I have spent most of my computing industry experience in the hardware arena. While there has been multiple different configurations and reasons for the hardware, the times have changed almost every year. Going from IDE drives to SATA and the whole SSD vs. RAID drive discussion. While the speed of RAID is usually meant for server technology, its use in the gaming and high-end computer industry is starting to gain a lot of ground.
While recently building a new 3.6Ghz computer, it was good to see all the new tech out there like coolant systems and LED lighting products. My son has been into computer gaming for a long time and he tests my computer skills about once a year with a needed upgrade. We have installed more memory, added a coolant system and two different video cards. He likes going to benchmark websites to flaunt his frame rates. The unfortunate part of this is it usually leads to the next upgrade.
If you already have a system set up thats pretty nice, try visiting a benchmark website to test your computer's ability before investing in a non-useful upgrade. These will narrow down what computer component is best to upgrade for the best kick in performance. I'll suggest that you back up your system consistently and reinstall the Operating System first if you experience lagging. A fresh OS installation is good to do every couple years anyway. This process has become less of a technical fix and well documented by Microsoft and others.
If you are looking at building one, do your research first. What do you want to use it for? Games, office file server, internet browsing, etc. Research what others have recently done to get what you are looking into. You will see key words and phrases that will lead you to the tech you should be investing into. Are you seeing RAID or SSD, a harddrive size or a specific video card that works best? Write these down and research prices for these items. Next, visit a hardware site like ascendtech.us for their sweet hardware configuration page. It is possible to order the case, power supply and some internals, while ordering that massive video card from another vendor. You should be on the lookout for hardware conflicts while you are doing your research. Look for hardware that has known conflicts with what you are looking for.
I am into the AMD setups mostly and will review the website's offerings for motherboard/memory combinations and do a simple websearch for the cons on that system's configuration. If during your research you found a "must-have" item for your system, make sure its compatible with the rest of the parts. You can do this by matching them to the motherboard specifications. This can be the processor type and speed or the type of drive connections you need (SATA/RAID or SSD). For the gaming community, the SSD seems to be the way to go, with no physical hardware connections to "read" and near instant response times.
My AMD system consists of the following:
3.6Ghz AMD processor, with LED color changing coolant system.
16G RAM
8G Video card
1TB SSD card
Dual 1TB SATA drives running RAID 0 (striped together).
The case has been hacked apart to fit the coolant system and it still gets way too hot so the side cover is never on. Try building a new system using the manufacturer's website (like Dell). Select a high-end product and strip out the things you dont need. I was able to reduce a $5000 Dell system to under $2000 after removing all the fluff. It may not run as fast as the $5000 one, but I'd bet it would be close. Its also a lot faster than anything I am currently running.