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

Managing operating systems on workstations boils down to three basic tasks: loading the system
software and applications initially, updating the system software and applications, and
configuring network parameters.
We call these tasks the Big Three.

The Five States

The diagram depicts five states: new, clean, configured,
unknown, and off.

• New refers to a completely new machine.
• Clean refers to a machine on which the OS has been installed
  but no localizations performed.
• Configured means a correctly configured and operational
  environment.
• Unknown is a computer that has been misconfigured or has
  become out of date.
• Off refers to a machine that has been retired and powered off.

Transitioning Between States

There are many ways to get from one lifestyle... Continue reading "Managing Operating Systems on Workstations: The Big Three" »

Set Cover to Efficient Recruiting

Input: Set U of elements, collection S₁, ..., S_m of subsets of U, integer k ≥ 0

Construct an instance of the Efficient Recruitment Problem:

• Sports are represented by U.
• Applicants are represented by {1, ..., m}.
• For every s ∈ U and 1 ≤ i ≤ m, M[s, i] = 'qualified' if s ∈ S_i and 'not qualified' otherwise.

Steps:

1. Call the oracle for Efficient Recruiting with input M and k.
2. Return the result (yes or no) of the previous call.

Vertex Cover and Hitting Set

Graph: G = (V, E)

• U = V(G)
• S_i = {u, v}, where (u, v) is an edge of G.

Vertex Cover ⇒ Hitting Set:

If C is a vertex cover for G of size k, then by definition, for every edge (u, v) in G, either u ∈ C or v ∈ C. Therefore, C is a solution for Hitting Set because... Continue reading "Efficient Recruiting and Algorithm Design: Set Cover, Hamiltonian Path, and Longest Increasing Subsequence" »

Dynamic Host Configuration Protocol (DHCP) Servers

What is a DHCP Server?

A DHCP Server is a network server that automatically provides and assigns IP addresses, default gateways, and other network parameters to client devices. It relies on the standard protocol known as Dynamic Host Configuration Protocol (DHCP) to respond to broadcast queries by clients.

Benefits of DHCP

A DHCP server automatically sends the required network parameters for clients to properly communicate on the network. Without it, the network administrator has to manually set up every client that joins the network, which can be cumbersome, especially in large networks. DHCP servers usually assign each client with a unique dynamic IP address, which changes when the client’s... Continue reading "Network Fundamentals: DHCP, Subnetting, and Transport Protocols" »

This section details the implementation of the Jacobi method in Fortran for solving a system of linear equations. The subroutine solucion_Jacobi takes a matrix A, a vector b, and an initial guess X as input, and returns the solution vector X.

Subroutine: solucion_Jacobi(A, b, X)

The subroutine begins with the following declarations and initializations:

• use normas
• integer, parameter :: Kx = 100
• real(8), parameter :: tolerancia = 1E-6
• real(8), allocatable :: X0(:), ERROR(:)
• real(8), intent(in) :: A(:,:), b(:)
• real(8), allocatable, intent(out) :: X(:)
• integer :: i, j, k, n
• real(8) :: sum, zero, ek

Where:

• Kx is the maximum number of iterations.
• tolerancia is the error tolerance.
• X0 is the previous iteration's solution vector.
• ERROR is the error vector.
• A is the

Binary Conversion

Single-Precision Floating-Point

Format: 1 sign bit, 8 exponent bits, 23 fraction bits

Bias: +127 (decimal to binary), -127 (binary to decimal)

Double-Precision Floating-Point

Format: 1 sign bit, 11 exponent bits, 52 fraction bits

Bias: +1023 (decimal to binary), -1023 (binary to decimal)

Example: -17.6875 (Single-Precision)

1. Sign Bit: + = 0, - = 1 (In this case, 1)
2. Integer Part to Binary: Repeatedly divide the integer part by 2 and record the remainders.
3. Fractional Part to Binary: Repeatedly multiply the fractional part by 2 and record the integer parts.
4. Combine and Normalize: Combine the binary integer and fractional parts. Normalize to the form 1.xxx * 2^exponent.
5. Calculate Exponent: Add the bias to the exponent.

Intra-AS Routing

RIP – Based on Distance-Vector (D-V), fewer messages, converges slower, smaller size.

OSPF – Based on Link-State (L-S), converges faster, more messages, larger networks.

Distance-Vector is distributed, and each router only knows the costs to its neighbors and their distance vectors.

Link state is global and requires that each router knows the network topology and link costs to all nodes.

OSPF: Used internally inside a network, an intra-network/domain protocol used in an AS.

BGP: An internetwork protocol used between two different ASs, used at the edge of your network to connect your network to the internet.

RIP: An intra-network protocol used in an AS, used for small networks (maximum number of hops is 16).

EBGP: Runs between two... Continue reading "Routing Protocols: RIP, OSPF, BGP, CSMA/CD, CSMA/CA" »

1. Make quality #1

   Quality must be quantified and mechanisms put into place to motivate its achievement. Defining quality commensurate with the project at hand is important but is not easily done at the outset of a project.

2. Involve the customer

   Techniques that have been demonstrated to increase quality include involving the customer, prototyping, simplifying design, conducting inspections, and hiring the best people. This principle is mostly redundant.

3. Give products to customers early

   No matter how hard you try to learn users' needs during the requirements phase, the most effective way to determine real needs is to give users a product and let them play with it.

4. Determine the problem before writing the requirements

   When faced with what they believe is

• Accuracy

  Tells us how correct a GPS measurement is.

• Array

  A group of disk drives that are connected and used as a single unit.

• Assembler

  A program that translates low-level programming language into machine code.

• Attachment

  A file sent as part of an email.

• Avatar

  An image in a computer game that represents a person.

• Barcode

  An arrangement of lines and spaces that represent data.

• Bit

  The smallest unit of computer data.

• Bitrate

  A measurement of the amount of data that is processed.

• Broadband

  A system that allows computers to transfer large amounts of information.

• Calibration

  The act of adjusting printers and scanners to display colors correctly.

• Capacity

  The amount of space an MP3 player has to store files.

• Catalog

  An inventory of books in a library.

• Cell phone

  A wireless

1. Why Can IEEE 802.11 Transmit Further Than Bluetooth?

IEEE 802.11 (Wi-Fi) has a higher power output than Bluetooth.

2. Three Advantages of Wireless Over Wired Technology

• Anytime, anywhere connectivity
• Easy and inexpensive to install
• Ease of adding additional devices

3. Two Benefits of Wireless Networks Over Wired Networks

• Mobility
• Reduced installation time

4. Factors Affecting the Number of Access Points Needed

Three factors that affect the number of access points needed for wireless connectivity are:

• The size of the building
• The number of solid interior walls in the building
• The presence of microwave ovens in various offices

5. Why is Security Important in Wireless Networks?

Security is crucial because wireless networks broadcast data over a medium that