Notes, abstracts, papers, exams and problems of Computers

Parbegin / Person Learns

Parbegin is a structure to indicate parallel execution, marking the beginning and end. Selection: A statement dividing sequential execution into parallel streams.

Its general form (Dijkstra):

parbegin Proposition1; Proposition2; Proposition n; person learns

Mutex

Mutex occurs when processes share data, preventing simultaneous access. It applies when a process accesses shared data, allowing concurrent execution of non-conflicting transactions.

Critical Sections

A process accessing shared data is in a critical section. When a process is in a critical section:

• All other processes are excluded from their critical sections.
• Other processes can execute outside their critical sections.
• When a process exits, the next waiting process

Database Queries

Queries are objects in a database that allow you to filter data in a table or query. They display data from a table that meet specified criteria.

Selection Queries

Selection Queries extract or show only the data that you specify. The results can be used to modify the data.

Action Queries

Action Queries make changes to records in a single operation. Types include delete, update, append, and create tables.

Creating a Selection Query

To create a select query, follow these steps:

1. Open the database where you want to create the query.
2. Click the Query object to the right of the database window.
3. Click the New button in the database window.
4. Select Design View.
5. Click the OK button.
6. Select the table to query.
7. Click the Add button.
8. For queries from multiple

Runtime Memory Organization

The organization of memory at runtime depends on the type of language (declarative, imperative), the compiler, and the operating system.

General Structure of Programming Languages

When you run a program, the OS loader allocates the required amount of memory and loads the code to be executed (stored in a file) into the code area.

The OS should detect collisions between the stack and the heap. In these cases, the program may abort, or the amount of allocated memory may be increased.

In memory paging systems, the above scheme can be fragmented and scattered between real memory and the virtual memory system.

Any reference to a storage location within the code should be relative to the position assigned to the process by the... Continue reading "Runtime Memory Organization: Code, Static Memory" »

1. Expansion Cards

Utility

Expansion cards add new features or improve existing ones in a computer. They facilitate communication between internal and external peripheral devices and the system bus.

Disk Controller Card

Disk controller cards, once used to manage hard disks, CD-ROMs, DVDs, and floppy drives, are now integrated into the motherboard.

Video Card

The video card is crucial for displaying text, images, and graphics on the monitor.

Components

• Video Processor: Receives, processes, and stores information in video memory, transmitting it to the monitor via the VGA connector.
• Memory Chips: Hold information needed to display pixels on the screen.
• AGP: Allows the card to be inserted into the AGP slot.
• Port for the Monitor: Connects the card to the

Turing's Thesis and the Problem of Computability

Thesis 1

"Every problem that can be solved algorithmically can be solved by a Turing machine."

Concepts Associated with Thesis 1

• Algorithm: A set of rules that can be mechanically applied to solve a problem of a given class. Mainly used in mathematical contexts.
• Calculation: Any transaction which is carried out by manipulation of symbols as a means of representation. The symbolic operations are atomic, that is, quite simple, and are held in a computer. The action of the computer will depend on the symbols that have the system and the internal state in which the computer is.

Thesis 2

"Every computable function can be computed by a Turing machine. Every problem that can be solved by algorithmic methods

Process Planning

Objectives

• Justice: Avoid favoring some processes over others.
• Maximum Number of Interactive Users: Focus on most time-sharing systems.
• Predictability: The strategy must enable the execution of processes.
• Minimizing Overhead: Minimize context switches.
• Balance in the Use of Resources: Resources must be used fairly and for as long as possible.
• Safety Priorities: Established priorities should be respected.
• Maximum Capacity of Execution: Minimize process changes.

Criteria

• Response Time: Speed with which the system responds to a request.
• Service Time: Response time minus time for I/O.
• Runtime: Service time minus timeout.
• Processor Time: Processor time occupation.
• Timeout: Waiting times in queues.
• Efficiency: Processor utilization.
• Yield: Number

SPC Control System

SPC Control System refers to the method of controlling a switching system.

• Centralized SPC Control: If a given processor has direct access to all resources of the node and performs all system functions. This usually means the node has a single central computer (doubled for security).
• Distributed SPC Control: If a processor is in a given state but does not have access to some of the resources and/or is not able to run only some of the functions of the system. In practice, this leads to an existing digital system with a high number of microprocessors that perform the control node as a whole.

Functions of Switching Systems

Switching systems provide power and signaling with user terminals. The user, via the wire pair of the switching... Continue reading "SPC Control Systems: Centralized vs. Distributed" »

Database Architecture

The definition of an information system is the detailed description of the system architecture.

Internal Level

The lowest level of abstraction, defining how data is stored on hardware and accessed. Responsibilities of the Database Administrator (DBA) include managing:

• Block size
• Relative position of stored records
• Addressing methods
• Overflows
• Indexing
• Storage changes
• Compression techniques

Conceptual Level

The mid-level of abstraction, representing the organization's data. This level encompasses partial views of different users' requirements and potential uses. It provides a total organizational vision, including data definitions and relationships. DBA responsibilities include:

• Defining the data stored in the database:
  • Data name
  • Attributes
  • Relationships

Software Architecture Design Principles

Key aspects of software design include:

• Software Architecture Design: Defines the major structural components of the software and their relationships.
• Project Data Design: Involves designing the data structure needed to implement the software.
• Procedural Design: Refines and details the procedural description of the structural components defined in the software architecture.
• Interface Design: Describes how software communicates internally (internal interfaces), with other systems (external interfaces), and with users (user interface).

Component vs. Class Diagrams in UML

Similarities

• Both can realize a set of interfaces.
• Both can participate in various relationships (dependency, generalization, association).
• Both