ATX PCs
ATX, or Advanced Technology Extended (yes, we had to look that up!) is the ‘standard’ sized PC. A small tower which is bigger than ITX but much smaller than E-ATX or full towers.
ATX allows your PC to have enough space to fit almost any component but also gives you enough room for your PC to have good airflow.
Unless you specifically need something bigger or smaller, ATX is usually the correct size PC.