The host (English for host, host, organizer ) a mounted in a computer network computer system is called with the associated operating system, serving the clients or home server (software).
Historically, the term initially host a multi-user computer with software that provides computing services for computer terminals. Having conquered the everyday computer networks in the 1980s, the term was also used for device connected to a computer network computers that provide services for mostly smaller or less powerful systems.
In addition to complex operating systems of computers and specialized systems of network devices such as routers and print servers hosts can be. For example, any system that can obtain its network configuration through the Dynamic Host Configuration Protocol (DHCP ) client a DHCP server.
- 4.1 One of activity assigned (dedicated to service )
- 4.2 A customer assigned (dedicated to customer )
History of host - concept
The term host is used at an early stage in the computer in the 1960s in connection with mainframes or mid-range systems and there usual time-sharing or multi-user operating systems. These systems are highly structured and essentially consist of a central processing unit, which is also known as the host and all the "intelligence" of houses, and the "dumb" terminals that are used only as a user terminal in the workplace and in practice only for input and output of data are used. The frequently used as a synonym expression server is more recent and comes from the field of personal computers and operating systems such as Banyan Vines, Mac OS, NetWare, or Unix. As the networking of these computers class virtually anywhere found its way at the end of the 1980s, they sought to distinguish it from the existing host - based architectures, an alternative designation and established this, the term server. The architecture on the basis of personal computers typically have no "intelligent" hosts - in contrast to "dumb" terminals, in this case, each system is "intelligence" provided with more or less. In this context, computer systems ( hardware and software), which is essentially other systems provide services (see: "Server (software) " ), called a server. In the Unix environment, differentiation at this time is clear, here are (usually graphical ) workstations and workstation operating systems and their software (mostly console -based ) distinction servers and server operating systems and associated software. However, by now are both expressions - at least colloquially and in connection with hardware - practically synonymous.
Hosts of servers running usually permanent. Therefore, in the appropriate computers preferred components are used, which are designed for continuous operation, such as SAS drives instead of SATA drives. RAIDs are standard, a plurality of main processors and redundant power supplies distributed.
In principle hosts of servers on any type of computer can be operated. In data centers such computers are usually in the 19 "format (19 inches wide, 1.75 inches high) built to allow them into a standard 19 " rack fit to make optimum use of the available space. Other types are the so-called blade server.
The concept of virtual hosts has long been on mainframe computers in use, pioneering IBM was here in the 1960s. Based on PC emulated virtual machines were first offered in the 1990s, was a pioneer here from 1999 Connectix and VMware. It is only since that time PC hardware powerful enough to map on a computer multiple virtual machines.
Virtual hosts are used when different services to be offered by a single machine, each with its own operating system environment require (see Dedicated Host).
Virtual hosts allow a quick and painless transition to new, more powerful hardware or the displacement of individual virtual hosts running on the servers to another machine. [ Evidence ?]
Virtual hosts can be divided into two groups: virtual hosts on the basis of operating systems and virtual hosts based on emulation.
Virtual hosts on the basis of operating systems
A host operating system (English host) hosts several guest operating system environments (English guest) that are shielded against each other and allowed to access the hardware of the host only through the host operating system.
Virtualization at the operating system base there are at different levels:
- Advanced chroot environment of the host system. Direct access to the system hardware is not possible. Example: BSD jails (see below), and LXC Linux - VServer.
- Guest systems use the same operating system as the host and grab the drivers of the host system on the hardware. Example: Virtuozzo
- The guest systems are complete with their own operating systems (or common but protected ) Kernel, drivers and own your own configuration. Example: UML, Xen
Virtual hosts on the basis of emulation or virtualization
The host system emulates all system calls at the hardware level or emulates a complete hardware architecture (including CPU, memory accesses, etc ).
A classic emulator from the host perspective are often a normal program, it is for example possible to test on PC software for Palm handhelds to use old C64 software, or a full x86 Windows system on a PowerPC Apple - to run or HP- Unix machine.
To be the " only " other operating systems or instances on a physical machine (which are generally suitable for the same hardware architecture) to run, provides, in contrast to emulation virtualization on. Examples: KVM, Windows Virtual PC, VMware.
The boundaries between virtualization and emulation are fluid, especially since currently also " mainstream " processors are supplemented with virtualization support ( eg Intel VT and AMD- V) or various solutions program code of the host system prior to execution ( in part) in the host reshape PC suitable code.
The configuration of Apache HTTP server contains a virtual host directive that allows multiple separate sites on a single host.
Two forms can be distinguished:
- IP - based virtual hosts require that the network interface of the host multiple IP addresses are assigned. To provide the correct data to a request, the server evaluates it for the IP address that is addressed.
- Name-based virtual hosts require that the IP address of the host in the domain name system more host names can be assigned. In order to provide the right data to a request, the server evaluates their host header.
On the host, a single HTTP server for all virtual hosts or for each virtual host has its own HTTP server run on a stand-alone configuration.
More articles on the Virtual Hosts
External links about Virtual Hosts
- 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 Virtual Host documentation
As a dedicated host (English dedicated host) is a designated host, which is parked for a task (dedicated service) or just assigned to a customer is (dedicated customer).
One activity assigned (dedicated to service )
Instead of having multiple servers running on a host, each its own dedicated host is dedicated. As hosts physical and virtual hosts are used.
- Operating systems that can not run stable with multiple services.
- Services that can not coexist on a host.
Examples: an old, a current and a development version of a web server that have different system requirements, or a Web server, which includes the site of an individual customer, because of their size, number of visitors or technical features (eg use of a content - management system ) may lie not in conjunction with other Web sites on a common, shared server ( shared server ).
A customer assigned (dedicated to customer )
In the web hosting industry, the concept of dedicated hosts is often used for rental offers. Here, the Internet service provider rents a computer including parking space, air conditioning and power supply or a virtual machine. Some vendors refer to dedicated hosts running the client itself uses the root account, misnamed " root servers ".
Dedicated hosts to be used if:
- More power is required as a shared server, or a virtual machine provides
- Safety should not be compromised by other uses of the host
- Desired software can not be run in conjunction with existing on a host
- The customer wants the seller complicate the insight into its data
- The host requires special security measures
- The customer wants to use a software that is not supported by the provider
- The customer comprehensive access rights wishes, which precludes access to other
As a managed host, managed dedicated host or misleading Managed dedicated server hosts are known, their operating system and software (server ) is monitored and updated by the provider. As virtual machines they are made available generally by the provider ( rented), as a computer they are rented by the customer, leased or purchased.
In the market have managed host packages often include advanced services such as telephone support, boat service and repairs simple. This will allow a web hosting offer combine the advantages of a dedicated hosts by the customer administrative tasks are taken, high availability of the hardware is guaranteed and yet an individual configuration of the server on this host is possible.
Often included in the scope of managed hosts:
Operating system updates, software updates, application installation, advanced configuration options, phone support, advanced technical support, firewall services, security scans / audits, Anti-Spam/Virus-Schutz, backup services, server monitoring and recovery, database management, control panel software.