Open resource monitor in windows to see detailed memory usage of programs. There you'll see memory used by programs is divided into working set, shareable and private groups. Now, task manager only shows the private memory used because
it is the "Amount of physical memory in use by the process that cannot be used by other processes". Windows works by actively managing memory by swapping parts of physical memory not immediately needed to hard disk in pagefile. See the performance tab in task manager to see that all the available memory is not free. Some of it is cached. Below it only the paged kernel memory is shown; but even more memory is virtual, i.e. paged to HDD for other processes. For example, of my 4GB RAM, 1.43GB is now being actively used as private, but more is cached, so that free RAM varies between 300-700MB. And more memory is paged. The commit(virtual) memory shown in resource monitor sums up to nearly 1GB. So total physical+virtual memory used now is >4GB. But that doesn't mean my system lags/stutters or windows low memory warning is shown. If I increase my RAM windows will adapt itself to using less virtual memory by writing to pagefile and save HDD life. So windows will always keep some free RAM for immediate use no matter what the amount of RAM installed(of course I am not talking of those 256MB/512 MB era). Some of my friends run Win7 without any problem on 2GB RAM. 64bit Windows may use more RAM than 32bit versions. Whatever, know that if you are not going to use an SSD and turn off pagefile, your 8GB is sufficient to handle what you generally do. Unless you are shown the low memory warning which is extremely unlikely, or your system lags due to excessive pagefile use, know that you can rest assured.