Cable Types, Connectors,
Features & Purposes

OVERVIEWIntroduction

Cables and connectors are the physical foundation of every computing environment — data, video, storage, and power all travel through cables between components. An IT technician who can immediately identify a connector type, understand its capabilities and limitations, and choose the correct cable for a given application is far more effective in the field than one who must look up each connector individually.

Objective 3.2 covers four categories of cables (network, peripheral, video, storage), adapters, and a specific list of connector types you must be able to identify by name and physical description. This section covers all of them with enough depth to handle scenario-based exam questions.

SECTION 1Network Cables — Copper

Copper network cables are the backbone of wired local area networks. They transmit data electrically through copper conductors and are the standard connection method for desktop computers, network switches, routers, and any device that requires a reliable, low-latency wired connection.

Twisted Pair Cable Categories

Twisted pair Ethernet cables consist of four pairs of copper wires — eight wires total. Each pair is twisted together at a specific rate per foot, which reduces crosstalk (electromagnetic interference between adjacent wire pairs) and EMI (external electromagnetic interference). The tighter the twist rate, the better the interference rejection, and the higher the supported data rate.

Cables are categorized (Cat) by their electrical performance specifications. Higher category numbers support higher frequencies, faster data rates, and longer distances at speed:

T568A and T568B Wiring Standards

The T568A and T568B standards define the specific order in which the eight wires of an Ethernet cable are inserted into an RJ-45 connector. Both standards produce functional cables — they differ only in which pairs are assigned to pins 1–2 and 3–6. The standards are defined by TIA/EIA-568 and determine whether a cable is a straight-through cable or a crossover cable.

Shielded Twisted Pair (STP) and Unshielded Twisted Pair (UTP)

Coaxial Cable

Coaxial cable (coax) has a very different construction from twisted pair: a single central copper conductor, surrounded by a dielectric insulator, surrounded by a woven copper mesh shield, surrounded by an outer plastic jacket — all concentric (sharing the same axis, hence "co-axial"). The shield completely surrounds the signal conductor, making coax inherently immune to most EMI.

Plenum-Rated Cable

Plenum refers to the air space inside a building used for HVAC air circulation — specifically the space above drop ceilings and below raised floors. In many commercial buildings, network cables are routed through these plenum spaces.

Standard PVC cable jacket material releases toxic chlorine gas when burned. In an enclosed air-handling space, burning standard cable in a fire would rapidly distribute toxic fumes throughout the entire building via the HVAC system. Plenum-rated cable (CMP — Communications Multipurpose Plenum) uses a low-smoke, low-toxicity jacket material (typically fluoropolymer or flame-retardant PVC) that self-extinguishes and releases minimal toxic fumes when exposed to fire.

The cable jacket rating hierarchy (from most to least restrictive installation environment): CMP (Plenum) > CMR (Riser — between floors in conduit, non-plenum) > CM (General Purpose — same floor) > CMX (Residential).

SECTION 2Network Cables — Optical Fiber

Fiber optic cable transmits data as pulses of light rather than electrical signals through copper. A glass or plastic core carries light from a laser or LED source at one end to a photodetector at the other. Because light is immune to electromagnetic interference and can travel much longer distances than electrical signals without significant degradation, fiber optic cable is used for long-distance runs, high-bandwidth connections, and any environment where EMI is a concern.

Single-Mode Fiber (SMF)

Single-mode fiber has a very narrow core — approximately 8–10 µm in diameter (about the width of a human hair). The narrow core allows only a single propagation mode of light (a single "path" or "ray") to travel through the fiber. Because all light travels the same path, there is no modal dispersion (light arriving at slightly different times via different paths). Single-mode fiber can carry signals over extremely long distances — tens of kilometers — with minimal signal degradation.

• Core diameter: ~8–10 µm
• Light source: laser diode (coherent light; expensive)
• Typical distance: 10–100+ km without repeaters
• Color coding: yellow jacket (OS1/OS2 standards)
• Use cases: long-haul telecommunications, ISP backbone, campus networks spanning multiple buildings, metropolitan area networks
• Cost: higher than multimode due to precision manufacturing and laser transceivers

Multimode Fiber (MMF)

Multimode fiber has a larger core — 50 µm or 62.5 µm in diameter. The larger core allows multiple propagation modes (multiple light paths at slightly different angles) to travel simultaneously. This causes modal dispersion — light rays traveling different paths arrive at slightly different times, spreading the signal pulse over time and limiting transmission distance and data rate. Multimode is less expensive than single-mode and uses LEDs or VCSELs rather than precision lasers.

• Core diameter: 50 µm (OM3/OM4/OM5) or 62.5 µm (OM1/OM2, legacy)
• Light source: LED or VCSEL (Vertical Cavity Surface Emitting Laser)
• Typical distance: up to 550m for 10G on OM3; up to 400m for 10G on OM4
• Color coding: orange (OM1/OM2), aqua (OM3), violet/erika (OM4), lime green (OM5)
• Use cases: data center interconnects, within-building backbone, SAN connections, high-speed LAN
• Cost: lower than single-mode; LEDs and VCSELs are cheaper than precision laser transceivers

SECTION 3Peripheral Cables

USB (Universal Serial Bus)

USB is the universal standard for connecting peripherals — keyboards, mice, storage drives, printers, cameras, and hundreds of other device types — to computers. USB has gone through multiple major revisions, each increasing data transfer speed. Understanding the version numbering is critical because USB has been renamed multiple times, creating significant confusion.

Serial (RS-232 / DB-9)

Serial in the context of legacy peripheral connections refers to the RS-232 standard, using the DB-9 (DE-9) connector — a 9-pin D-shaped connector. Serial transmits data one bit at a time over a single wire, at low speeds (typically 9600 baud to 115,200 baud). Once the universal standard for modems, mice, and external devices, serial was almost entirely replaced by USB.

Serial ports survive in specific use cases: configuring network routers and switches via console port (Cisco, Juniper), industrial control systems (PLCs, CNC machines), scientific instruments, and serial-controlled devices in manufacturing. A USB-to-serial adapter allows modern laptops without serial ports to communicate with these legacy devices.

Thunderbolt

Thunderbolt is a high-speed interface developed by Intel in collaboration with Apple. It combines multiple protocols — PCIe (for high-performance data and external GPU), DisplayPort (for video), and USB — into a single cable and connector. The Thunderbolt symbol (⚡) is printed next to compatible ports.

SECTION 4Video Cables

VGA (Video Graphics Array)

VGA is the oldest display standard still in use, introduced with the IBM PS/2 in 1987. It uses a 15-pin D-subminiature (DB-15 or HD-15) connector — three rows of five pins in a trapezoidal shell. VGA is an analog signal — the video data is transmitted as continuous voltage variations representing color intensity, not as digital data. This is a fundamental limitation: analog signals degrade with cable length, are susceptible to interference, and cannot achieve the sharp pixel-perfect image of digital connections at high resolutions.

• Signal type: analog RGB
• Audio: no audio signal carried
• Maximum resolution: technically unlimited (analog), but practical limit ~2560×1600; quality degrades at higher resolutions
• Connector: DB-15 (HD-15), blue color coding by convention
• Current status: legacy; found on projectors, older monitors, older laptops. Being phased out completely.

DVI (Digital Visual Interface)

DVI was designed to succeed VGA as the primary computer monitor connection, offering digital signal transmission. DVI uses a wide rectangular connector that comes in several variants, distinguished by their pin arrangements:

DVI carries no audio. It is largely superseded by HDMI and DisplayPort but still found on older monitors and graphics cards. A key exam point: DVI-I adapts to VGA (because it carries analog pins); DVI-D does not adapt to VGA without an active converter.

HDMI (High-Definition Multimedia Interface)

HDMI is the dominant consumer display standard, carrying both high-definition video and multi-channel audio on a single cable. The familiar HDMI connector — a 19-pin trapezoidal connector — is found on televisions, monitors, laptops, gaming consoles, streaming devices, and AV equipment.

HDMI connector form factors: Standard HDMI (Type A, full size), Mini HDMI (Type C, smaller devices), Micro HDMI (Type D, cameras, tablets). The full-size standard connector is most common in the exam context.

DisplayPort

DisplayPort is a digital display interface developed by VESA, designed specifically for connecting computers to monitors. Unlike HDMI (which originated in the consumer electronics industry), DisplayPort was designed from the start for computer display applications. It supports higher refresh rates than HDMI at the same version level and is the preferred connection for high-refresh-rate gaming monitors and multi-monitor setups.

USB-C as a Video Connector

USB-C supports Alternate Mode (Alt Mode) — the ability to carry non-USB signals through its pins. When a device and cable support DisplayPort Alt Mode, the USB-C port carries a full DisplayPort signal, enabling video output without a separate DisplayPort connector. Thunderbolt 3/4 ports also carry DisplayPort natively. Not all USB-C ports support video output — a USB-C port that only implements USB power delivery will not carry video.

SECTION 5Hard Drive Cables

SATA (Serial Advanced Technology Attachment)

SATA is the standard interface connecting storage drives (HDDs and SSDs) to the motherboard inside a computer. SATA replaced the older PATA/IDE (Parallel ATA) standard, offering higher speeds, a much smaller connector, thinner cables (improving airflow), and hot-swapping capability.

eSATA (External SATA)

eSATA extends the SATA interface for external drive connections. The eSATA connector is a modified SATA connector — similar shape but with reinforced contacts designed for repeated insertion/removal and without the data and power combined in one plug (eSATA is data-only; external power is required separately or via eSATAp which adds USB power). eSATA provides SATA III speeds (6 Gbps) to external drives — faster than USB 2.0 and early USB 3.0 when those were the alternatives.

eSATA has been largely superseded by USB 3.0 and USB 3.1 Gen 2 (10 Gbps), which are faster, provide power, and are more universally supported. eSATA ports are still found on some older desktop and laptop systems. The maximum cable length for eSATA is 2 meters (vs. 1 meter for internal SATA).

SECTION 6Adapters

Adapters convert one connector type to another, enabling connectivity between devices that use different interface standards. Understanding when a passive adapter works versus when an active (powered) converter is required is critical — using the wrong type can result in no signal or a damaged device.

SECTION 7Connector Types — Identification Reference

The A+ exam requires identifying connectors by name and physical description. This section covers every connector listed in the official objectives with enough detail to answer identification questions.

Connector Quick-Reference Table