Chip magicians at work: patching at 45nm

It is one thing for the chip to be functionally OK, but it also needs to achieve the desired clock speed. As long as the speed isn't satisfactory, the engineers will want to know which 'speed paths', bottlenecks in the circuitry, need to be fixed in order to take things to the next level.

The lab where this is done has been set up in much the same way as the one described in the previous section: a room packed with 19" racks, with every case containing a motherboard specifically designed for testing purposes. These test boards use standard chipsets, but have been augmented with dozens of extra connections around the processor, to enable the engineers to read all sorts of data while the system is running. An ordinary pc sits above the system being tested, issuing experiments and collecting the results.

The main difference between the logics lab and the circuitry lab is that here, the engineers also play around with clock speed and temperature. At Intel, an advanced form of 'temperature control' is used, a central liquid cooling system that allows temperatures to be set in a range between -50 and 80 degrees Celsius.

The goal of the so-called 'circuit marginality validation' is figuring out what the maximum clock speed and temperature is at which the chip can still pass all tests. As soon as the chip starts failing or the level of cooling required is deemed too high, the engineers will try to find the cause of the problem. In most cases, a circuit that performs subpar can be found.

The obvious question whether Penryn has been overclocked in this lab was answered with broad smiles, but no engineers were willing to comment on whether they managed to exceed the 5,56GHz mark which was shown by XtremeSystems. The triple phase change cooling system which was used for that particular effort is definitely more advanced than the gear in the circuit lab, but on the other hand only Intel has access to the guts of the chip.