What is the reason behind system reading low memory

I need some advice on low ram read. I am building a high end system which is going to have 8GB RAM, 2TB Space and Quad Core Processor. The motherboard will be any latest one. I am having a machine at my office which has 4GB RAM and just to test I added 2 more sticks of 2GB. But the system does not shows full memory. I do not understand this. Atleast in bios the system must tell the complete ram amount even if it is not utilizing it. For server where even 16GB ram is not enough upgrades can be a waste of money.

That basically depend on the hardware architecture. Like a 32bit system which is not capable of reading above 4GB RAM, while a 64bit hardware architecture gives you more. Now this happens on the hardware level. So whenever you are building a pc remember to choose the right amount of hardware and test compatibility. You can find ample of resources on web. The important part is to choose the right motherboard. You can easily checkout in the specification what maximum ram it supports and the type of cpu to add.

Yes that is correct, as 32 bit os won't take complete RAM, as if we insert 4 GB RAM it says 2.50 GB usable. So it was already been discussed and they have informed to upgrade to 64 bit os to gain full RAM access.
P.s. even if it says 2.50 usable it still will provide you the complete 4 GB ram power.

There can be some software level fault also. My system was not reading another 2GB RAM. I was having 4GB in total. I am using Windows. I found a solution on Microsoft site that really worked. On software level the problem can be with himem.sys file. This file is not able to utilize the complete memory available due to which you found low ram. You have to go in bios and check out the necessary settings and ensure that all ram are detected there. On software level it is easy to troubleshoot.