Why do i have a limit on the amount of ram for minecraft?

Ok, so i got some mods for minecraft, but i need to use a lot more ram so they can play without dropping bellow 25fps. They are nuke mods, btw. But anyway, i go into the edit profile in the minecraft launcher, and i try to change my ram limit, but for some reason, i can't go above 1250Mbs. I find this EXTREMELY odd because i have 8gigs of ram. Also, my friend has the same mods and he allocates 7 gigs of ram and he too has 8 gigs. I know its a lot, But i just want to know why my friends can have over 5 times the amount of ram for minecraft.

Do you have a 32-bit or 64-bit operating system (OS)? If it is 32-bit, you wasted your money on 8 GB of RAM because 32-bit can only address about 3 GB, including the operating system, shared video RAM, and any other programs running. If your computer came with 4 GB or more RAM it should have come with a 64-bit OS. If not, you got ripped off by whoever sold you the computer.

I doubt if you need more than 2 GB for minecraft with mods. That is what I use for Tekkit which is minecraft with a bunch of mods. What matters for fps is your CPU and graphics. And regardless of CPU, if all you have is integrated Intel graphics, that may be as good as it gets no matter how much RAM you use.