EMZETT.Ports
In short: Physical interfaces on a device through which cables or peripherals are connected — e.g. USB, HDMI, network or audio jacks.
In more detail: The type and number of available ports determines which peripherals can be used directly, without resorting to adapters or docking stations. On a motherboard’s I/O panel, or on the back of the case, most ports are accessible bundled together.
In Depth
Where ports sit
Which ports a device comes with directly decides what can be connected without extra hardware. On desktop motherboards, most of them sit bundled on the I/O panel: USB jacks in various generations and form factors (USB-A, USB-C), a network jack (RJ45 for Ethernet), audio jacks, and depending on the configuration, DisplayPort or HDMI for a graphics unit integrated into the CPU. Additional internal connectors (e.g. for SATA drives, case fans, front-panel USB) sit directly on the board and aren’t visible from outside. On laptops, and especially very thin ultrabooks, the number is deliberately reduced to save space and weight — here docking stations or USB-C hubs make up for the missing variety by fanning a single USB-C port out into several legacy ports.
Port type vs. protocol
An important, often overlooked difference is that between the port type (the connector shape, e.g. USB-C) and the protocol running over it (e.g. USB 3.2, DisplayPort Alt Mode, Thunderbolt). The same jack can support completely different speeds and functions depending on the chipset installed and the internal wiring. A USB-C port without Thunderbolt support, for example, charges a notebook just the same, but can’t drive an external monitor via DisplayPort Alt Mode, and often only delivers a fraction of the data rate of a full-fledged Thunderbolt port. Manufacturers rarely mark this difference clearly on the device itself — a look at the technical datasheet is therefore often essential when buying, if a particular function (e.g. an external monitor, a fast external SSD) matters.
Categories of ports
Roughly, ports can be divided into three categories: data ports (USB, Ethernet, SATA), video ports (HDMI, DisplayPort, VGA as a discontinued model), and pure power ports (power supply jacks, sometimes also delivered via USB-C through Power Delivery). Many modern ports like USB-C now combine several of these categories at once in a single physical connector, which makes devices more compact, but dissolves the clear mapping “one connector type = one function” that earlier generations of hardware still had.
Backward compatibility and adapters
Many older port types (e.g. VGA, classic USB-A) can still be used with modern hardware via adapters, though often with a loss of quality or functionality — a VGA-to-HDMI adapter, for example, has to actively convert the analogue VGA signal into a digital HDMI signal, which requires extra electronics in the adapter and, depending on quality, can lead to image problems. Purely “passive” adapters (without their own conversion electronics), by contrast, only work between electrically compatible standards.
See also: I/O panel, USB, HDMI, DisplayPort, Peripherals