Calculating power consumption of PC...

I am not to write about save power to salvage the drowning world....

Recently I found out that on AMD Dual Core machine, "Smart sharpening" of Adobe Photoshop takes just 2sec to sharpen a image of resolution, 3000x4500. That shook me because same operation takes 40 sec on my 1.8ghz single core PC !!!!
So I started thinking of buying a new motherboard, RAM, Dual Core CPU...
but I wanted to retain existing power supply and was not sure whether it can feed 5HDs and also new Dual Core CPU. So, I wanted to know, how to measure the power consumed by 5 hard disks that are currently sitting in my PC.
This hightly informative and also practical post guided me while estimating the power consumed by devices of my PC.
In the early stages of this research I found out that once started that my 410W PSU can supply the WATS required by 5HDs and DualCore CPU, but in this investigation I found out that what also matters is the power required at the time booting because devices draw their peak current ONLY at the time of booting. So I dug out manufacturer's specification for all HDs and noted down the maximum current needed at the time of booting.
This is my power supply (PSU) specification

As the image shows my PSU could deliver a maximum of 20Amps @ 12V.
Following shows the current drawn by various devices, at the time of booting..

Case fans(3)------->0.5
AMD Dual CPU------->8.24
Total 19.14A

Conclusion: 19.2A is not far from 20A, which is the maximum current that my existing PSU can deliver, so I decided to buy an external harddrive enclosure to host Samsung 250gb SATA drive and this would bring down boottime current demand from 19.2 to 17.1...