Computer Science

Operating Systems

BIOS

The BIOS (Basic Input/Output System) is the first operating system that runs when the computer starts up. It allows viewing the characteristics of the components and changing their properties.

GRUB

GRUB (Grand Unified Bootloader) is the boot system that links the Linux kernel with the operating systems located on the hard drive.

Application Ports

Difference Between Ports

• Hardware port: Refers to the physical interface where a cable must be connected.
• Software port: A point of entry for communication using a specific protocol.

The software port is also called an application port because it matches a 16-bit coded number (ranging from 1 to 65536) with an application.

Main Ports

• Port 21: FTP protocol – A file transfer protocol.
• Port 22: SSH protocol – Used for almost all remote machine connections. It encrypts exchanges to make intercepted information unreadable.
• Ports 25, 465, 587: SMTP protocol – A protocol for sending messages.
• Port 53: DNS protocol – Matches an IP address with a domain name and vice versa.
• Port 67 (server), 68 (client): DHCP protocol – Automatically assigns an IP address (and associated addressing configurations such as subnet mask and gateway address) to a node on the network that requests it.

SMTP Protocol

The SMTP (Simple Mail Transfer Protocol) is the protocol to configure when creating and setting up an email management server (sending). Its default port is 25.

To receive emails on a client (such as Thunderbird or Outlook), the following protocols can be used:

• IMAP4: Allows viewing and making changes directly on the mail server from the client. Only message headers are downloaded. Its default port is 143.
• POP3: Downloads a copy of messages to the computer. This allows working without an internet connection, but a connection is needed to sync new messages. It communicates on port 110.

DNS

The DNS (Domain Name System) service is essential for accessing the internet. When the IP address of a website is unknown, the DNS converts the domain name into an IP address and vice versa.

TLD (Top Level Domain)

TLDs are the extensions at the end of a URL that uniquely identify a FQDN (Fully Qualified Domain Name), which is the complete domain name (including the extension).

Types of DNS Records

• A – Matches an IPv4 address with a domain name.
• AAAA – Matches an IPv6 address with a domain name.
• CNAME – An alias that links a name to another, usually longer or more complex name.
• MX – MX (Mail Exchanger) records link a given name with the mail server for sending emails.

VNC

VNC (Virtual Network Computing) – A complete solution with detailed settings that allows remote access to troubleshoot a machine (not to be confused with VLC media player).