I have a Compaq1500N notebook with a Pentium 4 desktop cpu in socket 478 and fsb of 400MHZ. It runs very hot and I am very tired of hearing the fan after 3 years. What are my upgrade possibilities for the CPU? Mobile Pentium 4 up to 2.4 ghz seems possible. What about a Pentium M 735 with a FSB of 400 MHZ made for socket 478. It runs cooler, uses the same socket, and has the same FSB. Are there other critical issues for compatibility in a notebook? With the 735 I'd keep it for a year more.