Server

What Is a Server?

Simply put, a server is a data storage location on a network.
The word server has the meaning of “a place that provides.” A computer that provides corresponding data in response to user demands (requests) through a network such as the Internet is called a “server.”
Servers are used for all Internet-related services, such as browsing web pages, mail, SNS, and online shopping.

Server and Client

In a network, the side that provides data is called the server, and the side that uses data is called the client.
When browsing a website or sending mail, data files such as video files or HTML files are returned from the server in response to requests from the client.
The main role of a server is to send processed files or store data according to client requests.

Upload and Download

Providing information from a client to a server is called “upload.”
(Example) Posting a video to a video sharing site, uploading a photo to SNS

On the other hand, receiving a file from the server that provides it is called “download.”
(Example) Bringing images and videos published on the Internet into a computer

How Servers and Networks Work

To help visualize the role of a server, let’s use the flow from creating a homepage to having visitors view it as an example.

Upload Homepage Data to a Server

Simply having homepage data on your own PC is not enough to show it to Internet users.
To make the homepage viewable, the homepage data must be stored on a server.

When a User Enters a URL in a Browser, a Request Reaches the Server

When an Internet user enters the homepage URL into a browser such as Google Chrome and presses Enter, a request is sent to the server.

URL
- A string that indicates the location of a web page; it is also called an address.
- The URL of the top page of the current site is “https://www.devkuma.com.”
Browser
- Software for viewing homepages (websites) on a PC or smartphone through the Internet.
- Google Chrome, Safari, and Internet Explorer are well-known examples.

The Server Provides Data to the User’s PC or Smartphone According to the Request

The server retrieves the page data that corresponds to the URL and provides files such as HTML and images to the user’s PC, smartphone, or other device.

In addition, to make the site accessible through search engines such as Google or Naver, it is necessary not only to upload homepage data to the server, but also to index (register) it.
Simply uploading homepage data to the server does not make the site appear in searches on Google, Naver, and similar services.
To allow users to access the site through search engines instead of directly entering the URL in the browser, it is essential to index the homepage data in the search engine’s database.

Server Types

Servers as computers can be broadly divided into two types: “physical servers” and “virtual servers.”

Physical Server

A physically existing single server can be divided into two types: “shared server” and “dedicated server.”

Dedicated Server

A dedicated server is a server used exclusively by one user. It has the advantage of a high degree of freedom, such as not being affected by other users and being able to customize the OS, but operating it with proper customization requires a certain level of expertise.

Shared Server

This is a rental server where multiple users share and use a single physical server. It has the advantages of lower cost and less maintenance effort, but because multiple users share it, customization is not easy. Processing can be affected by other users’ usage, and if the server fails, many users can be affected.

Virtual Server

A virtual server is a server that runs multiple operating systems on one physical server and operates them as multiple servers. It can be divided into two types: “VPS” and “cloud server.”

VPS Server

VPS stands for Virtual Private Server and is also called a virtual dedicated server.
Like a shared server, it shares one physical server, but because each environment is built virtually and separately, it has the advantage of being less affected by other users and offers high customizability.

Cloud Server

A cloud server is a server created in a cloud environment. Like a VPS, it builds a virtual dedicated server, but compared with a VPS, where resources such as server capacity and processing performance are fixed by plan, a cloud server has the characteristic of high flexibility because resources are not fixed and can be increased quickly when access unexpectedly surges. Representative examples include AWS and GCP.

Server Uses

The four types of servers introduced above are servers as computers.
By contrast, servers as software provide various functions depending on their purpose.

Web Server

A web server returns data on the web to clients according to requests from clients. It includes HTML files that make up a website (homepage), CSS files that adjust the page structure and design, image files, and similar resources. When a client requests stored web page information, the server returns and sends the corresponding data.

Mail Server

A mail server is used when sending and receiving mail.
Servers are divided into sending and receiving roles. SMTP servers are used as sending servers, and IMAP or POP3 servers are used as receiving servers. The reason mail can be received without problems after turning the power back on, even if mail was sent while the power was off, is that the incoming mail data is stored inside the mail server.

Difference Between POP3 Servers and IMAP Servers

The major difference between POP3 servers and IMAP servers is whether mail data continues to be stored on the server. With a POP3 server, mail data is stored on the server at first, but when it is received by mail software, the data is downloaded to the PC or smartphone and then deleted from the server. The reason you can read mail received in the past even when not connected to the network is that the mail data is stored on the device. On the other hand, an IMAP server leaves data on the server. Therefore, when using multiple devices such as PCs and smartphones, the same mail can be read. In Gmail or Naver Mail, the reason you can read the same mail from any device after logging in is that an IMAP server is used.

DNS Server

A DNS (Domain Name System) server is used to connect IP addresses and domains.
An IP address is a unique number assigned to a device connected to a network and is like an address on the web. However, because a string of numbers is difficult for people to remember, a domain is the name attached to that string of numbers.

For domains and DNS servers, the explanatory manga distributed by JPRS (Japan Registry Services Co., Ltd.), a company that manages jp domains nationwide, is easy to understand.

File Server

A file server is used to share and use data on a network.
Through a file server, data sharing can be performed smoothly across multiple servers and various operating systems.

Database Server

A database server is a server equipped with a database and running a database management system. It receives requests from clients, searches organized information in the database, and sends processing results back.

FTP Server

An FTP (File Transfer Protocol) server is also called a “file transfer protocol” server and is used to send and receive files to and from a web server.
Unlike a web server that sends files only when there is a request, an FTP server allows uploads from a client to a server and downloads from a server. When creating a website, an FTP server is used to upload new files to a web server.

SSH Server

An SSH (Secure Shell) server is a server that encrypts client information.
In early remote communication methods, personal information was not encrypted, so information could sometimes leak. When sending personal information such as passwords or passcodes, SSH servers made it possible to encrypt the information first and then send it remotely and safely.