ASUS CT-479 Adapter

So, Pentium M processors use a Quad Pumped Bus analogous to the one employed by Pentium 4 CPUs. What prevents the users from installing the Pentium M on desktop platforms, the marketing restrictions put aside?

First, the Pentium M is inserted into Socket 479 which is pin-compatible neither with LGA775 nor with Socket 478. It seems to be easy to remove this problem by simply adjusting the mainboard’s wiring. But the problem is the input/output buffers of the Pentium M use a different signaling voltage than ordinary chipsets. The I/O buffers of the Pentium 4 use the same voltage as the core, but the Pentium M’s buffers work at a voltage reduced by 1.05V. This is the reason for the Pentium M to be so poorly compatible with classic chipsets.

Anyway, this obstacle proved to be surmountable. Engineers from ASUS developed a special adapter for using Pentium M processors in Socket 478 mainboards based on i875/i865 chipsets.

The ASUS CT-479 adapter solves all the problems concerning the pin assignment differences between Socket 478 and Socket 479 and deals with the electrical compatibility issues. So, if the mainboard’s BIOS supports the Pentium M, you can use Intel’s mobile CPUs in desktop mainboards with the help of this adapter.

There not so many mainboards compatible with the ASUS CT-479, though. There are as yet five of them: ASUS P4P800 SE, ASUS P4P800-VM, ASUS P4C800-E Deluxe, ASUS P4GD1 and ASUS P4GPL-X. These mainboards contain Pentium M-related microcode in their latest BIOS versions which ensures their compatibility (through the ASUS CT-479 adapter) with Pentium M and Celeron M processors based on Dothan and Banias cores. Unfortunately, mainboards from other manufacturers do not work with the ASUS CT-479 because they lack the BIOS support of the Pentium M.

The processor installed via the adapter is powered through the mainboard’s standard voltage regulator – the CPU doesn’t “see” the adapter at all. That’s why the ASUS CT-479 does not support Low Voltage and Ultra Low Voltage processors: the power converter of Socket 478 mainboards cannot output the voltage required for them. Besides that, the users have to sacrifice Enhanced Intel SpeedStep technology if they use the adapter – the Pentium M installed into a Socket 478 mainboard via an ASUS CT-479 does not vary its default frequency.

The installation of the converter into the system is simple and intuitive. After you attach it to the mainboard’s Socket 478, you must select the bus frequency of the Pentium M processor (400 or 533MHz) with the jumpers and attach additional power to the converter. The ASUS CT-479 comes with a special cooler for Pentium M processors. This cooler can be mounted on Socket 478 mainboards using the enclosed fasteners.

There’s nothing exceptional about this cooler: it consists of a rather small aluminum heatsink and an 80mm fan with a maximum rotational speed of 3000rpm. Being originally a notebook-oriented processor, Pentium M doesn’t dissipate too much heat and is quite satisfied with such a simple cooling system.

So, the advantages of the ASUS CT-479 are obvious: this adapter allows using Pentium M processors in ordinary Socket 478 mainboards. It means desktop systems with this processor will be able to benefit from a dual-channel memory controller and a full set of additional controllers available on advanced Socket 478 mainboards from ASUS. But you have to sacrifice Enhanced Intel SpeedStep technology to use the adapter.