Server (computing)
{{Refimprove|date=July 2008}}{{Cleanup|date=August 2008}}
A
server is a
computer dedicated to providing one or more services over a computer network, typically through a request-response routine. These services are furnished by specialized server applications, which are
computer programs designed to handle multiple concurrent requests.
(1) Examples of server applications include
mail servers,
file servers,
web servers, and
proxy servers.
Usage in information technology
In Software
Server used as an adjective, as in
server operating system, refers to the product's ability to handle multiple requests, and is said to be "server-grade". A server
operating system is intended or better enabled to run server applications. The differences between the server and
workstation versions of a product can vary from the removal of an arbitrary software limits due to licensing, as in the case of
Windows 2000, or the addition of bundled applications as in
Mac OS X Server.
In Hardware
A
server can also refer to a computer that has been set aside to run a specific server application. For example, when the
software Apache HTTP Server is used as the
web server for a company's website, the computer running Apache is also called the web server. Server applications can be divided among server computers over an extreme range, depending upon the workload.
Server is also used as a designation for computer models intended for use in running server applications under heavy workloads, also called operating units often unattended and for an extended period of time. While any workstation computer is capable of acting as a server, a server computer usually has special features intended to make it more suitable. These features can include a faster
CPU, faster and more plentiful
RAM, and larger
hard drives. More obvious distinctions include redundancy in power supplies, network connections, and
storage devices as well as the
modular design of so-called
Blade servers often used in
server farms.A
server appliance refers to network-connected
computer appliances or "appliance hardware" that provide specific, dedicated applications to a network. Use of the term appliance indicates the marriage of software and hardware in a single system that is not heavily customizable such as
Google Search Appliance. Such appliances are expected to work out-of-the-box with little customization and sometimes remain the sole property of the company that produced them. The simplest appliances include
switches,
routers,
gateways, and
print servers.
Server hardware
missing image!
- My Opera Server Back.jpg -
A server rack seen from the back
Hardware requirements for servers vary, depending on the server application. Absolute CPU speed is not as critical to a server as it is to a desktop. Servers' duties to provide service to many users over a network lead to different requirements like fast network connections and high I/O throughput. Since servers are typically accessed over a network, servers emphasize function over form, without regard to aesthetics like appearance and noise level, because users may never lay eyes on the machine itself. Servers may accordingly run in
headless mode without a
monitor in order to free up processing
cycles for other tasks. In general, a server becomes more specialized and therefore more efficient as unnecessary and unused services are eliminated. For this reason, many servers lack a
graphical user interface, or GUI, because it consumes resources that could be allocated elsewhere. Similarly, servers often lack audio and
USB interfaces.By definition, servers provide services, but it is not always possible to predict when users will need those services. For this reason, servers are often
online for weeks or months without interruption, making hardware durability extremely important. Although servers can be built from commodity computer parts,
mission-critical servers use specialized hardware with low
failure rates in order to maximize
uptime.For example, servers may incorporate faster, higher-capacity hard drives, larger
computer fans or
water cooling to help remove heat, and
uninterruptible power supplies that ensure the servers continue to function in the event of a power failure. These components offer higher performance and reliability at a correspondingly higher price. The dominant paradigm in servers is
parallel computing, and thus
high-performance servers are often placed in
rack-mounted configurations to save space inside
server rooms or "closets." These special rooms help mute the large amount of noise produced and also restrict
physical access to the
system administrators for security purposes.Servers have a unique property in that, the more powerful and complex the system, the longer it takes for the hardware to turn on and begin loading the operating system. Servers often do extensive
preboot memory testing and verification and start up of remote management services. The
hard drive controllers then start up banks of drives sequentially, rather than all at once, so as not to overload the power supply, and afterwards they initiate
RAID system prechecks for correct operation of redundancy. It is not uncommon for a machine to take several minutes to turn on and yet not require a restart for the next calendar year.
Server operating system
Some popular operating systems for servers — such as
FreeBSD,
Solaris, and
Linux — are derived from or are similar to
UNIX. UNIX was originally a
minicomputer operating system, and as servers gradually replaced traditional minicomputers, UNIX was a logical and efficient choice of operating system for the servers. UNIX-based systems, many of which are free in
both senses, are the most popular.Server-oriented operating systems tend to have certain features in common that make them more suitable for the server environment, such as
- an optional or absent GUI,
- ability to reconfigure both hardware and software to some extent without restart,
- advanced backup facilities to permit online backups of critical data at regular and frequent intervals,
- transparent data transfer between different volumes or devices,
- flexible and advanced networking capabilities,
- automation capabilities like daemons in UNIX and services in Windows, and
- tight system security, with advanced user, resource, data, and memory protection.
Server-oriented operating systems can in many cases interact with hardware sensors to detect conditions such as overheating, processor and disk failure, and consequently alert an operator and/or take remedial measures itself.Because the requirements of servers are, in some cases, almost diametrically opposed to those of desktop computers, {{Fact|date=June 2008}} it is extremely difficult to design an operating system that handles both environments well; thus, operating systems that are well suited to the desktop may not be ideal for servers and vice versa. Regardless of OS vendor, system configurations that are ideal for servers may be unsatisfactory for desktop use, and configurations that perform well on the desktop may leave much to be desired on servers. This results in many operating systems' release in both server and desktop versions. Nevertheless, the desktop versions of the Windows and Mac OS X operating systems are deployed on a minority of servers, as are some proprietary
mainframe operating systems, such as
z/OS. The dominant operating systems among servers are UNIX-based and
open source kernel distributions.{{Fact|date=June 2008}}The rise of the
microprocessor-based server was facilitated by the development of Unix to run on the
x86 microprocessor
architecture. The Microsoft Windows family of operating systems also runs on x86 hardware, and versions beginning with
Windows NT have incorporated features that making them suitable for use as server operating systems.While the role of server and desktop operating systems remains distinct, improvements in the reliability of both hardware and operating systems have blurred the distinction between the two classes. Today, many desktop and server operating systems share similar
code bases, differing mostly in configuration. The shift towards
web applications and
middleware platforms has also lessened the demand for specialist application servers.
Servers on the Internet
Almost the entire structure of the
Internet is based upon a
client-server model. High-level
root nameservers,
DNS servers, and routers direct the traffic on the internet. There are millions of servers connected to the Internet, running continuously throughout the world.Among the many services provided by Internet servers are:
Virtually every action taken by an ordinary
Internet user requires one or more interactions with one or more servers.There are also technologies that operate on an
inter-server level.
Servers in daily life
Any computer or device serving out applications or services can technically be called a server. In an office or enterprise environment, the network server is easy to identify. A
DSL/
Cable modem router qualifies as a server because it provides a computer with application services like
IP address assignment (via
DHCP) and
NAT, which is the
firewall that helps protect a computer external threats.
iTunes software implements a
music server to stream music between computers. Many home users create shared folders and printers. Another example are the many private servers for such hosting online games such as
Everquest,
World of Warcraft,
Counter-Strike and
EVE-Online, which is currently hosted on the largest server used in the game industry.
References
-
[RFC 2616 - Hypertext Transfer Protocol -- HTTP/1.1]
{{Computer sizes}}
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