Tell me, if the CPU is tapped at 100%, and there is 4GB installed, & is not using that, how can doubling it to 8GB make things any faster?
No! You cannot relate CPU utilization with the amount of available RAM in that matter. They don't work together in that way.
I say again, the speed and utilization of the CPU have nothing to do with the "amount" of RAM a CPU can work with. You can have 32Gb of RAM with 31Gb free and still have a CPU maxed-out at 100%. Conversely - and typically, you can have just 2Gb of RAM and the CPU sitting at idle between 0 and 1% most of the time, and still have all your security programs running and your email, Word and browser open too.
A slower CPU does NOT imply - in ANY way - that it can only use a lessor amount of RAM. Nor does it in any way imply it cannot benefit from more RAM. That's because Windows makes it happen (within 32 and 64-bit limits of course). But not just Windows. The bus and other motherboard devices restrictions can impact that too.
with my desktop PC, it has a dual core CPU running at 1.5GHz, it seldom runs lower than 70% on Win 7 Pro x64.
Then you got something wrong. CPU utilization should sit at or near 0% for the vast majority of the time, and only peak at such levels occasionally, and for short periods of time. If your CPU is running at percentages above 10 - 20% most of the time, then you need to be scanning furiously for malware, or some benchmarking program, or corrupt service that has gone berserk. Some games may take that percentage up, but even the game should drop it back near 0 when idle.
I suggest you check TM to see what has gone wild (but remember, this is not your thread).
With more RAM the OS does not have to shove such huge chunks of data off to the slow page file. Instead, it can just stuff it in fast RAM. That alone can make a huge difference as a small amount of RAM simply means the CPU and OS will have to utilize the slow page file more. Even the slowest CPU and RAM are many times faster than the fastest hard drives.
But even if my MB could hold 8GB RAM, I cannot see having enough programs open to use it, it would crash first.
What? Crash first? Ummm, no. The
ONLY way more RAM could cause the computer to crash (assuming it is compatible and not faulty) is if the PSU could not handle the extra demand. But if adding RAM stressed out a PSU that much, it was already too small.