Rev. A, What does that mean?

Question

I have limited access to the web at this time, and would like a definition of what the "rev" A and B mean. My iMac is at the reseller's for a logic board and, also, for a power supply.
I have read that this can be a continuing problem for the "Rev. A" iMac. Can anyone tell me why? I hate to think that my iMac will die again, just as I start to enter my home movies,etc. I do back up every so often to a LaCie external drive, but if I really push my iMac with movies and such, will this happen again?
Thank you for your attention. I'm not the most tech-savvy person, but I'm trying to learn.  
iMac G5 17", 1.8Gh, 160 HD, ae, bt,1gb ram,iLife 06   Mac OS X (10.4.5)  

Answer 1

The video and power supply problems that some first gen iMacs show are part of a larger "capacitor plague" in the computer industry. It is nothing Apple - or iMac - specific. Bad caps were found in all brands of computers and motherboards. Once Apple replaces the midplane and power supply, you should have no return of the problem.
It has nothing to do with "pushing" your iMac too hard.
Mine were replaced back in August '05 and all is well.
We casually refer to "Rev A" and "Rev B", but there are no such official designations. In a nutshell, the models are as such -
Rev A (or first gen) iMacs had a 1.6 or 1.8GHz G5 processor, 256MB RAM and the 646MB nVidia 5200 video card
Rev B (or second gen or ALS) had a 1.8 or 2.0GHz G5 with 512MB RAM and the 128MB ATI 9600 video card. They also had a light sensor on the bottom that was used to regulate the brightness of the sleep light (called the Ambient Light Sensor - ALS)
iSight iMac is obvious due to the built-in iSight webcam
All come with either a 17" or 20" display.
Lots of info at EveryMac.com that can help you ID almost any model Mac back to the original 1984 model.