My PC came back from repair and I noticed they'd replaced the 2.1ghz AMD Athlon (clock speed showed 160) with a 1.8ghz AMD Sempron (clock spped shows 200). They replaced the mboad as well. By doing this have they downgraded my PC (smaller processor) or is it actually better (clock speed).

"replaced the 2.1ghz AMD Athlon (clock speed showed 160) with a 1.8ghz AMD Sempron (clock spped shows 200)" You need to clarify which CPUs you're talking about. I'm guessing that they're socket A? And what do you mean by 160 & 200...is that the FSB setting? The clock speed(s) are 2.1GHz & 1.8GHz. Obviously the CPU was downgraded. Try running CPU-Z to identify your CPU, socket type & clock settings: http://www.cpuid.com/cpuz.php

The 160Mhz and 200Mhz refer to the Bus Speeds. So am I right to complain at being downgraded, even if the bus speed is higher ?

I still don't know what CPUs you're talking about! Obviously you don't either. That's why it's important that you run CPU-Z & post back with the results. I'm guessing the Athlon is a socket A Athlon XP 3000+ Barton. However, there are two different versions. One runs at 2.1GHz with the FSB at 200MHz, the other runs at 2.167GHz with the FSB at 166MHz. There are no CPUs that run at 160MHz FSB....at least not by default. And there are no socket A Semprons that run at 1.8GHz, however, the Sempron 2600+ Tbred runs at 1.833GHz with the FSB at 166MHz. There are no socket A Semprons that run at 200MHz...they're all designed to run at 166MHz. Like I said, you have to clarify what you're asking about. I'm just guessing what you have....

Yes your CPU has been downgraded, you should complain to where ever it is you got your computer repaired as they should have given you parts of an equal spec if they are replacing any parts.

This is what CPU-Z says: AMD Sempron 3000+ Code name: Palermo Brand id:38 Package: Socket 754 Core Speed: 1799.6MHz Bus Speed: 200.0Mhz I don't have the old processor but have an old screen dump from Belarc advisor showing it was a 2.1Ghz AMD Athlon XP. Under the main circuit board it shows Bus clock 166 Mhz. Maybe I shouldn't be looking at the bus clock and just the CPU size ?

OK, that helps immensely. Your system WAS upgraded (sort of). You went from a socket A to a S754. However, the Sempron 3000+ wasn't the greatest CPU choice because it only has 128k L2 cache. Your Athlon XP had 512k L2. Even so, due to the differences in technology, your new system *should* be an improvement. Plus you could always upgrade the CPU to an Athlon64. The A64 3000+ or 3200+ is selling for about $30 these days. What's the make/model of your motherboard? The Palermo is a decent overclocker. You should have no problem cranking it up to 2.25GHz (9 x 250MHz).