Originally posted by: pm
Originally posted by: Foxery
Originally posted by: Lord Banshee
But i do not think the only reason to do is not for overclockers, but so OEM dealers don't sell cheaper processors that work at higher multipliers.
I believe this actually happened a few years back, and is Intel's biggest motivation for locking up its chips.
This was, in my personal experience, the ONLY motivation for locking microprocessor clock ratios. I was directly involved in the first ratio locked CPU's shipped from Intel - I worked on the later steppings of the P54CS product (P54CS was the 133-200MHz Pentium product). After the P54CS release, there was widescale "remarking" of 133MHz parts as 166MHz and 120MHz parts as 150MHz in various parts of the world. Merely by changing the engraving on the top of the chip (by, for example, putting a sticker over it), an unscrupulous vendor could increase their markup by $100-200. Within a year, there were whole organizations that would do this as almost a production line.
The problem was that when the CPU's that had been "remarked" failed, then the customer turned to Intel for a replacement, and were generally unhappy with the quality of this expensive CPU that they had bought, which reflected poorly on Intel.
So, a metal mask change was made which "locked" the ratio to either 120/133 or 150/166 or 200MHz. This was a low-level mask change, there was absolutely no way that anyone could override it - even with a FIB (Focused Ion Beam - a large device the size a refrigerator that can rewire chips) because you'd have to cut through higher level signal wiring (there was no backside FIB back then because the Pentium was direct wirebond attach).
I was in the design review where this decision was approved. I worked on the team and sat next to the engineer who implemented the lock. At no time did anyone mention overclocking, or anything like it. It was all about eliminating the grey market. I know this for a fact, because I was there.
As far as the original concept of the thread - everyone who replied above is correct. There are two ways to change the ratio setting of a Core 2 Duo or similar CPU once the fuses are blown, but neither are practical for an end-user. You could do a backside FIB - which would be prohibitively expensive and FIB'd parts are known for very short operation (like a couple of months) due to the way the backside is prep'd. Alternatively, if you knew the TAP unlock, and you had insiders knowledge of the scan chains that control the ratio, you could theoretically do a TAP scan-chain override through the JTAG port. But these unlock commands are not known by more than a handful of people within Intel (I know this also from personal experience) and doing a scan override is tricky even when you have access to the documentation, and experts who can help - I also know this from personal experience.
The idea that someone could hack a CPU on the surface seems like it wouldn't be that much harder than unlocking a cell phone, but in reality it is vastly harder. Among other things, the firmware on a cell phone is meant to be modified. It's software essentially and it's designed to be changed. In addition, cell phone components are sold across vendors - like the baseband for a cell phone might come from one chip company, while the firmware is from another, and other components from other companies. In order to make this work, specifications need to be written to be communicated between companies, and software needs to be written to enable developers to develop on it - so there are essentially instructions on how to modify the components which exist and SDK's to help people author firmware. None of this is true inside of a CPU, there is an internal specification but it is not shared outside of the compnay, and there's no such thing as an SDK for modifying a CPU - mainly because it's hard if not impossible to do.
So, in reply to the OP, there is no way that is practical to unlock or hack a CPU. It can't be done - if it could, then there would be a multi-million dollar business opportunity for criminal organizations and they would be doing it.
Patrick Mahoney
Intel Corp.
