Applied Information Technology Engineer Examination cheat sheet

CPU performance: execution time = instruction count × CPI × clock cycle time; improving any one factor by k reduces time by k only if the others are unchanged.

Amdahl's law: speedup = 1 / ((1 - p) + p/s), where p is the parallelizable fraction and s the speedup of that fraction; bounds overall gain regardless of processor count.

Cache hierarchy: L1 hit ≈ 1–4 cycles, L2 ≈ 10–20, main memory ≈ 100–300; locality (temporal and spatial) determines hit rate, and average access time = hit time + miss rate × miss penalty.

OS scheduling: round-robin gives bounded wait but poor throughput for CPU-bound jobs; priority scheduling risks starvation, mitigated by aging; SJF minimizes average waiting time when burst times are known.

Relational model: primary key uniquely identifies a tuple; foreign key references another relation's primary key and enforces referential integrity; normalization to 3NF removes transitive dependencies on non-key attributes.

SQL: WHERE filters rows before grouping, HAVING filters groups after GROUP BY; NULL comparisons require IS NULL; COUNT(*) counts rows while COUNT(col) ignores NULLs.

TCP vs UDP: TCP provides connection setup (3-way handshake), ordered delivery, retransmission, and flow/congestion control; UDP is connectionless with no delivery guarantee, suited to real-time traffic.

Subnetting: usable hosts per subnet = 2^(32 - prefix) - 2; /24 yields 254 usable addresses; private ranges are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16.

Symmetric vs asymmetric crypto: AES is fast and used for bulk data; RSA/ECC solves key distribution but is slow; TLS combines them-asymmetric for key exchange, symmetric for the session.

Earned value: CV = EV - AC (negative = over budget); SV = EV - PV (negative = behind schedule); CPI = EV/AC; SPI = EV/PV; EAC ≈ BAC/CPI when current cost performance persists.

Critical path method: the critical path is the longest path through the dependency network; its length equals the minimum project duration, and any delay on it delays the project.

ITIL 4 incident vs problem: an incident is an unplanned interruption restored by incident management; a problem is the underlying cause investigated by problem management to prevent recurrence.

SLA design: availability percentage translates to downtime per year-99.9% ≈ 8.76 hours, 99.99% ≈ 52.6 minutes, 99.999% ≈ 5.26 minutes.

Risk response types: avoid, transfer (insurance/outsourcing), mitigate, accept for threats; exploit, share, enhance, accept for opportunities.

COBIT separates governance from management; governance evaluates, directs, and monitors, while management plans, builds, runs, and monitors activities.

RTO is the maximum tolerable downtime after a disaster; RPO is the maximum tolerable data loss measured in time. Backup frequency is driven by RPO, redundancy by RTO.

Service desk metrics: first-contact resolution rate, average handle time, and backlog age; a rising reopen rate signals inadequate root-cause fixes rather than agent speed issues.

Porter's five forces: rivalry, threat of new entrants, threat of substitutes, bargaining power of buyers, bargaining power of suppliers; high force intensity compresses industry profitability.

SWOT pairs internal strengths/weaknesses with external opportunities/threats; strategy formulation matches strengths to opportunities (SO) and defends against threats (ST).

Three generic strategies: cost leadership, differentiation, and focus (cost or differentiation within a niche); being stuck in the middle yields below-average returns.

BCG matrix: stars (high growth, high share) need investment; cash cows fund others; question marks require selective investment; dogs are candidates for divestment.

EA frameworks: Zachman is a taxonomy of artifacts (what, how, where, who, when, why); TOGAF's ADM is an iterative cycle from architecture vision through migration planning and change management.

IT investment appraisal: NPV discounts future cash flows at the cost of capital and accepts projects with NPV > 0; IRR is the discount rate making NPV zero; payback ignores cash flows after breakeven.

Business/IT alignment: the IT strategy must trace to business objectives; a portfolio map classifies investments as run-the-business, grow-the-business, or transform-the-business.

Outsourcing decision: core competencies stay in-house; commodity or scale-sensitive functions are candidates for outsourcing, with lock-in, exit cost, and knowledge loss as key risks.

Digital disruption: sustaining innovation improves existing products for current customers; disruptive innovation initially underperforms on mainstream metrics but wins on cost, access, or simplicity.

Copyright protects expression, not ideas or algorithms; software source code is protected as a literary work, and a clean-room reimplementation avoids copying protected expression.

Trade secrets require reasonable secrecy measures and have no fixed expiry; patents require novelty, inventive step, and industrial applicability, and last 20 years from filing.

Personal data protection: collect only the minimum necessary, specify the purpose, obtain consent where required, and honor access, correction, and deletion requests.

Information security triad: confidentiality (encryption, access control), integrity (hashing, checksums), availability (redundancy, DDoS protection); non-repudiation is provided by digital signatures.

Digital signature: sign with the sender's private key and verify with the sender's public key; it provides authenticity and integrity, not confidentiality-encrypt separately for secrecy.

Professional ethics: an engineer must not conceal known defects, must report conflicts of interest, and must decline work outside their competence rather than accept and improvise.

Contract types: fixed-price transfers cost risk to the vendor and suits stable requirements; time-and-material suits evolving scope; a penalty clause must be proportionate to be enforceable.

Standardization: de jure standards are ratified by bodies (ISO, IEC, IEEE); de facto standards arise from market dominance; conformance testing verifies interoperability claims.