I'm thinking about building a new, modern PC to replace my aging Dell Dimension 8200. I would like it to be an ATX, like the Dell, and to place it on the same computer hutch the old machine sits on.
Unfortunately, I've noticed that cases seem to have increased in size, especially in depth, over the years. The old machine, at 7.13"W X 17.6"D X 16.7"H just fits in its space, with about an inch or two of wiggle room in depth. The space itself is 15W X 19D X 20H, but I need room for cables etc. The back has air flow slots, but it does not come completely out.
Well hardware is hot and its getting bigger.
-CPU coolers are getting massive and water cooling is also popular which requires tons of space for tubing...etc
-Videocards are getting huge, new ones released are are 10''+...some are even a 1 foot long lol
-Plus large cases are easier to build in and have more room for expansion like storage and hardware.
What is your build going to consist of, MB/GPU, will you need an after market HSF (Intel's HSF are not the Greatest), Can you use a micro atx MB ??
What do you use the computer for, Do you what great frame rate in the lates games??, or is this mainly for video work.
For Gaming, and with the higher end GPU's You need the larger case as Johnny pointed out and also for better airflow in side the case. As to keyboard/mouse, how about wireless. Picked up a cheapy, of all places Biglots normally $40, for $26. NOT the Best (poor for gaming). Replaced a >$100 bluetooth.
Because components are bigger, better, faster, stronger.... Also, some people just like things big, like their gas guzzling SUVs.
Anyway bigger cases with more fans help with ventilation. Size isn't everything in this regard as a big case can still have crappy air flow if it's of a poor design. Also, gaming GPUs have gotten bigger (like the 5970), and bigger cases are also needed for big tower coolers used in overclocking CPUs. If you aren't going to use a big heatsink or a big GPU, then you may be fine with a smaller case like the ones suggested above.