As a host computer (also host computer , the host computer or host computer ; loan translations of English host computer ), short- host , into one is computer network eingebundener computer with associated operating system called, the clients served or Server hosts (ie services provides).
From a historical point of view, the term host refers to a multi-user computer that provides computing power for terminals with the help of applications in the background . After computer networks conquered everyday life in the 1980s, the term was also used for computers integrated in a computer network that provide services for mostly smaller or less powerful systems.
In addition to more powerful operating systems , less powerful systems - for mini-computers or network devices such as routers and print servers - can also serve as hosts . For example, any system that can obtain its network configuration through the Dynamic Host Configuration Protocol (DHCP) is a client of a DHCP server .
Origin of the term
The out of the English borrowed expression host is the EDP early in the 1960s in connection with mainframes or mid-range systems and there usual time-sharing or multi-user - operating systems used. These systems are highly structured and essentially consist of a central unit, which is also known as the host and houses all of the “intelligence”, and the “stupid” terminals that are only used as user terminals at the workstations and practically only for input and output Data serve. The term server, which is often used as a synonym, is more recent and comes from the field of personal computers and operating systems such as Banyan Vines , Mac OS , NetWare or Unix . When the networking of this computer class found its way into practically everywhere at the end of the 1980s, an alternative name was sought to distinguish it from the existing host-based architectures and the term server was established for this . The architectures based on personal computers typically do not have any “intelligent” hosts - in contrast to “stupid” terminals, here every system is equipped with more or less “intelligence”. In this context, computer systems ( hardware and software ) that essentially provide services to other systems (see also: Server (software) ) are referred to as servers . In the Unix environment, the differentiation is clearer at this time, here (mostly graphic) workstations and workstation operating systems and their software are differentiated from (mostly console- based) servers and server operating systems with associated software. In the meantime, however, both expressions - at least colloquially and in connection with hardware - are practically synonymous.
Server hosts usually run permanently. Therefore, preferably in the respective computers components are used which are designed for continuous operation, for example, SAS - disks instead of SATA hard disks. RAIDs are standard, several main processors and redundant power supplies are common.
In principle, hosts can be operated by servers on any type of computer. In data centers , such computers are usually built in the 19 "format (19" wide, 1.75 "high) so that they fit into a standardized 19" rack in order to make optimal use of the available space. Other forms are the blade servers .
The concept of virtual hosts has been in use in the mainframe area for a long time, with IBM pioneering this in the 1960s. On PC based, emulated virtual machines were first offered in the 1990s, in the PC range was here Connectix from 1997 and VMware from 1999 pioneer. Only since then has PC hardware been powerful enough to be able to map several virtual machines on one computer.
Virtual hosts are used when different services are to be offered by a single machine, each of which requires its own operating system environment (cf. dedicated host ) .
Virtual hosts allow a quick and easy changeover to new, more powerful hardware or the relocation of individual virtual hosts with the servers running on them to another machine. [Receipt?]
Virtual hosts can be divided into two groups: virtual hosts based on operating systems and virtual hosts based on emulation.
A host operating system ( English host ) houses several guest operating system environments (English guest ), which are isolated from each other and are only allowed to access the host's hardware via the host operating system.
Operating system-based virtualization is available at different levels:
- Extended chroot environment of the host system. Direct access to the system hardware is not possible. Example: BSD jails (see below) , LXC and Linux-VServer .
- Guest systems use the same operating system as the host and access the hardware via drivers of the host system. Example: Virtuozzo
- The guest systems are complete operating systems with their own (or shared, but protected) kernel, their own drivers and their own configuration. Example: UML , Xen
Emulation or virtualization
The host system emulates all system calls on the hardware level or emulates a complete hardware architecture (including CPU, memory access, etc.).
From the host's point of view, a classic emulator is usually a completely normal program. B. possible to test software for Palm handhelds on PCs, to use old C64 software, or to run a complete x86 Windows system on a PowerPC Apple or HP Unix computer.
If you "only" want to run other operating systems (which are in principle suitable for the same hardware architecture) or instances on a physical machine, virtualization is an option as opposed to emulation . Examples: KVM , Windows Virtual PC , VMware .
The boundaries between virtualization and emulation are fluid, especially since "mainstream" processors have also been supplemented by virtualization aids since around 2010 (e.g. Intel VT and AMD-V ) or various solutions for the guest system's program code before execution (in part) for the Convert suitable code to host PC ( just-in-time compilation ).
A distinction can be made between two forms:
- IP-based virtual hosts require that multiple IP addresses be assigned to the host's network interface . In order to provide the correct data in response to a request, the server evaluates it according to the IP address that is being addressed.
- Name-based virtual hosts require that multiple hostnames be assigned to the host's IP address in the Domain Name System . In order to provide the correct data in response to a request, the server evaluates your host header .
For example, requests to the hosts de.wikipedia.org and en.wikipedia.org are answered by the same host with different content.
A single HTTP server can run on the host for all virtual hosts or a separate HTTP server with its own configuration for each virtual host.
As a dedicated host ( borrowed from English. Dedicated host ), a host refers to the (Engl. Only for a task dedicated service ) off (or literally This [task] dedicated or allotted ) is or has a customer (the dedicated customer assigned) is.
Assigned to an activity
- operation area
- Operating systems that do not run stably with multiple services.
- Services that cannot be operated jointly on one host.
Examples: an old, a current and a development version of a web server that have different system requirements, or a web server that contains the website of an individual customer, which because of its size, its visitor frequency or because of technical features (e.g. use of a content Management system ) cannot be located on a shared, shared server with other websites.
Assigned to a customer
In the web hosting industry and geography, the term is dedicated hosts frequently used for offers renting ( English dedicated to customer , so literally as the customer paid ). The Internet service provider rents out a computer including parking space, air conditioning and power supply or a virtual machine . Some providers misleadingly refer to dedicated hosts on which the customer himself uses the root account as “root servers”.
Dedicated hosts are used when:
- more performance is required than a shared server or a virtual machine offers
- the security should not be compromised by other uses of the host
- desired software cannot be operated together with existing software on a host
- the customer wants to make it more difficult for the provider to view his data
- the host requires special security measures
- the customer wants to use software that is not supported by the provider
- the customer wants comprehensive access rights, which excludes access for others
As a managed host , managed dedicated host or misleading managed servers dedicated hosts the operating system and are referred to, software (server) is monitored by the provider and updates. As virtual machines, they are usually made available (rented) by the provider; as computers, they are rented, leased or bought by the customer .
The managed host offers on the market often include extended services such as telephone support, boot service and simple repairs. This is intended to combine the advantages of a dedicated host with those of a web hosting offer, in that administrative tasks are relieved of the customer, high availability of the hardware is guaranteed and an individual configuration of the server on this host is still possible.
The scope of services of managed hosts often includes:
Operating system updates, software updates, application installation, extended configuration options, telephone support, extended technical support, firewall services, security scans / audits, anti-spam / virus protection, backup services, server monitoring and recovery, database Management, control panel software.
- Linux-VServer , German Linux-VServer-HowTo
- FreeBSD Jail , official documentation
- Xen virtual machine monitor
- Microsoft Virtual Server
- sysjail - supports OpenBSD, NetBSD and MirOS and is based on FreeBSD jail
- Apache documentation on virtual hosts
- The historical-technical dimension: The networking of the world - Jochen Koubek at the HU Berlin , on February 10, 2003
- Detlef Borchers: 40 years ago: the perfect computer. In: Heise online . April 7, 2004 . Retrieved January 15, 2017.
- Ralph Hülsenbusch: IBM celebrates 50 years of medium-sized data technology. In: Heise online . October 6, 2009 . Retrieved January 15, 2017.
- IBM CP-40 in the English language Wikipedia
- VMware Milestones. (No longer available online.) Archived from the original on April 16, 2011 ; accessed on January 3, 2011 .
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