As a player levels up, they can purchase better CPUs, Hard Drives, and Memory for their computer from the Store in the Web Browser application. You can also receive PCI and AGP cards from NPC drops, or purchase them from other players/the game store -- these cards give you various other bonuses: extra damage, extra CPU points, immunities, etc. To equip your hardware go to System->Administration->Equipment Manager

CPUs

Every application, watch, or firewall that a player installs takes a certain portion of CPU load. As a player levels up they can purchase better CPUs to allow them to run more applications simultaneously.

Hard Drives

A player can only store a limited number of files on their hard drive (this includes their Store and Public directories). As a player levels up they can purchase better Hard Drives to increase the amount of space available.

Memory

By purchasing better memory, a player can install applications on a larger range of ports (to start out a player only has 8 ports to install applications on). Memory also determines how many watches you can have running at any given time.

PCI/AGP Cards

Additional upgrades for your computer (in the form of PCI and AGP cards) are dropped by NPCs. They can be purchased from the game store, or from other players.