The maximum amount of memory that an OS will recognize varies by type and version of the operating system.
However, if you haven't maxed out your physical memory, all of it will be available for use. If you've maxed out the amount of physically installed memory in your system, the amount of memory necessary to run devices will be deducted from your system's available memory, meaning that you won't be able to use all of your physical memory. Upon startup, your system calculates the amount of memory needed to run devices. The reason? A portion of your system's memory (regardless of how much you have installed) is reserved to run devices, such as any graphics cards, PCI cards, integrated network connections, etc., meaning that certain amounts of installed memory may be unavailable for use as available memory. While the Windows OS allows for a maximum 4GB of installed physical memory, this does not equate to 4GB of availablememory.
The problem revolves around how much memory the OS can address.
The memory you purchased and installed is fine. For instance, when you install 4GB of memory in a 32-bit Microsoft ® Windows ® OS, your system may report only 3GB or 3.5GB of available memory. Not only is there a maximum amount of memory that your system's motherboard can accept, there is also a maximum amount of memory that your operating system (OS) can accept.
