Punjab PSEB SS Computer Application cheat sheet

Number systems: binary base 2, octal base 8, decimal base 10, hexadecimal base 16; each hex digit maps to exactly 4 binary bits.

1 byte = 8 bits; 1 KB = 1024 bytes; 1 MB = 1024 KB; 1 GB = 1024 MB; 1 TB = 1024 GB.

Two's complement: invert all bits of the magnitude and add 1; an n-bit signed range is -2^(n-1) to 2^(n-1) - 1.

Logic gates: AND outputs 1 only if all inputs are 1; OR outputs 1 if any input is 1; XOR outputs 1 only for an odd number of 1 inputs; NAND and NOR are universal gates.

De Morgan's laws: NOT(A AND B) = (NOT A) OR (NOT B); NOT(A OR B) = (NOT A) AND (NOT B).

OSI has 7 layers (Physical, Data Link, Network, Transport, Session, Presentation, Application); TCP/IP has 4 layers.

IPv4 addresses are 32-bit; IPv6 addresses are 128-bit; a Class C IPv4 network uses a /24 mask with 254 usable hosts.

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

CPU cycle: Fetch → Decode → Execute → Store; the ALU performs arithmetic and logic while the control unit sequences instructions.

AI is the simulation of human intelligence processes by machines; its core subfields are machine learning, natural language processing, computer vision, robotics and expert systems.

Machine learning types: supervised (labelled data), unsupervised (unlabelled data, clustering), and reinforcement learning (reward signal from an environment).

Classification predicts a discrete label; regression predicts a continuous numeric value; clustering groups unlabelled data by similarity.

Training set fits model parameters; validation set tunes hyperparameters; test set gives the final unbiased performance estimate.

Overfitting = low training error but high test error; remedies include more data, regularization, dropout and simpler models.

Confusion matrix terms: True Positive, True Negative, False Positive, False Negative; Accuracy = (TP + TN) / (TP + TN + FP + FN).

Precision = TP / (TP + FP); Recall = TP / (TP + FN); F1 = 2 × (Precision × Recall) / (Precision + Recall).

A perceptron computes a weighted sum of inputs plus a bias and passes it through an activation function such as ReLU, sigmoid or tanh.

Turing Test: a human judge converses with a machine and a human; the machine passes if the judge cannot reliably tell which is which.

Backpropagation applies the chain rule to compute gradients of the loss with respect to each weight; gradient descent updates w ← w − η·∂L/∂w, where η is the learning rate.

Convolution layers apply learnable filters with shared weights to detect local spatial features; pooling layers reduce spatial dimensions and parameter count.

Recurrent networks process sequences with a hidden state carried across time steps; LSTM and GRU gates mitigate the vanishing gradient problem.

Transformer self-attention computes Attention(Q, K, V) = softmax(QKᵀ/√d_k)·V, allowing parallel processing of whole sequences.

Large language models are autoregressive next-token predictors trained on large corpora; temperature controls sampling randomness and top-p/top-k truncate the candidate token set.

Tokenization splits text into subword units; context window is the maximum number of tokens a model can attend to at once.

Reinforcement learning notation: state s, action a, reward r, policy π(a|s), discount factor γ; Q-learning updates toward r + γ·max Q(s′, a′).

Ethical AI concerns include dataset bias, lack of explainability, privacy leakage, and accountability for automated decisions.

Model evaluation for imbalanced data should use precision, recall, F1 or AUC-ROC rather than raw accuracy alone.

Keyboard shortcuts: Ctrl+C copy, Ctrl+X cut, Ctrl+V paste, Ctrl+Z undo, Ctrl+Y redo, Ctrl+S save, Ctrl+P print, Ctrl+F find.

Spreadsheet cell references: relative (A1) changes on copy; absolute ($A$1) stays fixed; mixed ($A1 or A$1) fixes only one part.

Common spreadsheet functions: SUM(range), AVERAGE(range), COUNT, COUNTA, MAX, MIN, IF(condition, value_if_true, value_if_false), VLOOKUP.

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

HTML document skeleton: , , with , and <body> holding visible content.</p>

Common HTML tags:

paragraph, hyperlink, image,

/
with
1. lists, //

   tables.

File formats: .docx word processing, .xlsx spreadsheet, .pptx presentation, .pdf portable document, .jpg/.png images, .mp4 video, .zip compressed archive.

Cyber safety: phishing is a fraudulent message that tricks users into revealing credentials; strong passwords mix length and character types and are never reused.

E-governance and digital payment basics: UPI, net banking and digital wallets require OTP or PIN verification; never share OTP, CVV or PIN with anyone.