The term IT-architecture is named frequently the conceptional structure of the information systems of an organization/an enterprise. A small overview of (partially already historical) architectures describes that more near.

Conceptional differences of different computer worlds

Host systems

• Description in terms of catchwords:
  • efficient central computer (large computer, host system), attached to it over narrow-band lines "stupid "terminals, frequently transaction-oriented enterprise.
  • Example: Bookkeeping system of banks, world-wide Ticketing of an airline: Central system with many CCUs, much memory, large Plattensystemen.

• Advantages:
  • System sovereignty central in the operating IT-department
  • tightens organization
  • Enterprise i.d.R. very efficiently
  • no multiple developments
  • high availability because of matured technology and central responsibility
  • narrow-band range need
  • simple maintenance concept with terminals distributed world-wide

• Disadvantages:
  • Dependence of the user ranges (bottleneck IT-center)
  • Strangle creativity
  • no modern Graphical user interface (GUI) available, only indication-oriented sceen contents
  • high training course expenditure for use of indication-oriented applications

To the range: The only narrow-band range requirement is justified in history: Lines were expensive, therefore range should be saved. Consequence: kryptische operation, which users had themselves to notice many abbreviations for commands, auxiliary information of the system were very economically.

To the terminal hardware: With the arising of PCs this frequently with an emulation software/- hardware were equipped, which they represented in relation to the host system as a terminal. Thus increasingly the obligation was void to use terminals the specialized (and thus usually expensive).

Personal computer (PC)

local opposite to the central host system: PC.

• Advantages:
  • Chance to the user friendly GUI
  • Operating know-how depending upon used operating system already there (small training course expenditure)
  • Standard hardware very favorably

• Disadvantages:
  • Trend to Parallelentwicklungen in individual departments
  • Frequently no documentation provides
  • Frequently no Backupkonzept
  • no 24h-Betrieb and/or coworker-dependently
  • no solution for world-wide uniform data and applications
  • Problem: complex, with difficulty adminstrierbar, some BS very imperfectly, various direct access of the user

Client/server

PC with access to servers. In principle no technical difference must exist, however performantere/more reliable (and more extensive) hardware in the server is usually used between Client and server hardware.

Exact development however essentially depends on the planned targeted application.

• Advantage:
  • Distribution of functionality: GUI on Client, data and application on servers. Places one mix from the two aforementioned forms and is in particular for geographically distributed users and small Lokationen, like e.g. tax preparation for national addresses, meaningful.
  • Centralization of certain ranges feasiblly (responsibility for system operation, data security etc.), at the same time however decentralized flexibility possible.
• Disadvantages:
  • If necessary high complexity of the applications (PC+Server), high range need
  • high would support-wind up zentral+dezentral
• Technology:
  • much RAM
  • very much quick plates (- subsystems, SAN)
  • LAN /WAN binding wide-band
  • Everything redundantly available: Power pack, CCUs, plates, hot swap possibility

Terminal server

Connects advantages from host and PC range:

• Advantages:
  • Central administration
  • User rights very far limitable
  • Thin Clients possible, thus very simple decentralized maintenance

• Disadvantage:
  • Central system must have power reserves and be loss-poor.

• Technology:
  • The data communication takes place by remote Desktop Protocol

Summary

Host systems have quite still their authorization in some special cases, which large mass of the IT-systems in the enterprises today however on basis of Client/server systems or - with at present increasing tendency - terminal server concepts realized. Newer developments within the host range try to position large computers than server replacement in certain cases (e.g. particularly high reliability, very high performance requirements). In these cases the large computer operating system emulates a multiplicity with the help of an application "more virtually "servers, which run apparently independently in each case with own operating system and own applications.

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