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CompTIA A+ Core 1 (220-1201) Cheat Sheet

Fuad Efendi March 29, 2026 6 min read

Use a high-yield A+ Core 1 review sheet for ports, Wi-Fi, storage, printers, mobile basics, and support-side troubleshooting logic.

On this page

Use this for last-mile review. Core 1 rewards technicians who stay calm, verify the physical and compatibility basics first, and then choose the right tool, component, or settings path. If a line here feels too compressed, go back to the full lesson page before you keep drilling.

APIPA: Automatic private address in the 169.254.0.0/16 range that usually signals a DHCP failure path.

Final 20-minute recall (exam day)

    flowchart LR
	  A["Read the symptom"] --> B["Choose the fault lane"]
	  B --> C["Hardware, network, printer, or mobile"]
	  C --> D["Pick the least intrusive next step"]

What to notice:

  • Core 1 answers get easier when you classify the symptom first
  • the exam often rewards the safest useful next move, not the biggest fix

Cue -> best move (scenario map)

If the question says… Usually best answer
169.254.x.x address DHCP failure path: scope, relay, VLAN, server reachability
Names fail but IP works DNS issue (ipconfig /all, nslookup)
Printer smudges/ghosting Fuser/imaging path issue (laser maintenance parts)
Smartphone battery drains fast Background apps, radios, brightness, health/age check
New NVMe not detected Check M.2 keying/lane support, BIOS/UEFI mode, reseat
Slow Wi-Fi in crowded area 5 GHz or 6 GHz, channel planning, WPA2/3, disable WPS
Intermittent network drops Duplex/speed mismatch, bad cable/connector, duplicate IP
“Best redundancy + performance” storage RAID 10
Need secure remote admin SSH (not Telnet/RDP exposed broadly)
Multiple symptoms after one change Roll back and apply one-change-at-a-time method
One cable for desk setup Compatible dock or supported USB-C workflow

Must-memorize Core 1 anchors

Topic Fast recall
Private IPv4 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16
APIPA 169.254.0.0/16 (local-only, DHCP miss)
Port pairs DNS 53, DHCP 67/68, RDP 3389, SSH 22, HTTPS 443
Wi-Fi security order WPA3 -> WPA2 (AES/CCMP) -> WPA (TKIP) -> WEP
RAID shorthand 0 speed, 1 mirror, 5 parity, 10 mirror+stripe
Printer process Processing -> Charging -> Exposing -> Developing -> Transferring -> Fusing -> Cleaning

High-confusion pairs

Pair Fast distinction
M.2 vs NVMe form factor vs protocol
no power vs no boot electrical start vs startup path
ghosting vs jamming image-quality path vs feed-path issue
USB-C vs Thunderbolt connector shape vs higher-end supported feature set
hotspot vs tethering shared mobile data path, often Wi-Fi versus broader connection-sharing language

Last-minute traps

  • Choosing a disruptive fix before basic physical checks (power, cable, link, settings).
  • Treating snapshots as backups.
  • Leaving WPS/default credentials enabled on SOHO devices.
  • Mixing connector standards (M.2 SATA vs NVMe PCIe assumptions).
  • Confusing form factor, connector, and protocol as if they were the same decision.

1) Ports & Protocols (memorize)

Service Port/Proto Notes
HTTP / HTTPS 80 TCP / 443 TCP Web; HTTPS uses TLS
SSH 22 TCP Secure shell / SFTP
FTP / FTPS / SFTP 20–21 TCP / 990 TCP / 22 TCP Legacy vs TLS vs SSH
SMTP / Submission 25 / 587 TCP Outbound email
POP3 / IMAP4 (+TLS) 110 / 143 (995 / 993) TCP Mail retrieval
RDP 3389 TCP/UDP Remote desktop
DNS 53 UDP/TCP Name resolution
DHCP 67/68 UDP Server/client
SNMP 161/162 UDP Monitor / traps
LDAP / LDAPS 389 / 636 TCP Directory

2) Ethernet Cabling & Standards

Std Speed Max Dist Cable
100BASE-TX 100 Mbps 100 m Cat5/5e
1000BASE-T 1 Gbps 100 m Cat5e/6
10GBASE-T 10 Gbps 55 m (Cat6) / 100 m (Cat6a) Cat6/6a

3) Fiber & Transceivers

Type Mode Connector Range
MMF Multi-mode LC/SC Short (LED/VCSEL)
SMF Single-mode LC/SC Long (laser)

Notes: SFP/SFP+ modules match fiber type; clean ends; avoid tight bends.

4) Peripheral & Storage Connectors

  • USB: 2.0 (480 Mbps), 3.2 Gen1 (5 Gbps), Gen2 (10), Gen2x2 (20). USB-C supports alt-modes (DP/Thunderbolt).
  • Display: HDMI • DisplayPort (DP++) • DVI-D/I • VGA (legacy).
  • Storage: SATA (data 7-pin, power 15-pin), M.2 keys (B/M), NVMe over PCIe.
  • Thunderbolt 3/4: USB-C, up to 40 Gbps.

5) Wi-Fi Standards

Std Bands Max PHY (theoretical) Notes
802.11n (Wi-Fi 4) 2.4/5 ~600 Mbps MIMO
802.11ac (Wi-Fi 5) 5 ~6.9 Gbps MU-MIMO, wide channels
802.11ax (Wi-Fi 6/6E) 2.4/5/(6E) >9 Gbps OFDMA, dense env.

6) Wi-Fi Security & SOHO Hygiene

  • Security order (best→worst): WPA3 → WPA2 (AES/CCMP) → WPA (TKIP) → WEP (avoid).
  • SOHO basics: change defaults, WPA2/3-Personal, strong passphrase, firmware updates, disable WPS.

7) IPv4, DHCP & DNS Essentials

  • Private ranges: 10.0.0.0/8 • 172.16.0.0–172.31.255.255 (/12) • 192.168.0.0/16
  • APIPA: 169.254.0.0/16 → DHCP failure (local-only).
  • Quick tells: Names fail but IP works → DNS issue; duplicate IP → intermittent drops.

8) Network Triage (first moves)

  • APIPA: Check DHCP scope/reachability/relay, VLAN, gateway/DNS.
  • No network: Verify link light, NIC enablement, cabling/port.
  • Wi-Fi slow: Prefer 5/6 GHz, right channel width, reduce interference; disable WPS.

9) RAID Levels

RAID Disks Benefit Notes
0 2+ Performance No redundancy
1 2 Redundancy 50% capacity
5 3+ Redundancy + perf 1 disk fault tolerant
10 4+ Redundancy + perf Mirrored stripes

10) Filesystems & Storage Health

  • FS: NTFS (permissions, quotas, EFS), exFAT (flash), FAT32 (legacy).
  • SMART warnings: Back up, replace drive.
  • M.2/NVMe: Seat fully; confirm BIOS/UEFI detection; check boot order.

11) Printers — Laser Process & Fixes

Order: Processing → Charging → Exposing → Developing → Transferring → Fusing → Cleaning

Symptom Likely Cause First Step
Streaks/lines Drum/toner/fuser residue Clean/replace unit
Ghosting Drum/fuser not discharging Replace drum/fuser
Jams Rollers/path/humidity Clear path; clean rollers
Faint/uneven Low toner/transfer Replace toner; check transfer roller

12) Displays & Graphics

Symptom Cause Quick Action
No signal Loose cable / GPU not seated Reseat cables/GPU; check input
Artifacts/tearing Driver or cable Update driver; swap cable/port
Dim image Backlight/power Adjust brightness; test external
Color shift Profile/cable Reset profile; try HDMI/DP

13) Mobile Devices

  • Connectivity: Tethering vs hotspot; Wi-Fi calling.
  • Accessories: NFC, Bluetooth profiles (A2DP/HFP).
  • Triage: Safe mode (Android), DFU/Recovery (iOS), clear app cache/data, battery health.

14) Virtualization & Client Cloud

  • Type 1 vs Type 2 hypervisors (bare-metal vs hosted).
  • VM resources: vCPU, memory ballooning, vNICs.
  • Snapshots ≠ backups (short-term only).
  • Cloud use: Storage sync (OneDrive/Drive), thin clients, basic VDI awareness.

15) Windows CLI & Tools

Need Tool/Command Use
IP stack ipconfig /all DHCP/DNS/gateway check
Reachability ping, tracert Latency, path issues
Name resolution nslookup DNS testing
Shares net use Map drives; creds
Disk chkdsk, diskpart, defrag Filesystem/partition
System health sfc /scannow, DISM /Online /Cleanup-Image /RestoreHealth Image repair
Logs Event Viewer System/Application issues

16) ESD/Safety & Troubleshooting Method

ESD & safety: Strap to ground, antistatic mat, handle by edges, ESD bags; surge/UPS; toner cleanup with cold water/ESD-safe vac.

Method (always show this logic):

  1. Identify the problem (gather, duplicate, what changed).
  2. Establish a probable cause (theory).
  3. Test the theory → confirm root cause.
  4. Plan and implement the fix.
  5. Verify full functionality; implement prevention.
  6. Document findings/actions/outcomes.

Golden rules: Start least intrusive, change one thing at a time, preserve data and user impact awareness.

Where to go next

Use the study plan if you need pacing, the glossary if terms are blurring together, and the resources page when you want the current official CompTIA source links.

Quiz

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From here, go to the FAQ for deeper scenario explanations or use the resources page for official exam details and safe lab references.

5. Troubleshooting
Glossary