I can't allocate more RAM to Minecraft

I've looked at many different tutorials and Q&A websites, but I can't get it to work.

Right now Minecraft will only start if I have the -Xms1G JVM argument; if I try to increase it, I get the error:

Error occurred during initialization of VM Could not reserve enough space for 2097152KB object heap.

It sounds like either I don't have enough RAM available, or there's a program keeping Minecraft from taking up that much RAM. However, I have 8GB of RAM, so I have way more than enough.

Does anyone have any ideas on what's keeping me from increasing the amount?

If you are going to use JVM arguments to define the memory allocation, be sure that you are not providing duplicate commands.

-Xms1G will set the MINIMUM HEAP to 1GB at start-up.

-Xmx1G will set the MAXIMUM HEAP to 1GB at start-up.

Generally, when I need more memory for Minecraft, I set the max heap and not the min heap.

For example;

java -Xmx2G -jar minecraft.jar

you could also set it like this:

java -Xms1G -Xmx2G -jar minecraft.jar

Avoid allocating too much RAM since that will starve the rest of the machine.

Okay, apparently I was using the 32-bit version of Java. I installed the 64-bit version and everything's working now. Thanks for your answers and comments, everybody!