I am curently using a Toshiba Satellite A300D 11S with a AMD Athlon TK 57 1900 Mhz CPU.
Please tell me what processors are compatible with this laptop's motherboard, and what would be the best upgrade option? (performance and heat management wise).
The CPU supports depends on the chipset and in most cases from BIOS support.
As far as I know the notebook A300D-11S supports the AMD M690G chipset (code name RS690M + SB600)… so you can use only AMD CPUs.
As far as I know the Mobile Athlon XP-M, Mobile Athlon 64, Turion 64 and Mobile Sempron CPUs would be compatible with this chipset… but there is always a open question regarding the BIOS support.