Notes, abstracts, papers, exams and problems of Computers

Understanding Computer Security

Common Threats

• Worm: Designed to replicate itself, a worm operates as a standalone application, unlike a virus.
• Trojan: Disguised as a legitimate program (e.g., a screensaver), a Trojan operates covertly to inflict damage.
• Phishing: Attackers impersonate trustworthy entities to steal sensitive information, exploiting social engineering tactics.

Network and Security Concepts

• Simple Mail Transfer Protocol (SMTP): A standard for email communication, SMTP is known for its lack of robust security.
• Sandboxes: Software environments that isolate programs to prevent them from harming the host system, commonly used in web browsers.

Wireless Security

• Wireless Internet (Wi-Fi): Enables wireless communication between devices, forming

Network Classification by Device Roles

Networks can be classified based on the roles of the devices within them:

• Client-Server: This is the most common type. A powerful server provides services to multiple clients and is always available. Example: A web server.
• Peer-to-Peer: In this model, all computers have equal roles and share resources directly. Example: BitTorrent.

Router Functions in Home Networks

Routers provided by Internet Service Providers (ISPs) often integrate the functions of multiple devices, including:

• Hub
• Modem
• Access Point

MAC Address Translation

The MAC address 08-2E-5F-14-93-A0 in decimal is 8-46-95-20-147-160.

Switches and the OSI Model

Switches operate at Level 2 (Data Link Layer) of the OSI model. Other devices that work at this level... Continue reading "Network Types, MAC Addresses, and OSI Model Explained" »

What is a Process?

A process is a program in execution, encompassing the current values of the program counter, registers, and variables. It's an active entity with a limited lifespan, created at execution start and terminated upon completion. Processes utilize various resources like memory, disk, and printers as needed.

Process vs. Program

Multiprogramming and the Process Model

Multiprogramming involves rapidly switching the CPU between multiple... Continue reading "Processes, Threads, and RAID Levels in Operating Systems" »

Telephone Means and Equipment

Fixed individual devices (copper networks have been replaced by optical fiber networks)

Private branch exchanges (PBX): it connects calls between two destinations or ends

Function: call transfers among extensions, caller ID…

Types: IP PBXs call centers, they manage just phone calls contact centres, they not only manage phone calls but emails, SMS, online messages, faxes, etc.

Mobile devices: PDA, Smartphone

Services: Internet, e-mail, videoconference, digital camera, audio an Video quality player, an agenda, GPS, own, Operating system

Additional services offered by the telephone equipment

Common features

A.Fixed telephony: -Notice of charge(aviso de cargo) you receive info on the cost of a call Call forwarding(desvio

Intranet:=Internet is private network which operated by large company which use internet topologies and it is globle.

Extranet:=Extranet is an intranet that is accessible to some people from outside the company.

Internet:=It is a worldwide system of computer network.

Intranet exteanet:

An intranet is a private network, operated by a large company or other organisation, which uses internet technologies, but is insulated from the global internet. An extranet is an intranet that is accessible to some people from outside the company, or possibly shared by more than one organisation

The major difference from an extranet, however, is that an intranet is used internally. While an extranet allows businesses to communicate with clients and vendors,... Continue reading "j" »

Framing bit stuffing:

Framing in Computer Network. Data link layer is responsible for something called Bit Stuffing in Computer Network. It is the division of stream of bits from network layer into manageable units (called frames). Frames could be of fixed size or variable size. Bit stuffing is the insertion of non-information bits into data.

framing: A frame is a digital data transmission unit in computer networking and telecommunication.

Bit Stuffing: Bit stuffing is the process of inserting non-information bits into data to break up bit patterns to affect the transmission of the network.

Byte Stuffing: It is a process that transforms a sequence of data bytes that may contain illegal or reserved values.

Memory Management Problems and Solutions

Deadlock Scenario

A system has four processes and five allocable resources. The current allocation and maximum needs are as follows:

What is the smallest value of x for which this is a safe state?

The needs matrix is as follows:

• 0 1 0 0 1
• 0 2 1 0 0
• 1 0 3 0 0
• 0 0 1 1 1

If x is 0, we have a deadlock immediately. If x is 1, process D can run to completion. When D is finished, the available vector is 1 1 2 2 1. Now, A has ‘10211’ and ‘11221’ is available which together satisfies maximum need. So, A is finished and now ‘2 1 4 3 2’ is available, which can satisfy C. Once C is done, the available resources are 3 2 4 4 2, which can help B finish. So, x =1 will do.

Memory Compaction

A swapping system eliminates... Continue reading "Memory Management: Algorithms and Techniques" »

TEXTO 1 • TELEGRAPH

Telegraph, an electrically operated device or system for distant communication (the first ever invented) by means of visible or audible signals. The method used throughout most of the world, based in large part on the mid-19th-century work of Samuel F.B. Morse, utilizes an electric circuit set up customarily by using a single overhead wire and employing the earth as the other conductor to complete the circuit. In the telegraph's simplest form, an electromagnet in the receiver is activated by alternately making and breaking the circuit. Reception by sound, with the Morse code signals received as audible clicks, is the basis for a low-cost, reliable method of signaling. In addition to wires and cables, telegraph messages... Continue reading "History and Function of Telegraph, Cellular Telephone, and Computer" »

5. A machine has a 32-bit address space and an 8-KB page. The page table is entirely in hardware, with one 32-bit word per entry. When a process starts, the page table is copied to the hardware from memory, at one word every 100 nsec. Lf each process runs for 100 msec (including the time to load the page table), what fraction of the CPU time is devoted to loading the page tables?

The page table contains 232 /213 entries, which is 524,288.  Loading the page table takes 52 msec. If a process gets 100 msec, this consists of 52 msec for loading the page table and 48 msec for running. Thus 52% of the time is spent loading page tables.

6. Suppose that a machine has 48-bit virtual addresses and 32-bit physical addresses. If pages are 4 KB, how many... Continue reading "Understanding Paging and Virtual Memory in Computer Architecture" »

Traffic Server Client Request and Response API Functions

This document describes the Traffic Server API functions related to client requests and responses.

Client Request Functions