Overclockers must pay toll to play on Haswell highway

[CyberAbc 290]

Intel has taken back the gift of "free” overclocking that it gave hardware tweakers when introducing its Sandy Bridge and Ivy Bridge processor lines. Geoff Gasior at The Tech Report writes that has Intel confirmed it will lock down the ability on the company's new Haswell generation of CPUs. Users will lose much of the ability to run all but the more-expensive K-series of Haswell CPUs faster than their rated clock frequency in the hope of squeezing more performance out of the processor.

Sandy Bridge and Ivy Bridge processors allowed for overclocking across their whole lines—not by a huge amount, but by enough to squeeze an extra 400 MHz of compute cycle out of them on the “standard” CPUs. Overclocking could achieve even more on the K-series versions.

An Intel representative told Gasior that since the standard Haswell processors are targeted for business and consumer applications “where overclocking is generally not performed,” access to the additional base clock straps of the Haswell processor are disabled in all but the K-series processors. Those run $20 to $30 more than the standard processors. (There is still a “turbo” multiplier mode available to boost performance of the CPU itself, however.)

The K-series CPUs don’t include a number of the features that make Haswell attractive. These include VT-d I/O device virtualization, which allows virtual machines to get better performance out of a  shared I/O device by dedicating it to a specific VM, and TSX extensions for transactional memory, which lets threads of a program to run in parallel and roll back changes if a required thread fails to complete (instead of locking access to the memory down to a specific thread).

The Tech Report’s test crew found that the Haswell K-series processors also had less overhead for major overclocking than their Sandy Bridge and Ivy Bridge predecessors, and the K-series has been found to run much hotter as well. Pushing a Haswell i7-4770K processor to 4.7 GHz required water cooling to keep it stable, while an Ivy Bridge processor tested last year hit 4.9GHz with just air cooling.