CompTIA A+ Core 1: Basic Cable Types, Connectors, Features, and Purposes Explained

1. Why Cable Knowledge Matters for A+ Technicians

For CompTIA A+ Core 1 (220-1101), cable questions are mostly about being able to look at a cable or connector and quickly figure out what it is, what it’ll work with, and where the physical connection might be going wrong. In the real world, a lot of “device failures” end up being something a whole lot simpler: a loose connector, the wrong cable, a patch cord that’s worn out, or an adapter that fits perfectly but can’t actually handle the signal you need. Good techs usually check the cable path early, before they go chasing some bigger mystery that turns out to be a loose plug or a bad cord. My usual first pass is pretty straightforward: identify the connector, look for obvious damage, make sure the port actually supports what you’re trying to do, and try a known-good cable before you start blaming the hardware.

Honestly, that same approach helps a lot on the exam too. You don’t need to be a cabling engineer, but you do need to recognize the common cable families, know what they plug into, and dodge the usual traps—like confusing phone and Ethernet connectors, assuming every USB-C cable behaves the same way, or acting like analog and digital video are basically the same thing.

2. Twisted-Pair Ethernet: the cable family you’ll probably see most often, plus the connectors and terms you really need to know

Twisted-pair Ethernet is basically the wired network cable you’ll run into all the time in support work — desktops, printers, switches, routers, access points, wall jacks, all of it. The plug on Ethernet patch cables is commonly called RJ-45, but the more precise term is an 8P8C modular connector. Likewise, phone connectors are commonly called RJ-11, though that is shorthand for smaller 6-position modular connectors used for telephone service. For A+, the shorthand is usually fine, but knowing what’s actually what keeps you sharp and helps you avoid those sneaky exam traps.

Most Ethernet cabling in offices uses UTP, or unshielded twisted pair. STP, or shielded twisted pair, is used when electromagnetic or radio-frequency interference is a concern. The important thing to remember is that shielding only really helps if the whole setup is done properly, with compatible shielded parts and correct grounding or bonding. If shielding’s done badly, it usually just adds cost without solving much.

For category ratings, keep these exam-safe facts in mind: Cat 5e supports 1 Gbps up to 100 meters, Cat 6 supports 1 Gbps up to 100 meters and 10 Gbps only over shorter distances, commonly up to about 55 meters depending on conditions, and Cat 6a supports 10 Gbps up to 100 meters. Cat 7 might come up in conversation, but it’s not a major A+ focus and it’s not the usual endpoint choice the way Cat 5e, Cat 6, and Cat 6a are. Cat 8 exists mainly for short, very high-speed data center use.

The standard Ethernet channel limit is 100 meters total: typically 90 meters permanent link in the walls plus up to 10 meters of patch cords. That's a really useful number for both the exam and real-world troubleshooting.

Another practical distinction is solid-core versus stranded conductor cable. Solid-core cable is commonly used for horizontal building runs and punchdown terminations. Stranded cable is more flexible and is typically used for patch cords. You generally do not want to substitute a cheap patch cable for a permanent in-wall run.

T568A and T568B are the two common pinout standards for terminating Ethernet. The big exam idea is consistency: if you want a straight-through cable, wire both ends the same way. A crossover cable uses different standards on opposite ends. The color orders are:

T568A: white/green, green, white/orange, blue, white/blue, orange, white/brown, brown

T568B: white/orange, orange, white/green, blue, white/blue, green, white/brown, brown

Straight-through is the normal choice when you’re connecting an endpoint to a switch. Crossover was historically used for like-to-like connections such as PC-to-PC or switch-to-switch, but modern gear usually supports auto MDI-X, so manual crossover concerns are now mostly legacy. Still, CompTIA absolutely expects you to know the concept and recognize it on sight.

PoE, or Power over Ethernet, allows a compatible switch or injector to send power and data over the same Ethernet cable. The PoE devices I see most often are IP phones, wireless access points, and IP cameras. Those are the usual suspects in most office and campus environments. Honestly, those are usually the first things I’d check. At a recognition level, know 802.3af (PoE), 802.3at (PoE+), and 802.3bt (higher power, often called PoE++). Not every switch port supports PoE, and the device on the other end has to be able to take power that way too — otherwise it’s not going to help much. If it can’t, then you’ll need the correct injector or splitter to make it work. That’s one of those tiny details that catches people all the time, even when they’ve got the rest of the setup right.

If an access point won’t power on, I’d start by checking whether the switch port actually supports PoE, whether PoE is enabled, whether the cable is in good shape, and whether the device needs more power than that port can provide. A link light with flaky device behavior can point to not enough power instead of bad networking.

Most testable facts: 8P8C is the Ethernet plug commonly called RJ-45, Cat 6 does not automatically mean 10 Gb to 100 m, T568A and T568B must be used consistently, and PoE requires compatible equipment.

3. Coaxial cabling is the older-style cable you’ll still see a lot for internet, TV, and some video systems.

Coaxial cable is a copper cable with a center conductor, insulation, shielding, and an outer jacket, all built around keeping the signal stable. It’s widely used for RF distribution, cable internet, television service, and some CCTV or legacy video systems. For A+, the two most common connector clues are F-type and BNC. F-type connectors screw on and are common on cable modems and TVs. BNC connectors use a twist-lock mechanism and are common in CCTV, test equipment, and some legacy contexts, including older Ethernet references such as 10BASE2 in historical material.

RG-6 is the common modern choice for cable TV and cable internet. RG-59 is more associated with older video and shorter-run applications. They are not interchangeable in every scenario just because both are coax.

A basic cable internet path is wall coax jack → splitter if present → cable modem → Ethernet to router or PC. If a modem has power but no service, the coax run is the first thing I’d check. Make sure the F-type connector is tightened all the way, look for damaged splitters, and confirm the modem is connected to the active provider feed. Too many splitters, or just bad-quality splitters, can weaken the signal enough to cause sync problems.

At a basic support level, modem lights matter. A blinking or failed online/status light usually means the modem isn’t syncing properly with the service provider. In a case like that, the Ethernet cable to the router could be perfectly fine, and the real issue might actually be farther upstream on the coax side.

Most testable facts: F-type screws on, BNC twists and locks, RG-6 is the common modern cable-service choice, and a cable modem depends on a working coax feed.

4. Fiber Optics: SMF, MMF, Connectors, Optics, and Safety

Fiber-optic cable carries data as light, so it’s a great fit for long distances, high bandwidth, and places with a lot of electrical noise. Its major A+ advantages are distance and immunity to EMI. The key distinction is single-mode fiber (SMF) for longer distances and multimode fiber (MMF) for shorter runs such as within buildings.

The common connectors to recognize are LC, SC, and ST. LC is the small, compact connector, SC is the square-shaped one, and ST is the round connector with that twist-and-lock, bayonet-style fit. Fiber links may use fixed ports or pluggable optics such as SFP or SFP+, but remember that not all SFP-family modules are fiber; some are copper.

The most important technical rule is compatibility: a working fiber link requires the correct fiber type, optic or transceiver type, wavelength, speed, and connector. SMF and MMF are not interchangeable, and duplex fiber also requires correct TX/RX polarity. If transmit and receive are crossed the wrong way, the link just won’t come up.

Fiber handling matters. Never look directly into a fiber end or transceiver. Invisible laser light can still be present even when everything looks completely powered off, and that’s not something you want to gamble with. Keep dust caps on unused ports, avoid tight bends, and clean connectors with proper fiber-cleaning tools. A dirty fiber end can make a link fail or act flaky even when the cable looks totally fine from the outside.

If a building uplink drops right after someone swaps a patch cord, I’d start with the usual suspects: an MMF patch cable on an SMF link, the wrong SFP type, a dirty connector, or a reversed duplex pair. Those are much more common than a dead switch.

Most testable facts: SMF is for longer distances, MMF is for shorter distances, LC is small, SC is square, ST twists to lock, and fiber type plus optics must match.

5. USB, USB-C, Lightning, and Thunderbolt are the ports and cables that cause a ton of “but it fits, so why doesn’t it work?” confusion.

USB shows up everywhere — peripherals, storage, charging, docking, and sometimes even video output. The biggest exam trap is this: connector shape does not guarantee capability. That matters most with USB-C.

Recognize these connector families: USB-A is the classic rectangular connector, USB-B is commonly used on printers, Mini-USB and Micro-USB are older small-device connectors, and USB-C is the small oval reversible connector now common on laptops, phones, docks, and drives. Lightning is Apple’s proprietary connector used on older iPhones and accessories.

With USB-C, separate these ideas in your head: connector form factor, USB data standard such as USB 2.0, USB 3.x, or USB4, USB Power Delivery for charging, DisplayPort Alt Mode for video, and Thunderbolt. A USB-C cable or port may support some of those and not others. Some higher-power or higher-speed USB-C cables include e-marker chips to identify capabilities.

Thunderbolt 3 and 4 use USB-C connectors, but earlier Thunderbolt versions used Mini DisplayPort-shaped connectors. In support work, I always treat Thunderbolt as something to verify instead of assuming it’s supported just because the port shape looks right.

If a USB printer using a normal USB-A to USB-B cable isn’t being recognized, the usual suspects are a bad cable, a bad USB port, a flaky hub, missing drivers, or a disabled USB controller. “Charge-only cable” is a common phone-cable problem, not a typical explanation for standard USB printer cables.

A very common modern scenario is a laptop that charges just fine over USB-C but still won’t send video to an external monitor. That usually means one of a few things: there’s no DisplayPort Alt Mode support, the dock doesn’t support the feature, the cable isn’t the right type, or the port handles charging and data but not video.

Most testable facts: USB-C is a shape, not a promise; USB-B is common on printers; Lightning is Apple-specific; Thunderbolt 3 and 4 use USB-C; and charging support does not guarantee video support.

6. Video and Display Cables: the digital and analog standards you’ll see most often

For A+, know the difference between digital and analog video. HDMI and DisplayPort are digital. VGA is analog and uses the familiar DE-15/HD-15 connector with three rows of pins and screw posts. DVI comes in variants: DVI-D is digital only, DVI-A is analog only, and DVI-I can carry both.

HDMI shows up all over the place — TVs, projectors, and a lot of monitors too. DisplayPort is very common in business environments, especially on desktops, office monitors, and docking stations. One reason DisplayPort shows up often in workstation environments is support for features such as MST, or Multi-Stream Transport, on compatible hardware for daisy-chaining or multi-monitor setups.

The key adapter rule is signal conversion. Going from digital sources like HDMI or DisplayPort to analog VGA often requires an active converter. A passive adapter only works when the source port actually provides a compatible signal, which many modern devices do not. This is why “the plug fits” is not enough.

If someone plugs a modern laptop into an old VGA projector, you’ve got to choose the adapter carefully and be realistic about possible resolution limits. If a 4K monitor only shows up at 1080p through a dock, I’d start by checking the dock’s display bandwidth, the quality of the cable, the output standard, and whether the whole adapter chain actually supports the resolution and refresh rate you’re expecting. In some setups, EDID or HDCP issues can also cause no-signal problems or weird wrong-resolution behavior.

Most testable facts: VGA is analog, HDMI and DisplayPort are digital, DVI variants differ, and digital-to-analog conversion usually needs an active adapter.

7. Storage and Internal Power Connectors: the plugs that matter when you’re working inside a desktop

SATA is the common storage interface for many HDDs, SSDs, and optical drives. It uses a narrow SATA data connector and a wider SATA power connector. They’re both part of the SATA family, but they do different jobs and you can’t swap them around. SATA revisions can affect speed, but the connector shape itself stays basically the same. A SATA SSD is still slower than NVMe or other PCIe-based storage, but it’s absolutely worth knowing for A+ hardware recognition and everyday support work.

When installing a SATA drive, connect SATA data from the motherboard to the drive, connect SATA power from the power supply, then verify detection in BIOS/UEFI. If the drive shows up in BIOS or UEFI but not in the operating system, the next place I’d check is Disk Management or whatever disk utility that OS uses, because it might just need to be initialized and formatted.

PATA, also called IDE, is a legacy ribbon-cable storage interface. Older PATA devices may require master/slave or cable-select jumper settings. Molex is a legacy 4-pin peripheral power connector, not a data connector. I’d be pretty cautious with cheap Molex-to-SATA power adapters, because the low-quality ones have a bad habit of causing reliability and safety problems.

Also recognize major internal power connectors: 24-pin ATX motherboard power, 4/8-pin CPU power, PCIe 6/8-pin GPU power, and SATA power. Damaged internal power connectors shouldn’t be forced or casually reused, because overheating and electrical risk are very real concerns.

Most testable facts: SATA data is narrow, SATA power is wider, PATA is ribbon-based legacy storage, Molex is legacy power, and BIOS or UEFI detection is an early troubleshooting step.

8. Structured Cabling: how building network wiring is usually organized

Structured cabling organizes building wiring into a predictable path: device → patch cable → wall jack → horizontal cabling → patch panel → switch. That model is essential for office troubleshooting. If a desk has no network, don't stop at the PC—trace the whole path.

Keystone jacks and patch panels commonly terminate Ethernet horizontal cabling using 110-style IDC punchdown terminations. 66 blocks are more associated with legacy voice systems, while 110 blocks are used for higher-density voice and data terminations. For day-to-day Ethernet support, patch panels and keystone jacks matter more than punchdown blocks as a general concept.

Termination should follow T568A or T568B consistently on both ends. A basic cable tester can spot opens, shorts, reversals, and some pair-mapping problems faults, but it won’t fully certify a run. Certification requires more advanced test equipment.

Labeling matters. Good documentation maps wall jack IDs to patch panel ports and switch ports. That cuts down downtime and also improves security by making unauthorized patching easier to notice.

For cable jacket ratings, know the basics: CMP is plenum-rated, CMR is riser-rated, and CM/CMG are general-purpose ratings. The required rating depends on local building and fire code, not just what's convenient.

9. Legacy Connectors Still Seen on the Exam

A+ still expects recognition of some older connectors even if you see them less often in modern offices. RJ-11 refers informally to telephone-style modular connectors. DB-9 is a common serial connector reference. DB-25 is associated with older parallel interfaces. PS/2 is the round keyboard or mouse connector used on older systems. eSATA is external SATA for older storage devices. You may also encounter FireWire/IEEE 1394 in legacy peripheral discussions. These are lower priority than USB, Ethernet, and HDMI, but still worth recognizing.

10. Troubleshooting Workflow, Tools, Security, and Safety

A solid cable workflow is: identify cable type → inspect connector and jacket → confirm port or device compatibility → swap known-good cable → test port or device → use tools if needed. That order solves a surprising number of tickets.

Useful tools include a cable tester for continuity and wire mapping, a toner probe for tracing cables, and interface-specific loopback plugs for port diagnostics. Loopback plugs are not universal cable testers; they are used for particular interfaces. For Ethernet, also check link lights, NIC status, negotiated speed, and whether the device obtains network connectivity after a cable swap.

Common physical faults include broken latches on Ethernet plugs, bent video pins, loose F-type coax fittings, crushed patch cords, dirty fiber ends, and partially seated SATA connectors. Intermittent symptoms when a cable is moved usually point to physical damage or poor strain relief.

Security and safety matter too. An unused live network jack can provide unauthorized access if port security is weak. Patch panels and telecom rooms should be controlled physically. Cable labels should help operations without exposing sensitive information unnecessarily. Never stare into fiber ports, and never force damaged internal power connectors inside a PC.

11. A+ Exam Focus and Rapid Review

High-yield exam traps: RJ-11 is not Ethernet, USB-C does not guarantee video or Thunderbolt, VGA is analog, DVI variants differ, Cat 6 does not guarantee 10 Gb to 100 m, and fiber type plus transceiver must match.

Best study method: do not memorize cables in isolation. Tie each one to a device and scenario. Desktop to switch means Ethernet. Cable modem means coax plus Ethernet. Building uplink means fiber. Printer likely means USB. Legacy projector may mean VGA and an active converter. Internal 2.5-inch SSD means SATA data plus SATA power.

If you can identify the connector, match it to the device, and spot the common compatibility mistake, you are thinking the way CompTIA wants you to think.