Resource Cheatsheet
A+ Core 1 3.2: Peripheral Cables
Professor Messer A+ 220-1201 objective 3.2 — USB versions and speeds, connector types and USB-C, DB-9 serial, RS-232 console access, and Thunderbolt 1 to 4.
- Updated
- Reading time
- 6 min read
- Detail
- A+ Core 1
- Detail
- Peripheral Cables
On this page
In one line: USB speeds climb from 1.5 Mbps to 20 Gbps across versions 1.1 to 3.2, USB-C is one reversible connector that says nothing about the signal on it, DB-9 serial survives for console access when nothing else works, and Thunderbolt carries 40 Gbps plus power on a daisy-chainable USB-C cable.
Companion to: Professor Messer, CompTIA A+ 220-1201 Core 1, objective 3.2 (Peripheral Cables). The full version is the Peripheral Cables class notes; the section overview is the Section 3 sheet.
USB speeds
| Version | Name | Max speed | Approx. cable |
|---|---|---|---|
| 1.1 | Low speed | 1.5 Mbps | 3 m |
| 1.1 | Full speed | 12 Mbps | 5 m |
| 2.0 | High speed | 480 Mbps | 5 m |
| 3.0 | SuperSpeed | 5 Gbps | 3 m |
| 3.1 | — | 10 Gbps | — |
| 3.2 | — | 20 Gbps | — |
Lengths are approximate — the USB spec sets no exact maximum; these are the practical limits for that throughput. Extend with a powered hub, not a longer passive cable.
Beyond the exam: 3.0 is now marketed as 3.2 Gen 1, 3.1 as 3.2 Gen 2, 20 Gbps as 3.2 Gen 2x2; USB4 = 40 Gbps, built on Thunderbolt 3.
USB connectors
| Connector | USB 1.1 / 2.0 | USB 3.0 |
|---|---|---|
| Standard-A | Familiar rectangular plug | Same form factor |
| Standard-B | Squarer — printers, peripherals | Slightly taller |
| Mini-B | Small, mobile devices | — |
| Micro-B | Smaller still | Completely different shape |
A 2.0 Micro-B cable fits part of a 3.0 Micro-B socket and works — at 2.0 speeds. Looks like a slow drive, is actually the wrong cable.
USB-C
| Point | Detail |
|---|---|
| What | One connector replacing all the earlier types |
| Reversible | No correct orientation — plug it in either way |
| Critical | It describes the physical interface only, not the signal — USB data, DisplayPort, Thunderbolt or power can all run over it |
| Size | Similar to Micro-B; much smaller than Standard-A |
Two identical-looking USB-C cables can differ wildly: 40 Gbps + 100 W versus charge-only. The cable is always a prime suspect when a USB-C dock or monitor misbehaves.
Serial and console
| Term | Detail |
|---|---|
| Connectors | DB-25 (25 pins, B-size shell) · DB-9 (9 pins, properly DE-9 — E-size shell, but the DB name stuck) |
| Signalling | RS-232 (Recommended Standard 232) — predates USB, mice and keyboards |
| Today | Legacy switches, routers, firewalls — the console port |
| Why it matters | Works when no other method does — it doesn’t depend on the network. Drops you at a command prompt |
| Console interface | Note |
|---|---|
| RJ45 | Looks like Ethernet, carries serial — the classic trap |
| DB-9 | Traditional serial connector |
| USB | Common on newer switches and routers |
Adapter chain from a modern laptop: USB/USB-C → USB-to-serial adapter (enumerates as a COM port) → DB-9 → DB-9-to-RJ45 console cable → CONSOLE port. Terminal defaults are usually 9600 8N1.
Thunderbolt
| Version | Connector | Throughput | Notes |
|---|---|---|---|
| TB1 | Mini DisplayPort | 10 Gbps × 2 channels = 20 Gbps | Reused an existing connector |
| TB2 | Mini DisplayPort | 20 Gbps aggregated | Channels combined |
| TB3 | USB-C | 40 Gbps | 3 m copper · up to 60 m optical |
| TB4 | USB-C | 40 Gbps | Dual-4K video, more PCIe bandwidth |
- Data and power on one cable — a peripheral runs from a single connection.
- Daisy chaining: laptop → monitor → monitor → storage. Thunderbolt tracks which device is which; no need for a port each.
- TB3 could often drive dual 4K already; TB4 makes it a required minimum (plus ≥32 Gbps PCIe). TB4’s story is consistency, not raw speed.
- A Thunderbolt port is USB-C shaped — same shape, different capability.
🔐 Security notes
- USB is the classic physical attack surface: a device can present as a keyboard and type commands on insertion. Port control policy, disable unused ports, never plug in found devices.
- Thunderbolt exposes PCI Express directly — that’s the speed, and it means a malicious device may reach memory over DMA. IOMMU plus device approval prompts mitigate it; never set “always allow”, never plug in unknown docks.
- Console ports are unauthenticated physical access by design — the cabinet lock is the access control. Network gear belongs in locked rooms.
- A USB-C plug says nothing about what the cable does — treat public charging cables and borrowed docks as untrusted; use a charge-only cable or your own adapter.
- Daisy chains extend trust — everything downstream shares the same high-speed path.
- Adapters are devices too, and a technician’s USB-to-serial adapter touches every switch in the estate. Known sources only.
Practice drills
1. USB 1.1, 2.0, 3.0, 3.1, 3.2 speeds?
1.5/12 Mbps · 480 Mbps · 5 Gbps · 10 Gbps · 20 Gbps. 3.0 is branded SuperSpeed.
2. Why are USB cable lengths "approximate"?
The specification sets no exact maximum — the figures are the practical limits for maintaining that throughput.
3. Which USB 3.0 connector changed shape completely?
Micro-B. Standard-A kept its form factor; Standard-B just got taller.
4. What does a USB-C connector tell you about the signal?
Nothing. It’s a physical interface only — USB, DisplayPort, Thunderbolt or power can all run over it.
5. Why is DB-9 really DE-9?
The letter is the shell size in the D-subminiature family. Nine pins use the E shell; the “DB” name carried over from the 25-pin DB-25.
6. Why does console access still matter?
It works when nothing else does — it doesn’t depend on the network. You get a command prompt on a switch, router or firewall.
7. What's the trap with an RJ45 console port?
It looks like Ethernet but carries serial signalling. A normal patch lead accomplishes nothing.
8. Thunderbolt 3: connector, speed, distances?
USB-C, 40 Gbps, 3 m copper or up to 60 m optical. Supports daisy chaining, and carries power on the same cable.
Key takeaways
- USB: 1.5/12 Mbps → 480 Mbps → 5 → 10 → 20 Gbps; lengths approximate, ~3–5 m.
- Connectors: Standard-A/B, Mini-B, Micro-B — 3.0’s Micro-B is a different shape entirely.
- USB-C = one reversible connector, and it says nothing about the signal carried.
- DB-9 (DE-9) / RS-232 lives on as console access — RJ45 console ports are serial, not Ethernet.
- Thunderbolt: data + power, daisy chains, Mini DisplayPort on TB1/2 and USB-C at 40 Gbps on TB3/4.