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LGA775 Processor Socket

I would like to particularly dwell on the new LGA775 processor socket or the so-called Socket T. The major difference between the new LGA775 and the previous socket is a considerably bigger number of pins (the new socket has 775 pins while the old one had only 478) as well as a completely new socket design. LGA775 processors will have no common pins. Instead there are flat contact spots, which do not stand out from the bottom of the CPU. The spring contact pins are located in the processor socket. The CPU is installed and fixed in this socket by a special framing and a clip lock pressing and holding the CPU real tight for better contact between the contact spots and socket pins.


LGA775 processor socket.

CPU contact spots.

Socket pins (closeup).

However, it is much more interesting to find out what pushed Intel to switch to the new LGA775 Socket form-factor. Of course, the change made to the retention mechanism is a matter of taste. For instance, Athlon 64 FX and Opteron processors use the regular Socket 940 with 940 pins and do not suffer from any mechanical problems. So the use of the new retention mechanism is probably just Intel’s desire to make it even easier and more comfortable for the users to open and close the clip with the new larger cooling solutions used for the new and upcoming Pentium 4 processors with higher heat dissipation and the upcoming transition to the new BTX case form factor.

As for the significant increase in the number of contact pins and spots (to be more exact the number of pins by the new LGA775 got 62% bigger compared with the Socket 478) within the same processor family and same NetBurst CPU architecture, there are multiple opinions available. However, the most likely explanation is Intel’s desire to spread the electrical workload more evenly due to the possibility to duplicate certain important lines, such as power supply lines, in the first place. In other words, in each particular spot of the processor die we observe the reduction of power losses occurring on the transition from the contact spot to the transistor hidden deep inside the die. The more pins are involved under the same overall workload, the lower gets the specific load onto each particular part of the die next to the corresponding pin. As a result, the inductance and resistance in each transitional spot are lower, and the voltage deviations caused by constant switching of the status of tens of millions transistors get smoother. As a result, transistors can work at a lower nominal voltage. And lower voltage certainly implies lower power consumption.

This way, the bigger number of contact pins should help solve two major problems. First, we save some power, which we have already mentioned as one of the advantages of the new LGA775. Of course, the heat dissipation will also get lower in this case. But do not get too much excited yet: we do not save enough to reduce the heat dissipation of the current Prescott based processors. However, in the future when Prescott II based Pentium 4 processors working at 4.0+GHz will dissipate about 150W of heat, any power saving like that would be valuable. Secondly, more pins ensure higher stability of the CPUs at higher clock frequencies. Therefore, the shift to LGA775 may be regarded as a certain preparation for the Pentium 4 processors to move to a faster system bus. LGA775 CPUs are expected to support 1066MHz bus ensuring up to 8.5GB/sec bandwidth.

As for the life cycle of the new LGA775 socket, it will evidently be not any shorter than that of the Socket 478. Intel is going to release Pentium 4 processors on Prescott core at least for next couple of years. LGA775 is expected to be widely used up to 2006. And only in a little bit over two years, when 65nm Nahalem, Merom and Conroe based CPUs should come out, the desktop systems will acquire new processor socket currently known as Socket C.

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