ISA coloured black (Industry Standard Architecture) ran at 8mbps was located on the Southbridge. It is obsolete now
PCI (Peripheral Component Interconnect) is plug and play. It has the lowest speed. It is coloured white and runs at 133mbps. It rendered the old ISA expansion slot (coloured black) obsolete. Used for network, sound, modems and usb and serial ports. PCI video cards are used to support extra monitors and upgrading PCs that do not have any PCIe or AGP slots. Many devices That used to be provided on expansion cards are now integrated onto the mobo itself, meaning that modern PCs often have no cards fitted. However, PCI is still used for certain specialized cards but many jobs that were performed by expansion cards may now be performed equally well by USB devices.
AGP is accelerated graphics and connects video directly to memory, it is dark brown and runs at 2 GBPS. There is only one in a system. It is located on the northbridge on the motherboard. It is a high speed channel for directly connecting the video to the mobo.It was used for 3D graphics and has been phased out for PCIe.
PCIe (express) is the fastest and is usually yellow and runs at 16GBPS.It has dual line technology that means 8 gbps of data up and down at the same time. Best for gaming photography and video. It has a 164 pin slot. The most common slot found in modern desktops.