It is for voltages mainly yes. Overdrive is limited by hardware.
Read this copyed & pasted from RBE:
Urgent information on overdrive increase
What is this all about? Maybe you tried overclocking your card using overdrive and found yourself running into the upper limit there. ATI implements this limit into their cards to assure the video card vendors don't overclock their chips too much. They just want to have an overview over the market and maybe, want to participate in the more expensive OC edition cards. Thus, the video card vendors make a video card, create a BIOS for it and send this BIOS to ATI. ATI approves the BIOS (or not), adds a signature to it and sends it back to the vendor. Only then the vendor can produce and ship the card, this is not possible without that signature. The signature mentioned is an encrypted key. The overdrive limit in the BIOS is protected by this key. It can be changed, but if so, the key won't match any more which makes the catalyst driver not recognize the card any more and therefore, this BIOS is unusable. RBE can't decrypt this key, but it can transplant an overdrive limit and its key to another BIOS.
Even though this is an attractive method, it has some disadvantages:
1) There must be BIOSes with increased limits and matching signatures. So far, RBE's author is not familiar with so many such BIOSes.
2) The area that needs to be put into the BIOS contains the deviceID, also. If you are keen enough to put a HD 4850 hash into a 3870 BIOS for example (not recommended, though), be prepared for strange things to happen: Programs that make decisions out of a card's deviceID (just like RBE for example) will be fooled then, of course. Maybe you will have to install the matching catalyst for the new card (in this case, the one for the 4850) after flashing and rebooting. But of course, the 3870 is still a 3870, not supporting many things the 4850-catalyst expects to work. Please try not to mix up video card types, at least not among the video card generations (like 3xx0 and 4xx0 for example). The key matching your card best will be suggested by RBE automatically.
I know when i tryed increasing overdrive it messed the gpu up. Gpu not seen by driver.
