JCE Computer Studies cheat sheet

Von Neumann architecture: CPU (ALU + control unit + registers), memory, I/O; instructions and data share the same memory bus.

Fetch–decode–execute cycle: PC holds next instruction address; MAR/MDR mediate memory transfers; IR holds the fetched instruction.

CPU performance: execution time = instruction count × CPI × clock cycle time; clock rate = 1 / cycle time.

Cache hierarchy: L1 fastest/smallest, then L2, L3, then RAM; hit ratio = hits / total accesses; locality (temporal and spatial) drives hit rates.

RISC vs CISC: RISC uses fixed-length instructions and load/store architecture; CISC allows variable-length, memory-operand instructions.

Primary storage is volatile (RAM, ROM is non-volatile but read-mostly); secondary storage (HDD, SSD, optical) is non-volatile.

Buses: address bus width determines addressable memory (2^n locations); data bus width determines words transferred per cycle.

Input devices convert physical signals to digital data; output devices convert digital data to human-perceivable form; both connect via controllers and ports.

System software (OS, utilities, drivers) manages hardware; application software performs user tasks.

OS functions: process management, memory management, file systems, device I/O, security, and user interface.

Process states: new → ready → running → waiting → terminated; the scheduler moves processes between ready and running.

Multiprogramming keeps several jobs in memory; multitasking time-slices the CPU; multiprocessing uses multiple CPUs.

Virtual memory maps logical addresses to physical frames via page tables; a page fault triggers loading from secondary storage.

Deadlock requires mutual exclusion, hold-and-wait, no preemption, and circular wait; breaking any one condition prevents it.

File systems organize data into directories and files; FAT, NTFS, and ext4 differ in metadata, journaling, and permission models.

Utility software includes antivirus, backup, disk defragmenter, and compression tools; device drivers translate OS calls to hardware commands.

Positional notation: value = Σ digit_i × base^i; base 2 (binary), 8 (octal), 10 (decimal), 16 (hexadecimal).

Binary to hex: group bits in fours from the right; binary to octal: group in threes.

Unsigned n-bit range: 0 to 2^n − 1; signed two's complement range: −2^(n−1) to 2^(n−1) − 1.

Two's complement: invert all bits and add 1 to negate; subtraction A − B = A + (−B) in two's complement.

Character encoding: ASCII uses 7 bits (128 codes); extended ASCII 8 bits; Unicode assigns code points (e.g., U+0041 = 'A').

Data units: 1 byte = 8 bits; 1 KB = 1024 bytes (binary convention); 1 MB = 1024 KB; 1 GB = 1024 MB.

Floating point (IEEE 754): sign, exponent, mantissa; normalized form 1.m × 2^e; precision limited by mantissa bits.

Overflow occurs when a result exceeds the representable range; underflow when a floating-point value is too small to represent.

OSI layers: Physical, Data Link, Network, Transport, Session, Presentation, Application; TCP/IP model merges Session/Presentation into Application.

LAN vs WAN: LAN covers a limited area with high speed; WAN spans large distances, often using leased lines or packet switching.

IP addresses: IPv4 is 32 bits (dotted decimal); IPv6 is 128 bits (hex colon-separated); subnet mask separates network and host portions.

TCP is connection-oriented and reliable (three-way handshake, ACKs, retransmission); UDP is connectionless and best-effort.

DNS resolves domain names to IP addresses; HTTP/HTTPS (port 80/443) transfer web content; SMTP (25) sends email; POP3/IMAP retrieve it.

Topologies: star (central switch), bus (shared backbone), ring (token passing), mesh (redundant links); star is most common in LANs.

Transmission media: twisted pair (Cat5e/Cat6), coaxial, fiber optic (high bandwidth, immune to EMI), and wireless (Wi-Fi, cellular).

Bandwidth is capacity (bps); latency is delay; throughput is actual delivered rate; packet switching shares links statistically.

DBMS functions: data definition, storage, retrieval, concurrency control, backup/recovery, and security enforcement.

Relational model: tables (relations) with rows (tuples) and columns (attributes); primary key uniquely identifies rows; foreign key references another table's primary key.

Normalization: 1NF removes repeating groups; 2NF removes partial dependencies; 3NF removes transitive dependencies.

SQL categories: DDL (CREATE, ALTER, DROP), DML (SELECT, INSERT, UPDATE, DELETE), DCL (GRANT, REVOKE).

ACID properties: Atomicity, Consistency, Isolation, Durability - guarantee reliable transaction processing.

Entity–relationship modeling: entities, attributes, relationships (1:1, 1:N, M:N); M:N requires a junction table in the relational model.

Information systems: TPS (transaction processing), MIS (management reporting), DSS (decision support), EIS (executive information).

Data validation checks: range, type, format, presence, and consistency; validation differs from verification (double entry, parity).

Algorithm properties: finite, definite, effective, and produces output from input; pseudocode and flowcharts express logic before coding.

Control structures: sequence, selection (IF/CASE), iteration (FOR, WHILE, REPEAT); a loop must have a terminating condition.

Sorting: bubble/insertion/selection are O(n²); merge/quick sort average O(n log n); binary search is O(log n) on sorted data.

Searching: linear search O(n) works on unsorted data; binary search requires sorted data and halves the search space each step.

Recursion: a function calls itself with a smaller input and a base case; each call uses stack space, risking stack overflow.

Variable scope: local variables exist within a procedure; global variables are accessible throughout; parameter passing can be by value or by reference.

Debugging: syntax errors violate language rules; logic errors produce wrong output; runtime errors occur during execution (e.g., division by zero).

Program testing: dry run traces values manually; test data includes normal, boundary, and invalid cases.

Word processing: styles apply consistent formatting; mail merge combines a main document with a data source; headers/footers repeat on pages.

Spreadsheets: cell references can be relative (A1), absolute ($A$1), or mixed; formulas begin with =; functions include SUM, AVERAGE, IF, VLOOKUP.

Spreadsheet charts: column/bar compare categories; line shows trends over time; pie shows parts of a whole.

Database packages: tables store records; queries filter and sort; forms simplify data entry; reports present formatted output.

Presentation software: slide masters enforce consistent design; transitions apply between slides; animations apply within slides.

Graphics: raster images are pixel grids (resolution-dependent); vector images use paths and shapes (scalable without loss).

File formats: .docx (word processing), .xlsx (spreadsheet), .pptx (presentation), .pdf (portable fixed layout), .csv (plain text tabular data).

Cloud productivity suites enable real-time collaboration, version history, and cross-device access, but depend on network availability.

Ethical principles: respect for privacy, intellectual property, accuracy, and responsible use of resources.

Malware types: virus (attaches to files), worm (self-replicates across networks), trojan (disguised as legitimate), ransomware (encrypts data for payment).

Security goals (CIA triad): confidentiality, integrity, availability; threats include interception, modification, and denial of service.

Authentication factors: something you know (password), have (token/phone), are (biometrics); two-factor authentication combines two types.

Encryption: symmetric uses one shared key (fast); asymmetric uses public/private key pairs (key exchange, digital signatures).

Safe practices: strong unique passwords, regular backups, software updates, firewalls, and caution with unsolicited links/attachments.

Computer safety: ergonomics (posture, screen height, breaks), electrical safety, and safe disposal of e-waste.

Legal frameworks: data protection laws govern personal data; copyright protects software; licenses define permitted use (proprietary, open source).

Artificial intelligence: machine learning builds models from data; supervised learning uses labeled examples; unsupervised learning finds patterns in unlabeled data.

Cloud computing service models: IaaS (infrastructure), PaaS (platform), SaaS (software); deployment models: public, private, hybrid.

Internet of Things (IoT): networked sensors and devices exchange data; challenges include security, privacy, and interoperability.

Big data characteristics: volume, velocity, variety, veracity, value; analytics extracts insight from large datasets.

Blockchain: distributed ledger with cryptographic linking of blocks; tamper-evident but energy-intensive for proof-of-work.

Automation and robotics affect employment: job displacement in routine tasks, creation of new roles, and need for reskilling.

Digital divide: unequal access to technology and connectivity, influenced by income, geography, and education.

Social media impacts: rapid information sharing and connectivity, but also misinformation, echo chambers, and privacy concerns.