and pair it with some of the more powerful after-market CPU coolers. Considering its price/performance ratio, I can recommend for sure the 6400+ as a Socket AM2 upgrade option or for a fresh AMD-based PC build.
AMD Athlon 64 X2 6400+ 3.2GHz Socket AM2 125W Processor
AMD Athlon 64 X2 6400+ Black Edition 3.2GHz Socket AM2 125W Processor

I have an Athlon64 X2 6400+ Black Edition, and I can 100% tell you that it does NOT have an unlocked multiplier.
It allows you to reduce the multiplier – but not increase it.
16x is the highest it allows (16x 200Mhz = 3.2GHz).
The Athlon64 X2 5000+ Black Edition however, DOES have an unlocked multiplier – but it cannot overclock to the same speeds the 6400+ can, so it’s not worth it.
I manage to run my 6400+ at 3.66GHz/Core (229MHz FSB) with 100% stability using a Scythe Mine cooler and AS5 Thermal Paste. The highest temp I’ve seen from it under load with a 48°C case temp is 61°C.