Computer Structure, Linux, and Apache

Basic Structure of Computers

• This module aims to help students understand, describe, and explain the fundamentals of network communications and client-server applications.
• An additional benefit is describing basic cloud computing services with hands-on practice on the Linux operating system.
• A Google data center introduction video is linked.
• The principal components of a web application are demonstrated.

Linux Operating System

• A secure and reliable platform for web server operation.
• Governs file system access using file permissions.
• Enforces process and user security.
• Provides network interfaces.

Apache Web Hosting Service

• Receives HTTP requests and interprets their contents.
• Determines if a file extension is supplied.
• Ascertains if the requested resource is static or application-related.
• May need to locate and respond with multiple resources (HTML, CSS, JavaScript, images, media files).
• Determines content location based on the HTTP request path and file paths in the HTML content.

PHP Programming Language

• PHP is a popular scripting language used for various applications including content management systems (CMS) like Joomla, forums, bulletin boards and shopping carts.
• Apache recognizes when a script needs to be run, often through file extensions and default settings.
• For example, Apache seeks an index.php file if a website's home page is requested and PHP is installed.
• PHP scripts store, retrieve information, and render HTML page layouts for transmission back to the user's browser.

MySQL Database

• Typically used by PHP websites to store content and configuration information.
• Offers greater flexibility than storing content in flat text files.
• PHP manages the interaction between the Apache web server and the MySQL database.

Other Components

• Compiled applications for specialized media, graphic content, or rendering images/animations.
• Common applications include email, often provided with a webmail interface via Apache or direct connections using POP, IMAP, and SMTP protocols.

Overview of Computer Concepts

• Most devices in a network involve a computer.
• Obvious devices include workstations, PCs, laptops, and network servers running Windows, Linux, Unix, and macOS.
• Also includes specialized computers such as routers and switches for moving data between computers/networks.

Basic Functions of a Computer

• Input: A user types 'A' on the keyboard, sending a code representing 'A' to the computer.
• Processing: The CPU determines the letter typed by looking up the keyboard code in a table.
• Output: The CPU sends instructions to the graphics card to display the letter 'A' on the monitor.

Components of a Computer

• Input devices: Send data to a computer for interaction and control (e.g., keyboard, mouse).
• Processing devices: Handle information processing within the computer system (e.g., CPU, RAM, hard drive).
• Output devices: Convert data from the system into a human-readable form (e.g., monitor, printer).

Input Components

• Common user-controlled devices include keyboards, microphones, webcams, and scanners.
• External interfaces (serial, FireWire, USB ports) can input data.
• Storage devices (hard disks, CDs/DVDs) can also act as input components.

Processing Components

• CPU (Central Processing Unit): The main processing component executing instructions from programs and the operating system.
• Current CPUs have multiple cores, enabling simultaneous instruction execution for better performance.
• Multi-core CPUs are like a person with two brains

Output Components

• Monitors and printers are the most common output components.
• Storage devices and network cards also function as output components.
• External interfaces (e.g., a USB-connected disk drive) allow writing files to a disk, acting as output.

Storage Components

• More storage generally improves computer performance.
• Most storage components function as both input and output devices.
• Storage includes disk drives, CD/DVD drives, and USB flash drives.
• Storage is divided into short-term and long-term categories.

RAM (Short-Term Storage)

• Temporary storage for instructions and data being processed by the CPU.
• Content is lost when the computer is turned off (volatile memory).
• The amount of RAM is crucial for efficient computer operation.
• It is also known as working storage.

Virtual Memory

• Part of disk storage can be used as virtual memory.
• The CPU can only access data/code in RAM.
• Data/code in virtual memory is moved to RAM when needed by the CPU.

Long-Term Storage

• Maintains data even without power (non-volatile memory).
• Examples include hard disks, CDs/DVDs, and USB flash drives.
• Used to store documents, multimedia files, application and OS files.
• The amount needed depends on the type and quantity of files stored.

Personal Computer Hardware

• Four major components: motherboard, hard drive, RAM, and BIOS/CMOS.

Motherboard Components

• CPU socket: Where the CPU is installed.
• PCI bus expansion slots: For adding functionality via expansion cards.
• PCI Express expansion slots: Supersede PCI, supporting faster data transfer speeds. Larger slots suit graphics cards/disk controllers.
• RAM slots: Install RAM on the motherboard.
• Chipset with heat sinks: North and South Bridge chips control data transfers. The heat sink prevents overheating.
• SATA connectors: Connect hard drives and CD/DVD drives using the Serial ATA specification.
• IDE connectors: Similar function to SATA but outdated.
• Main power connector: Supplies power to the motherboard.

Computer Bus Fundamentals

• A bus consists of wires carrying signals (data, address, control) within the computer.
• All data goes through the motherboard.
• Buses connect CPU and RAM, CPU and disk drives, CPU and expansion slots.

Data Bus

• Carries data signals between the CPU and main memory (RAM), or between main memory and I/O devices.

Address Bus

• Carries address signals specifying memory locations or I/O device interfaces.

Control Bus

• Carries control signals (e.g., read or write) from the CPU to memory or I/O interfaces.

CPU Data Retrieval from RAM

• The CPU requests data from RAM at a specified address via the address bus.
• The address is then sent through the data bus

Differences Between Address and Data Bus

• Data bus: Carries the data to be stored.
• Address bus: Carries the location (address) where the data should be stored.
• The address bus specifies a physical address in memory.
• The data bus carries the actual data.
• When the processor needs to read or write from or to the memory it uses the address bus to specific the physical address of the individual memory block it needs to access.
• The actual data is sent along the data bus.

Data Bus Characteristics

• Bidirectional: Used for both read and write operations.
• Write operation: the processor will put the data to be written onto the data bus.
• Read operation: the memory controller will get the data from the specific memory block and put it into the data bus.

Address Bus Characteristics

• Unidirectional: Addresses are always specified by the processor.

I/O Polling and Interrupt

• External devices (mouse, keyboard, printer, etc.) need CPU attention.
• Interrupt and polling are two ways to handle events generated by these devices.
• Polling and interrupt lets the CPU stop what it is currently doing and respond to the more important task

Polling

• CPU checks I/O devices at regular intervals to see if they need service.

Interrupt

• I/O device interrupts the CPU to request service.

Hard Drive Fundamentals

• Primary long-term storage component.
• Consists of magnetic disks (platters) that store data as magnetic pulses.
• Stores documents, applications, and the OS loaded during boot.

Hard Drive Components

• Actuator arm: Moves the head arm assembly for continuous movement and control.
• Magnetic platters: Circular disks where data is stored as ones and zeros.
• Read/write heads: Read (sense) and write (record) data on the magnetic disk.

Solid State Drives (SSDs)

• Replace hard drives in many modern systems due to high performance, speed, and reliability.
• Use flash memory with no moving parts, providing faster access times.
• More expensive than hard drives.
• Commonly found in mobile devices, high-performance desktops, and servers.

RAM Fundamentals

• Main short-term storage component.
• No moving parts, so data access is faster than on a hard drive.
• More RAM generally results in faster system performance.

BIOS/CMOS Fundamentals

• BIOS (Basic Input Output System): Instructions in a chip on the motherboard.
• BIOS directs the CPU to perform tasks when power is applied.
• A power-on self-test (POST) is one of these tasks.
• CMOS (Complementary Metal-Oxide Semiconductor): Stores hardware configuration, accessible via the BIOS setup utility.

Computer Boot Procedure

• Power is applied to the motherboard.
• The CPU starts.
• The CPU carries out BIOS startup routines, including POST.
• Boot devices (specified in the BIOS configuration) are searched for an OS.
• The OS is loaded into RAM.
• OS services are started.

Fundamentals of Network Communication

• A computer network consists of two or more computers connected by a transmission medium (cable or airwaves).
• A computer must connect to a network to access the internet.

Network Interface Card (NIC) Basics

• Attaching a computer to a network requires a NIC to create and mediate the connection.
• NIC contains a MAC address (Media Access Control address), a unique identifier.
• MAC addresses are assigned by the manufacturer and stored in hardware or firmware.
• Networking media can include copper wire, fiber optic cable, or airwaves.

Wireless NIC

• Selection depends on the type of wireless access point (AP) being used.
• Typical are Wireless-N (802.11n), Wireless-AC (802.11ac), or 802.11a/b/g/n.
• The letters (a/b/g/n/ac) refer to the wireless networking standard the device supports.
• Connects to the network using the Service Set Identifier (SSID).
• A security key, username, and password may be required depending on the network's security configuration.

Types of Computers

• Embedded computers
• Personal computers
• Servers and enterprise systems
• Supercomputers and grid computers
• Cloud computing

Computer Components

• Processor (CPU): Consists of the arithmetic and logic unit (ALU) and control unit.
• These two components are key in making up the processor.