ProLiant is a brand of server computers that was originally developed and marketed by Compaq. After Compaq merged with Hewlett-Packard (HP), HP retired its Netserver brand in favor of the ProLiant brand. The brand is currently marketed by Hewlett Packard Enterprise. HP ProLiant systems led the x86server market in terms of units and revenue during first quarter of 2010.

ProLiant servers are separated into four main product lines – ML, DL, BL, and SL – which generally denote form factor. The ProLiant ML line comprises tower-based servers (convertible to rack mount) with capacity for internal expansion of disks and interconnects, while the DL line comprises general purpose rack mount servers. The BL line comprises blade servers which fit within the HP BladeSystem, and the SL line comprises dense rack mount servers for scale out environments. The MicroServer product line addresses small and home businesses

The main difference between a tower server and a rack server is how theservers are placed. A tower server is built in a cabinet, while a rack server has a huge rack that is built with bays to store multiple servers. A tower server can also be mounted in a rack in a special room, allowing it to take up less space