Port expander

Lore & Background

Two basic forms of port expander exist: internal and external. An internal expander has a connection inside the computer, typically on the motherboard, and the only part the user sees is the expansion plate containing multiple ports. An external device plugs into the existing port and then has multiple places to connect. When not part of a computer system, these devices are commonly known as splitters.

In the non-computer world, splitters are very common. Extension cords and power strips split a single outlet to multiple devices. Cable splitters allow a single coaxial cable to provide cable television to multiple sets. Some systems may even use an A/B box, a device that connects multiple sets of devices to the same system, with users switching between them by flipping between the A or B mode.

Manufacturers have produced expanders for nearly every type of port, but the most common household versions connect to universal serial bus (USB) or to Ethernet ports. The VIC-20, for example, used a port expander to allow more than one cartridge to connect to the single ROM cartridge port.

Reader's Guide

A major downside of a port expander is that bandwidth is shared among connected devices. For example, a 3 Gbit/s port might have a hub or expander installed and now be able to accommodate 6 devices, but at a maximum of 3 Gbit/s throughput bandwidth divided by the said 6 devices, or by however many are plugged in and being used. This bandwidth limitation is a key consideration when using expanders for high-throughput applications.

Port expanders perform the same basic job as splitters in other domains: they connect to a single spot but have multiple connections for devices. They go by several names, such as "switch", "hub" or "splitter", but they all do the same thing. Their significance lies in enabling a computer system to connect to multiple peripherals through a single port, expanding the system's capabilities without requiring additional onboard ports. This is especially useful for legacy systems like the VIC-20, which had only one cartridge port, or for modern systems where users need to connect many USB or Ethernet devices to a limited number of ports.

Did You Know?

• A port expander can be any device to which one existing or onboard port becomes two or more, such as a KVM switch or a USB hub.
• A major downside is that bandwidth is divided among connected devices; for example, a 3 Gbit/s port with 6 devices yields a maximum of 3 Gbit/s shared throughput.