Crucial says I can upgrade to 2x DDR3 PC3-12800 while Memory Stock gave me 4GB of PC3-10600. I read from ARK that my chipset are supposed to accept 2x 4GB of RAM though it never mention what speed.
My motherboard model is A42JZ & Laptop Model is A42J Series.
Curse of HM55 Chipset:
The problem is that the HM55 chipset does not recognize modules assembled with inserts RAM 512Mx8bits ... having your limit 256Mx8bits.
So make sure that the memory module that will buy your mount has taken 16 tablets 256Mx8bits, otherwise will not work.