Windows 7 - acer aspire ram

does my acer aspire as8730-6918 need two ram cards the same size or can i run different cards like a 2gb and a 4gb what limits the maximum capacity would like to install 8gb 4gb x 2 the maximum capacity is 4gb what governs the maximum capacity can i change any parts like the chipset or bois want to run 6gb - 8gb pc6400 backwards compatible

The original hardware governs the max amount of RAM per slot and total allowed. It's very unlikely a BIOS update would add support for more RAM. Putting a 4 gig module in would likely result in only 2 gig being used, if it works at all. It's impractical to try and change the chip-set, it's soldered to the motherboard. Even if you could have it done it would cost you more than the laptop is worth with no guaranty of success. You'll more than likely just brick your laptop.

I HIGHLY recommend running Crucial's memory compatibility scan before you buy anything. I wish I had. I have an Acer Aspire 7750G-9657. I bought Kingston RAM from Newegg that matched all the specs that Acer said a RAM stick needed. I put it in only to discover the system didn't like it one bit. I called Acer Tech Support, and they verified the incompatibility.

Use the Crucial System Scanner software to find out what type of memory is in your computer

When it comes to the Acer Aspire, don't trust anything unless the sticks state that they ARE compatible with the Aspire (and even THEN, they may not be compatible with YOUR model)