Bypassing Intel's Overclock Limit Reveals DDR2-667

BatonRogue writes "Slashdot posted a Tomshardware article talking about Intel's 10% overclock limit on their new chipsets not too long ago. The situation has just become even more interesting. AnandTech just posted a roundup of DDR2 memory that sheds some light as to why Intel may have implemented the lock. It seems that on the Abit board they tested, which supposedly bypasses the overclock limit, the first generation of DDR2-533 memory modules had no problems working at 667MHz. Could it be that Intel is keeping DDR2-667 support for yet another revision of their new chipsets even though the memory support is clearly here today?"

Comments

Re:Well...

[Jennifer E. Elaan]

It used to matter a lot more back when you could really overclock a processor. My old dual-celeron used to run decently at 550MHz, when it was originally specced at 366. I think ion migration finally started to set in, though, it doesn't take the higher speed properly anymore. Otherwise, it's still running (at 366) to this day.

I'm one of the original overclockers. I had a 486DX36, back when overclocking required replacing the clock module on the motherboard. I'm also an occasional chip designer.

The trick to overclocking is to know what your limit is. Until recently, thermal load was not the limiting factor. The real limiting factor was a condition called "metastability", where a digital transition fails to finish before being latched in the next register (usually due to violations of the setup and hold time restrictions of those registers). The smallest case of metastability can flip a bit.

A larger case can cascade through multiple stages, flipping lots of bits or even pushing the state tables into illegal states. This is where the first real danger lies: a processor that uses one-hot encoding to improve the speed of the controlling state machine can be pushed into illegal states that may cause several circuits to drive the internal busses at once. This leads to large current dissipation, and in some cases it can burn holes in the thin metal layers of the IC.

A less common hazard appears in cases when the CPU is massively overclocked. The CPU in such a case will never exit the metastable state. This causes each clocked circuit on large areas of the chip to dissipate maximum current during those metastable states. This can also lead to high current dissipation, although it is less dangerous than the abovementioned one. It's also worth mentioning that a chip in this state will not function normally.

Generally speaking, you have a wide margin between the onset of metastability and the onset of serious damage. Unfortunately, there is now *another* danger of overclocking processors. High thermal load can cause ion migration. In fact, most processors are now designed to only last 5 years (!) before ion migration renders them useless. (This is also why I personally don't overclock anymore).

It's frightening to notice that mainstream CPU's are less and less overclockable and have higher and higher thermal loads with smaller and smaller featuresizes, though. The manufacturers are simply not leaving as much margin as they once did.