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

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" »

Problem Statement

Explore the usage of basic Linux system calls.

Process Management System Calls

The system calls to manage processes are:

• fork(): Used to create a new process.
• exec(): Executes a new program.
• wait(): Waits until the process finishes execution.
• exit(): Exits from the process.

System calls used to get process IDs are:

• getpid(): Gets the unique process ID of the process.
• getppid(): Gets the parent process's unique ID.

Stat System Call

The stat system call retrieves information about files, specifically from their inodes. For instance, to get a file's size and name, you would typically use stat. Let's illustrate with a C code snippet (src/ls1.c):

#include<stdio.h>
#include<dirent.h>
#include<cstdlib>

struct dirent *dptr;

WEEK 1: Software that Manages Computer Hardware

Operating System as an Abstract Machine, Service Provider, and Resource Manager. OS Objectives: Convenience, Efficiency, and Ability to Evolve.

Performance Indices

Arrival Time, Service Time, Turnaround Time, Normalized Turnaround Time. First-Come-First-Served (FCFS) Scheduling Policy.

Microprocessor and DMA Activity

Impact of Microprocessor Bus Configuration and DMA Activity on System Speed.

Memory System and Cache

Cache and Main Memory Access Time, Average Access Time Calculation.

iOS and Android

Similarities and Differences between iOS and Android.

Job Execution and CPU Utilization

CPU Utilization for Uniprogramming and Multiprogramming.

Direct Memory Access (DMA)

Coordination, Memory Operations Completion,... Continue reading "Understanding Operating Systems: Functions, Performance, and Multithreading" »

Web Design & Development

Common Terms

Web Design

Is the act or practice of determining how a website looks.

Web Development

Is the act or practice of determining how a website works.

Navigation

Is the act of using and finding things on a website.

CSS

(Cascading Style Sheets) is a simple language that decides how a web page looks.

Coding

Is the programming language that makes up a website.

Visibility

Is how easily people find a website using search engines, based on how many other websites link to it.

Usability

Is how easy it is for a person to use a website.

Content

Is the material on a web page, including text and graphics.

Appearance

Is how a web page looks.

Functionality

Is the ability of different elements of a website to work together.

Programming Languages

C

Is... Continue reading "Web Design & Development Glossary: Terms and Definitions" »

Chapter 3: Statelessness

This means that each request from a service consumer should contain all the necessary information for the service to understand the meaning of the request. All session state data should then be returned to the service consumer at the end of each request.

Figure 5.2. Statelessness ensures that each service consumer request can be treated independently by the service.

1. Cookies: Temporary data stored on the client-side, encrypted if SSL is used.

2. Types of Certificates:

• Site
• Personal
• Software Vendor
• Anonymous

3. Identity: Used for:

• Authentication
• Accountability
• Identifying principle

4. Principal: A unique identity. Identity is used to identify the principal, which is a computer representation of an entity.

5. Goals of a Certificate Regarding Identity: To bind the correct identity to a distinguished name.

6. Malicious Logic: A set of instructions that cause a site's security policy to be violated.

7. Predictable Computer Usage Patterns: Yes, my usage is statistically predictable. I often work from home, so the patterns between work and home are similar. I check email, run the browser, run Visual Studio, NetBeans, a... Continue reading "Security Essentials: Certificates, Identity, and Access Control" »

To start a backend project.

- npm init

Then make a file with whatever entry point you named it as, for example, server.js

Once package.json is created:

• npm i <package>
• connect-mongo (store sessions in DB)
• dotenv (for config files, environment variables)
• express
• mongoose
• express-sessions (sessions and cookies)
• method-override (to use PUT, UPDATE, DELETE requests)
• moments (date formatting)
• morgan (logging)
• passport (authentication)

npm i -D <package>

• nodemon (Update every file change instantly without having to restart the server)
• cross-env (To update environment variables in script definition itself)

After installing the dependencies, edit the scripts in package.json

Instructions:

1. Refer to the files using a relative path.
2. Save all files, including the HTML file, before using this feature.

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