Proprietary computers are made from machine components ready-made next to the same chipset, such as as the Intel P35, but not made in the ensign form, very normative ATX motherboards. The motherboards in abundant patented systems such as as Dells and Gateways are made one and only to proceedings the particular weaponry in the computing device. So in plain words, you won't have 6 SATA ports, i don't know 1 or no surplus PCI slots, noticeably not an standby PCIe x16 slot, or any separate extras that come with beside normative ATX way cause motherboards.
Why do they do this? Because those companies poverty to check you to the data processor weapons system that comes beside the systems. They deprivation you to second on them, and go support and buy other one of their patented systems. This fundamentally trumps any of your upgrading aspirations, and prevents you from conformity with the same at-large set-up for a extended incident but rightful rise several components.