Socket M is used in all Intel Core products, as well as the Core-derived Dual-Core Xeon codenamed Sossaman. It was also used in the first generation of the mobile version of Intel's Core 2 Duo, specifically, the T5x00 and T7x00 Merom lines (referred to as Napa Refresh), though that line switched to Socket P (Santa Rosa) in 2007. It typically uses the Intel 945PM/945GM chipsets which support up to 667 MHz FSB and the Intel PM965/GM965 which allows 800 MHz FSB support, though the Socket M, PM965/GM965 combination is less common. The "Sossaman" Xeons use the E7520 chipset.
Socket M is pin-compatible with desktop socket mPGA478A but it is not electrically compatible. Socket M is not pin-compatible with the older desktop Socket 478 (mPGA478B) or the newer mobile Socket P (mPGA478MN) by location of one pin; it is also incompatible with most versions of the older mobile Socket 479. Pentium III-M processors designed for the first version of Socket 479 will physically fit into a Socket M, but are electrically incompatible with it. Although conflicting information has been published, no 45 nm Penryn processors have been released for Socket M.