In SpetzNaz's post above he was tlaking about XP not vista BTW. Even though his said vista he meant XP.
Once again - I will try to explain ths so everybody knows (,.... crap, if only the stuff i wrote actually got read, or saved....,)
Windows 95, 98, 2000, ME, and XP are all 32bit operating system (although windows XP pro is availible in 64bit). Everything in a computer gets stored as either a zero or a one called a bit.
a 32 bit processor (or 32 bit operating system) is a system which uses commands which are 32 bits in length. For example: there might be an instruction which looks liek this in code "add $5, $4, $3" which will add the values in register 3 and register 4 and then store their sum in register 5. The processor / operating system will see this "00000001000000110000010000000101" which might be the binary equivalent of the code to add registers 3 and 4. (Binary is the name for the number system which uses only zero and one).
In a 32bit system since there are only 32 bit locations then the system can address memory from 00000000000000000000000000000000 all the way up to memory 11111111111111111111111111111111. Incase you are wondering how much memory that is it is exactly 2^32 = 4294967296 (4 GB of memory). When you put in 4 GB of memory into windows XP as Spetz had mentioned it may show up as a smaller value as windows and other system resources will be using the excess.
In a 64 bit system, the processor instructions are 64 bits in length which allows for 2^64 of memory to be used (about 4 Exa-Bytes) Windows Vista will not allow 4 EB of RAM to be installed simply because they probably dont expect that number to exist in the near future. If for any reason it might they would patch it (which they have done in the past for RAM and hard drive sizes). Most motherboards today provide the actuall limit for your copmuter system because they chips they use for their northbridge and any other memory controllers they may use also have made assumptions about the ammount of memory being used. So even though Windows vista might handle 8GB of RAM, my motherboard may only support 4 GB, to find otu I would have to proporly check with my motherboard manufacturor or system administrator. LOLZ just kidding, my computer can handle 8 GB but the point is that yours may not.
Also note that a 64bit processor running a 32bit operating system is effectively running as a 32bit processor and thus can also only support up to 4 GB of memory.
Also further note that 4294967296 Bytes of RAM exactly equals 4 GB of RAM because there is not 1000 bytes in a kilobyte but rather there is 2^10 = 1024 bytes in a kilobyte. 4294967296 / 1024 (for kilobytes) / 1024 (for mega bytes) / 1024 (for GigaBytes) exactly equals 4.
P.S. I know this isnt the best explination but i lost my will to type this info well after the first two times. heh.
