PC Cases - Hardware - Different Case Styles TOWER: A HUGE case, and is usually only reserved for the most demanding applications, such as a server, these cases have room for more than a half dozen disk drives. MID-TOWER: This is by far the most popular choice for the Build-It-Yourself. It stands upright and usually has about Four Drive Bays and Six Expansion Slots-just right for most people. MINI-TOWER: For those who don't need extensive expansion and have size needs. this model is a popular choice. DESKTOP: Once the most popular style it's overly bulky look and limited expansion capability have caused it to lose favour to the more hide able towers. BAYS There are two kinds of bays. Those with Front Panel Access and those without.  Front Panel Access bays are for devices using removable media (i.e.. CD-Rom Drives, Floppy Drives etc.). They have an opening at the front of the case to be able to slide in or out a disk. An Internal Bay has no front panel access and is built just below the bays with Front Panel Access. This Bay is primarily used for the computers Hard Disk Drive.