Computer hardware cases come in a variety of sizes from full-tower to small form factor. Full-tower cases are the largest with heights over 30 inches and 6 to 10 internal drive bays. Mid-tower cases are most common, standing 18 to 24 inches tall with 2 to 4 drive bays. Mini-tower cases are shorter at 12 to 18 inches but have limited expandability with only 2 or 3 drive bays. Small form factor cases minimize the computer's volume and come in various small sizes and shapes.