In theory this shouldn’t happen, since there isn’t a limitation in 64 bit Operation System to limit the memory to only 4GB. In fact, depending on what version of Windows 7 you are running, a 64 bit system can support up to 192GB of RAM (Windows 7 Home Premium supports 16 GB Max). But if you are one of those who is experiencing less useable memory than what you suppose to have there might be few reasons why.
Above is a screenshot of my system when I build my new desktop just few weeks ago. It tells me I have 7.49 GB useable out of 8 GB. Why is the case ? Let’s dig deep into resource monitor and see why is the case.
If you go to Task Manager > Performance Tab > Resource Monitor
Go to the memory section, you will see a part of your memory is some how labeled as “Hardware Reserved” 521MB in my case. Why so ?
Well, chances are this means some how your video card is “stealing” your system memory into their “Video Memory”. It depends various on the hardware you have on your system. If you have a dedicated graphic card, this shouldn’t happen, but if you are those geeks that have tweaked your msconfig to set “Maximum memory” in the advanced boot option, during boot time. Your system will maximize and allocate as much as it can to the video memory, even though you might have a dedicated graphic card.
To fix this, just go to msconfig and uncheck “Maximum memory” option in the Advanced boot section, and restart your machine.
Once you restarted your machine, go to your system preference again, and you will see you just got yourself some memory back to your main system.
If this is what you are experiencing hope that solves your mystery “Memory unusable” issue in Windows 7.