Sorry to throw a spanner in the works but aint Z brush only 32 bit anyway so 4 gig is the max?

True you can go higher but Z wiull only use the 4 gig available.

I've got 16 gig of in my laptop and 8 in my desktop, best way to find out is to go to https://www.crucial.com/ and use their memory scan.

TBH if its a laptop it's probably going to be maxed out at 4 gig unless its already got a 64 bit OS.