Notes, summaries, assignments, exams, and problems for Computers

Javascript Continued

Proximity

Proximity is all about using visual spaces to show relationships in your content. We can group the items in blocks of text or elements in the graphic to take visual emphasis.

White Space

White space, also known as negative space, refers to the spaces between your content, between lines, and even the margins. White space defines and separates different sections.

Alignment

We can separate text boxes, images, etc. by imagining their content as a range inside of a grid. Centering the images to the text and using equal size margins can create a visually pleasing alignment.

Contrast

Contrast means that one item is different from another. We can create contrast using color, size, shape, or contrasting styles of text. Hierarchy, a visual technique... Continue reading "Using Proximity, White Space, Alignment, Contrast, and Repetition in Design" »

Key Network Concepts and Design Principles

Essential Network Terminology

Usability

The ease with which network users can access the network and its services. This includes goals for simplifying user tasks.

Management (Fault, Configuration, Accounting, Performance, Security)

The five key areas of network management: Fault Management, Configuration Management, Accounting Management, Performance Management, and Security Management.

Bandwidth

The data-carrying capacity of a circuit, measured in bits per second (bits/sec).

Throughput

The quantity of error-free data transmitted per unit of time by a circuit, measured in bits/bytes per second or packets per second.

Five Nines

High availability of service, commonly taken to mean 99.999% uptime.

Silent Failure

A

Introduction to Architecture

• Instruction Set Architecture (ISA): An assembly language programmer's view of the microprocessor.
• Assembler: Translates symbolic assembly language code into binary machine language code.

Computer Performance Metrics

• Execution Time (Response Time): Time to complete a program or task.
• Throughput (Bandwidth): Number of programs or tasks completed per time unit.
• Execution Time (t_exec, i.e., elapsed time, wall time, real time, response time): Elapsed seconds from start to finish. Includes:
  • Executing instructions
  • Disk access
  • Memory access
  • I/O activities
  • OS overhead
• User CPU Time (t_cpu(user)): Seconds the CPU spends executing the program's instructions.
• System CPU Time (t_cpu(sys)): Seconds the CPU spends executing OS (kernel) instructions

Certainly! Here is a cheat sheet for computer architecture:

1. Central Processing Unit (CPU)

• The "brain" of the computer that executes instructions.
• Consists of the Control Unit (CU) and the Arithmetic Logic Unit (ALU).
• Fetches instructions from memory, decodes them, and executes them.

2. Memory Hierarchy

• Registers: Fastest and smallest storage units located within the CPU.
• Cache: High-speed memory that stores frequently accessed data.
• Main Memory (RAM): Larger storage used to hold data and instructions.
• Secondary Storage: Non-volatile storage devices like hard drives and SSDs.

3. Instruction Cycle

• Fetch: The CPU fetches the next instruction from memory.
• Decode: The instruction is decoded to determine the operation.
• Execute: The instruction is executed

Building a Sudoku Solver in Java with Backtracking

This document presents a Java implementation of a Sudoku solver, utilizing a classic backtracking algorithm. The code demonstrates how to represent a Sudoku board, check for valid moves, and recursively find a solution to the puzzle.

Initial Sudoku Puzzle Setup

The Sudoku board is represented as a 2D integer array. A value of 0 indicates an empty cell that needs to be filled.

int[][] board = {
  { 8, 0, 0, 0, 0, 0, 0, 0, 0 },
  { 0, 0, 3, 6, 0, 0, 0, 0, 0 },
  { 0, 7, 0, 0, 9, 0, 2, 0, 0 },
  { 0, 5, 0, 0, 0, 7, 0, 0, 0 },
  { 0, 0, 0, 0, 4, 5, 7, 0, 0 },
  { 0, 0, 0, 1, 0, 0, 0, 3, 0 },
  { 0, 0, 1, 0, 0, 0, 0, 6, 8 },
  { 0, 0, 8, 5, 0, 0, 0, 1, 0 },
  { 0, 9, 0, 0, 0, 0, 4, 0, 0 }
};

Implementing

Packet Fragmentation: Layer 3 vs. Layer 2

As mentioned in the “Link-Layer Fragmentation and Interleaving” section, PPP, Frame Relay, ATM, and other WAN technologies support fragmenting packets (frames) at Layer 2. As you may have learned in basic networking classes, IP can also fragment packets at Layer 3. What are some advantages and disadvantages of fragmenting at Layer 3 versus fragmenting at Layer 2?

Advantages and Disadvantages

• Advantages (Layer 3 Fragmentation): Large packets can be transmitted at Layer 2 as fragmentation is done at Layer 3. This reduces the number of acknowledgment exchanges. Also, maintaining the order of fragments to ensure the order of transmission and reassembly is not required.
• Disadvantages (Layer 3 Fragmentation)

Chapter 1 Introduction to Services

3.1. Service Terminology Service

a service is a software program that makes its functionality available via a technical interface, called a service contract.

Figure 3.1. The symbol used to represent an abstract service.

Service Contract

The symbol used to represent a service contract is displayed in Figure 3.2.

Service Capability

A service contract can be broken down into a set of service capabilities, each of which expresses a function offered by the service to other software programs.

Figure 3.4. A Purchase Order service contract with four service capabilities.

Service Consumer

A service consumer is software program when it accesses and invokes a service—or, when it sends a message to a service capability

Service

1. Visibility of System Status

The system should always keep users informed about what is going on, through appropriate feedback within a reasonable time.

2. Match Between System and the Real World

The system should speak the user's language, with words, phrases, and concepts familiar to the user, rather than system-oriented terms. Follow real-world conventions, making information appear in a natural and logical order.

3. User Control and Freedom

Users often choose system functions by mistake and will need a clearly marked "emergency exit" to leave the unwanted state without having to go through an extended dialogue. Support undo and redo.

4. Consistency and Standards

Users should not have to wonder whether different words, situations, or actions... Continue reading "10 Usability Heuristics for User Interface Design" »