CTSF cheat sheet

Bit = one binary digit (0 or 1); byte = 8 bits; 1 KB = 1024 bytes in binary convention, 1000 bytes in decimal (SI) convention.

Storage scaling: 1 MB = 1024 KB, 1 GB = 1024 MB, 1 TB = 1024 GB; vendor drive capacities often use decimal units, so an advertised 1 TB drive shows ~931 GB in binary-based OS displays.

Throughput vs. latency: throughput is data volume per unit time (MB/s, Gbps); latency is delay per operation (ms). Raising bandwidth does not reduce latency.

Bandwidth unit conversion: 1 Gbps = 1000 Mbps; divide Mbps by 8 to approximate MB/s (100 Mbps ≈ 12.5 MB/s theoretical).

Virtualization: a hypervisor (Type 1 bare-metal, Type 2 hosted) multiplexes physical CPU, RAM, storage, and NIC resources among guest VMs.

Cloud service models: IaaS supplies compute/storage/network; PaaS adds runtime and middleware; SaaS delivers the finished application.

API = defined contract for software-to-software calls; REST uses HTTP verbs (GET read, POST create, PUT/PATCH update, DELETE remove) and status codes (2xx success, 4xx client error, 5xx server error).

Common file extensions map to content type: .exe/.msi executables/installers, .pdf portable document, .csv plain-text delimited data, .iso optical image, .log text event records.

RAM is volatile working memory; DRAM (DIMM/SO-DIMM) loses contents on power loss, while NAND flash (SSD) and magnetic disks (HDD) are non-volatile.

Storage media trade-off: HDD = high capacity per dollar, mechanical latency; SSD = low latency and shock resistance, higher cost per GB, finite write endurance (TBW).

Connector reference: USB-A/USB-C, HDMI, DisplayPort, RJ-45 (Ethernet), 3.5 mm audio, SATA (internal drives), M.2 (NVMe SSD slot), Thunderbolt (USB-C form factor).

Peripheral classes: input (keyboard, scanner, webcam), output (monitor, printer, speaker), and both (touchscreen, multifunction printer).

Printer consumables differ by technology: laser uses toner cartridges and imaging drums; inkjet uses ink cartridges; thermal uses coated paper with no ink.

POST (power-on self-test) runs at boot; repeated beep codes or a blank display point to RAM, GPU, or power supply faults before the OS loads.

PSU ratings: wattage must cover peak component draw; 80 PLUS efficiency ratings (Bronze to Titanium) indicate conversion efficiency, not output capacity.

Hot-swappable components (e.g., SAS/SATA drive bays, redundant PSUs on servers) can be replaced while powered; CPU and RAM are not hot-swappable on typical systems.

IPv4 address = 32 bits in four dotted octets; private ranges are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16; 127.0.0.1 is loopback.

Subnet mask /24 = 255.255.255.0 and yields 254 usable host addresses (256 minus network and broadcast).

IPv6 is 128 bits written as eight hexadecimal groups; link-local addresses begin fe80:: and are not routed.

DHCP leases IP address, subnet mask, default gateway, and DNS servers automatically; APIPA (169.254.x.x) means the DHCP request failed.

DNS resolves names to IP addresses; record types include A (IPv4), AAAA (IPv6), CNAME (alias), MX (mail), and PTR (reverse lookup).

Ports to know: 22 SSH, 25 SMTP, 53 DNS, 80 HTTP, 443 HTTPS, 3389 RDP; TCP is connection-oriented and reliable, UDP is connectionless and unacknowledged.

Wi-Fi standards by band: 802.11n (2.4/5 GHz), 802.11ac (5 GHz), 802.11ax/Wi-Fi 6 (2.4/5/6 GHz); 2.4 GHz reaches farther but is more congested than 5 GHz.

Troubleshooting order for connectivity: physical link (cable/link LED) → IP configuration (ipconfig/ifconfig) → gateway ping → DNS resolution → application port test.

Windows file systems: NTFS supports permissions, quotas, and journaling; FAT32 caps a single file at 4 GB; exFAT is used for large removable media.

Linux permission notation rwx = 4+2+1; chmod 755 grants owner read/write/execute and group/others read/execute.

Windows paths: %SystemRoot% is typically C:\Windows, %TEMP% is the per-user temp folder, and C:\Users<name>\AppData holds per-user application data.

Least-privilege execution: standard user accounts for daily work; administrative elevation (UAC on Windows, sudo on Linux) only for specific tasks.

Software lifecycle: install (MSI/EXE, apt, yum/dnf, package managers) → update/patch → uninstall; patches close known vulnerabilities and should be tracked by version.

32-bit vs. 64-bit: 32-bit processes address ~4 GB of memory; 64-bit OS and applications are required to use more RAM per process.

Backup types: full copies all selected data; incremental copies changes since the last backup of any type; differential copies changes since the last full backup.

Driver = OS-level software that translates commands for a specific hardware device; a mismatched driver commonly causes device errors or stop errors.

CIA triad: confidentiality (only authorized read access), integrity (data unaltered and trustworthy), availability (systems reachable when needed).

Authentication factors: something you know (password/PIN), something you have (token, phone), something you are (biometrics); MFA requires two or more different factor types.

Encryption at rest protects stored data (BitLocker, LUKS, file/folder encryption); encryption in transit protects data on the wire (TLS/HTTPS, VPN).

Phishing indicators: mismatched sender domain, urgency, unexpected attachments, hover-link destination differing from displayed text; report rather than click.

Malware categories: virus (attaches to files), worm (self-propagates over networks), trojan (disguised as legitimate), ransomware (encrypts and demands payment), spyware (collects activity).

Password storage best practice: salted one-way hashes (e.g., bcrypt/Argon2), never plaintext or reversible encryption; length and uniqueness matter more than forced complexity churn.

Least privilege and need-to-know govern data access; role-based access control (RBAC) assigns permissions to roles rather than individuals.

Privacy principles: collect only necessary personal data (minimization), state purpose, limit retention, and honor subject access/deletion requests per applicable policy and law.

Incident priority = impact × urgency; a high-impact, high-urgency outage outranks a low-impact single-user request regardless of ticket age.

Ticket lifecycle: new → assigned → in progress → resolved → closed; reopening a closed ticket is a new record of the same issue.

SLA vs. OLA: an SLA is a customer-facing commitment (response and resolution targets); an OLA is an internal agreement between teams supporting the SLA.

Escalation types: functional (to a more skilled technician) and hierarchical (to management for authority or resources).

Troubleshooting method: identify the problem → establish a theory → test the theory → plan/implement the fix → verify full functionality → document findings.

Change management: request → review/approve → schedule → implement → verify → rollback plan documented before any change is applied.

First-line data gathering: exact error text, when it started, what changed recently, scope (one user vs. many), and reproducible steps.

Knowledge base articles should record symptom, cause, resolution steps, and affected versions so recurring issues resolve faster and consistently.

Confidentiality: do not disclose client data, credentials, or incident details to unauthorized parties; share only on a need-to-know basis.

Professional ethics: avoid conflicts of interest, do not accept gifts that could influence decisions, and disclose any relationship that could bias support.

Communication structure: acknowledge the issue, state what you will do and when, give realistic timelines, and confirm the user understands before closing.

Plain-language rule: replace jargon with user-level terms (say "restart the computer," not "reinitialize the host") unless the audience is technical.

Active listening: let the user finish, paraphrase the problem back, and ask clarifying questions rather than interrupting with a solution.

Handling an upset user: stay calm and factual, avoid blame, focus on the fix, and escalate when the request exceeds your authority.

Documentation discipline: record actions, timestamps, and outcomes in the ticket so others can continue the work without re-interviewing the user.

Data handling ethics: access only records required for the task, and follow policy for retention, disposal, and reporting suspected breaches promptly.