220-1201 cheat sheet: CompTIA A+ Core 1

Mobile devices

Laptop displays: OLED (per-pixel lighting, true black) vs. IPS LCD (backlit, wider viewing angle, cheaper). Digitizer is the touch-input layer, separate from the display panel underneath it.
Mobile connectivity: Bluetooth pairing, NFC (tap-to-pay, very short range), GPS, cellular radio bands. Airplane mode disables all of them at once.
Common laptop repairs are largely component-swap (RAM, SSD, battery, keyboard) rather than board-level; know which components are field-replaceable vs. which require a manufacturer service centre.
Mobile device accessories and ports: USB-C is now the common charge/data port across most modern phones and tablets; know Lightning as the older Apple-specific alternative.

IPv4 addressing: classes, private ranges (10.x, 172.16–31.x, 192.168.x), subnet masks, CIDR notation. IPv6 uses 128-bit addresses in hextet (colon-separated) notation.
Common ports to know by number and protocol: 80/443 (HTTP/HTTPS), 21/22 (FTP/SSH), 25 (SMTP), 53 (DNS), 3389 (RDP).
Networking hardware: switch (Layer 2, forwards by MAC), router (Layer 3, forwards by IP), access point (wireless bridge to the wired LAN), firewall (filters traffic by rule).
Wireless standards (802.11 a/b/g/n/ac/ax) and their rough frequency bands (2.4 GHz vs. 5 GHz vs. 6 GHz) — know that higher-numbered standards generally mean faster and/or more efficient, not a strict ladder of range.

CPU sockets must match the motherboard; core count, cache, and clock speed all affect performance differently — more cores helps multitasking, higher clock helps single-thread speed.
RAM: match speed/type to what the motherboard supports (DDR4 vs. DDR5 are not interchangeable); dual/quad-channel needs matched pairs installed in the correct slots.
Storage: SSD (NAND flash, no moving parts, fast) vs. HDD (spinning platters, slower, cheaper per GB) vs. NVMe (SSD over the faster PCIe bus rather than SATA).
Power supplies: match wattage to the system's actual draw with headroom; 80 PLUS ratings (Bronze/Silver/Gold/Platinum/Titanium) indicate efficiency, not raw output.

A hypervisor runs virtual machines: Type 1 (bare metal, runs directly on hardware — used in datacentres) vs. Type 2 (runs as an application on top of a host OS — used on a technician's own laptop).
VM resource requirements: allocate CPU, RAM, and storage from the host; over-allocating across many VMs can starve them all.
Cloud service models: IaaS (raw infrastructure), PaaS (a managed platform to deploy on), SaaS (a finished application) — know which layer a technician is actually responsible for in each.
Common cloud characteristics: on-demand self-service, rapid elasticity, resource pooling, measured (metered) usage.

The six-step troubleshooting methodology: identify the problem → establish a theory of probable cause → test the theory → establish a plan and implement the solution → verify full system functionality → document findings.
Common hardware symptoms and likely causes: no POST (power, RAM seating, or display cable), overheating/shutdown (dust, failed fan, dried thermal paste), intermittent connectivity (a failing cable or NIC).
Network troubleshooting order: check physical layer first (cable, link light) before chasing a software or configuration explanation.
Always document the fix and the root cause — not just that the ticket was closed — for the next technician who sees the same symptom.

Reading a summary is the easy part. Take the free 10-question diagnostic to see which of these domains you actually have, then drill the rest.