The back panel of a computer contains ports used to connect different peripherals that depend on the applications in use. Some of the devices that can plug into the ports include scanners, printers, cameras, speakers, microphones and game controllers, just to mention a few. VGA/DVI connectors are used to connect to other display devices while HDMI provides a connection to HD displays or TVs. The eSATA port is for connecting a computer to an external SATA hard drive. There is also an Ethernet port on a PC back panel that allows connections to the internet. Most computers have extra USB ports that are available at the back for instances when users need to use more devices.
Uniformity in Design
Most computers come with a uniform back panel because there is a need to maintain standards during manufacturing. A PC back panel may look like a bunch of cables and wires bundled together, but there is a system to the chaos. Currently, the ATX form factor is the one in use, and it offers three sections of the back panel layout. The top part of the panel holds the power supply, I/O connectors in the middle and the bottom part has the expansion board slots.
Old Model Issues
Over the years, technology advances have resulted in many changes that had an impact on computer standards. It is why old back panel models present a challenge because they fail to meet some of these standards. You may find that older machines have obsolete interface connectors, thus, presenting configuration problems.
Industrial PCs Back Panels
The design of an industrial computer must match the back panel model in use for proper operation. Industrial PCs are engineered to meet specific applications; and therefore, require the right connectors. The ports on the back panel of an industrial PC must correspond in shape and size to the cables connecting different devices. Plugging in the wrong port can cause a machine to blow up.
Computer Ports and Their Functions, hubpages.com
An Introduction to your Computer, bleepingcomputer.com