Cases are usually broken up into two different forms (ATX and AT). You must make sure that the case and motherboard are the same form. ATX allows for the motherboard to be installed at a 90 degree rotation. The case has the primary functions of housing, ventilating, powering, and blocking the transmissions of EMF's. Most cases come with screws, case feet, power cord, and expansion inserts. The power supply is commonly installed with the case. Look for a 300 watt power supply for future upgrades to your pc.
The ATX form factor was invented by Intel in 1995. ATX and its similar models (Mini ATX) have now become the industry standard. The ATX case is similar to a Baby AT case except that the holes in the back are altered to fit the changed design of the ATX form factor motherboard, in particular the integrated I/O ports. Intel has also specified a "Mini ATX" motherboard size, which is slightly smaller than the full-sized ATX specification. These boards use the same ATX form factor power supplies and cases. The main difference is that full ATX motherboards have a maximum size of 12"x9.6", and Mini ATX boards have maximum dimensions of 11.2"x8.2".You may also come across motherboards, particularly high-end models used in performance workstations or servers, that use the "Extended ATX" form factor. This form factor is essentially the same as ATX, except that the board can be up to 12"x13" in size. These boards are uncommon, and the Extended ATX form factor is likely to receive significant competition from the new WTX form factor, which was designed especially for workstations.
The ATX power supply design differs from the previous market standards, the Baby AT and LPX form factors, in several important ways: .
True Standard: The ATX form factor is a standard, as opposed to the differing designs of prior form factors. .
+3.3 V Power: ATX systems were the first to include +3.3 V power directly, avoiding the need for voltage regulators to provide it on the motherboard.