The motherboard is the backbone of a computer, connecting everything together.
While it contains many components, they are standard and will be found in essentially all computers.
Instead, a set of sockets are provided for these components.
This design actually comes with several advantages.
The main advantage is the choice of the end user.
Suppose the motherboard had the RAM, CPU, and GPU all baked directly onto the motherboard.
In that case, thered have to be many motherboards from each manufacturer.
It also allows for future upgrades, as the parts can be easily swapped.
Another advantage of providing connectors is that daughterboards can be used that stick up further into clean air.
This helps to keep some components like RAM and GPUs cool.
Technically, some of the sockets on the motherboard arent considered expansion slots.
These are generally single purposes, such as the CPU socket, RAM sockets, and M.2 slots.
General purpose slots, though, are usually referred to as expansion slots.
AGP or Accelerated Graphics Port was an expansion slot for graphics cards in the late 90s and early 00s.
It is now defunct and not present on modern motherboards.
The VESA connector was another expansion port for video cards.
AMR was an expansion slot for audio and/or modem cards.
The Audio Modem Riser was designed in 1998 to support one or both functions.
However, it never saw much adoption.
In 2000 the AMR standard was revised into the Communications and web link Riser, or CNR.
It offered audio, modem, USB, and LAN connectivity.
The Advanced Communications Riser, or ACR, was a competing standard that retained backward compatibility with AMR.
None of these technologies remain in use as all functionality has now been integrated onto the motherboard.
ISA or Industry Standard Architecture was the original expansion slot for the IBM PC in 1984.
However, the name is actually a retronym.
In 1987 IBM attempted to replace it with the proprietary Micro Channel Architecture or MCA.
Other computer manufacturers countered by trying to standardize the Extended Industry Standard Architecture.
However, neither caught on.
Expansion Slots The Present
PCI or Peripheral Component Interconnect was an expansion slot defined in 1992.
It was a general purpose and relatively high-speed for the time.
However, this didnt see much use in the consumer market.
PCI and PCI-X were superseded in 2002 with the release of PCIe, also known as PCI Express.
PCIe offered high-speed complete duplex transmission with a configurable number of lanes depending on the overall bandwidth desired.
PCIe quickly became the dominant expansion slot.
Today essentially all motherboards exclusively use PCIe expansion slots.
PCIe has seen several revisions, with PCIe Gen 5 just starting to make its way to market.
This makes it ideal for connecting modern graphics cards, which need a lot of bandwidth.
The PCIe bus and, in some cases, PCIe expansion slots are also used for high-speed SSDs.
A modern standard ATX motherboard will have four 16x PCIe slots.
However, there may also be several smaller ones.
not all physical 16x PCIe slots are connected with 166 logical PCIe lanes.
These expansion cards typically provide hardware for a specific function, though some can be multi-function.
The expansion slot itself usually allows for a range of cards and functions of those cards.
In modern motherboards, expansion slots are exclusively PCIe slots and utilize the PCIe bus.
Other expansion slots and busses have been superseded and are now legacy or completely unsupported.
The primary use for expansion slots in modern computers is for discrete graphics cards.
