Types Of Computer

According to size

Microcomputers:

A microcomputer is a computer with a microprocessor as its central processing unit. They are physically small compared to mainframe and minicomputers. Many microcomputers (when equipped with a keyboard and screen for input and output) are also personal computers (in the generic sense)

This type of computers include systems that are for general purpose and for business needs. They are usually called PC’s (Personal Computers) based on the microprocessor. Examples are desktop computers, laptop, notebook etc

Monitors, keyboards and other devices for input and output may be integrated or separate. Computer memory in the form of RAM, and at least one other less volatile, memory storage device are usually combined with the CPU on a system bus in a single unit. Other devices that make up a complete microcomputer system include, batteries, a power supply unit, a keyboard and various input/output devices used to convey information to and from a human operator (printers, monitors, human interface devices) Microcomputers are designed to serve only a single user at a time, although they can often be modified with software or hardware to concurrently serve more than one user. Microcomputers fit well on or under desks or tables, so that they are within easy access of the user. Bigger computers like minicomputers, mainframes, and supercomputers take up large cabinets or even a dedicated room.

A microcomputer comes equipped with at least one type of data storage, usually RAM. Although some microcomputers (particularly early 8-bit home micros) perform tasks using RAM alone, some form of secondary storage is normally desirable. In the early days of home micros, this was often a data cassette deck (in many cases as an external unit). Later, secondary storage (particularly in the form of floppy disk and hard disk drives) were built in to the microcomputer case itself.



Server:

Basically server runs a network of computers and optimizes services to the other computers interlinked with that server. Example File Server, Print Server, Chat Server etc.
A server computer is a computer, or series of computers, that link other computers or electronic devices together. They often provide essential services across a network, either to private users inside a large organization or to public users via the internet. For example, when you enter a query in a search engine, the query is sent from your computer over the internet to the servers that store all the relevant web pages. The results are sent back by the server to your computer.

Many servers have dedicated functionality such as web servers, print servers, and database servers. Enterprise servers are servers that are used in a business context.

The server is used quite broadly in information technology. Despite the many Server branded products available (such as Server editions of Hardware, Software and/or Operating Systems), in theory any computerised process that shares a resource to one or more client processes is a Server. To illustrate this, take the common example of File Sharing. While the existence of files on a machine does not classify it as a server, the mechanism which shares these files to clients by the operating system is the Server.

Similarly, consider a web server application (such as the multiplatform "Apache HTTP Server"). This web server software can be run on any capable computer. For example, while a laptop or Personal Computer is not typically known as a server, they can in these situations fulfil the role of one, and hence be labelled as one. It is in this case that the machine's purpose as a web server classifies it in general as a Server.

In the hardware sense, the word server typically designates computer models intended for running software applications under the heavy demand of a network environment. In this client–server configuration one or more machines, either a computer or a computer appliance, share information with each other with one acting as a host for the other.

While nearly any personal computer is capable of acting as a network server, a dedicated server will contain features making it more suitable for production environments. These features may include a faster CPU, increased high-performance RAM, and typically more than one large hard drive. More obvious distinctions include marked redundancy in power supplies, network connections, and even the servers themselves.

Between the 1990s and 2000s an increase in the use of dedicated hardware saw the advent of self-contained server appliances. One well-known product is the Google Search Appliance, a unit which combines hardware and software in an out-of-the-box packaging. Simpler examples of such appliances include switches, routers, gateways, and print server, all of which are available in a near plug-and-play configuration.

Modern operating systems such as Microsoft Windows or Linux distributions rightfully seem to be designed with a client–server architecture in mind. These OSes attempt to abstract hardware, allowing a wide variety of software to work with components of the computer. In a sense, the operating system can be seen as serving hardware to the software, which in all but low-level programming languages must interact using an API.

WorkStation:

This device is a very powerful microcomputer. It is designated with high speed, large storage capacity and additional memory. Workstation hosts those application that needs powerful processing like complex scientific calculations graphics related tasks and game development.

A workstation is a high-end microcomputer designed for technical or scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area network and run multi-user operating systems. The term workstation has also been used to refer to a mainframe computer terminal or a PC connected to a network.



Historically, workstations had offered higher performance than personal computers, especially with respect to CPU and graphics, memory capacity and multitasking capability. They are optimized for the visualization and manipulation of different types of complex data such as 3D mechanical design, engineering simulation (e.g. computational fluid dynamics), animation and rendering of images, and mathematical plots. Consoles consist of a high resolution display, a keyboard and a mouse at a minimum, but also offer multiple displays, graphics tablets, 3D mice (devices for manipulating and navigating 3D objects and scenes), etc. Workstations are the first segment of the computer market to present advanced accessories and collaboration tools.


Presently, the workstation market is highly commoditized and is dominated by large PC vendors, such as Dell and HP, selling Microsoft Windows/Linux running on Intel Xeon/AMD Opteron. Alternative UNIX based platforms are provided by Apple Inc., Sun Microsystems, and SGI.



Mainframe:


This machine is used by companies or business where thousands of instructions executes simultaneously and are done in a limited time. Workers are connected with each other and working on the same data. These machines are very huge and are very rarely used.

Mainframes (often colloquially referred to as Big Iron[1]) are powerful computers used mainly by large organizations for critical applications, typically bulk data processing such as census, industry and consumer statistics, enterprise resource planning, and financial transaction processing.



The term originally referred to the large cabinets that housed the central processing unit and main memory of early computers.[2][3] Later the term was used to distinguish high-end commercial machines from less powerful units.


Most large-scale computer system architectures were firmly established in the 1960s and most large computers were based on architecture established during that era up until the advent of Web servers in the 1990s. (The first Web server running anywhere outside Switzerland ran on an IBM mainframe at Stanford University as early as 1991. See History of the World Wide Web for details.)


There were several minicomputer operating systems and architectures that arose in the 1970s and 1980s, but minicomputers are generally not considered mainframes. (UNIX arose as a minicomputer operating system; Unix has scaled up over the years to acquire some mainframe characteristics.)


Many defining characteristics of "mainframe" were established in the 1960s, but those characteristics continue to expand and evolve to the present day.

Modern mainframe computers have abilities not so much defined by their single task computational speed (usually defined as MIPS — Millions of Instructions Per Second) as by their redundant internal engineering and resulting high reliability and security, extensive input-output facilities, strict backward compatibility with older software, and high utilization rates to support massive throughput. These machines often run for years without interruption, with repairs and hardware upgrades taking place during normal operation.



Software upgrades are only non-disruptive when using facilities such as IBM's z/OS and Parallel Sysplex, with workload sharing so one system can take over another's application while it is being refreshed. More recently, there are several IBM mainframe installations that have delivered over a decade of continuous business service as of 2007, with hardware upgrades not interrupting service.[citation needed] Mainframes are defined by high availability, one of the main reasons for their longevity, because they are typically used in applications where downtime would be costly or catastrophic. The term Reliability, Availability and Serviceability (RAS) is a defining characteristic of mainframe computers. Proper planning (and implementation) is required to exploit these features.


In the 1960s, most mainframes had no interactive interface. They accepted sets of punched cards, paper tape, and/or magnetic tape and operated solely in batch mode to support back office functions, such as customer billing. Teletype devices were also common, at least for system operators. By the early 1970s, many mainframes acquired interactive user interfaces and operated as timesharing computers, supporting hundreds of users simultaneously along with batch processing. Users gained access through specialized terminals or, later, from personal computers equipped with terminal emulation software. Many mainframes supported graphical terminals (and terminal emulation) but not graphical user interfaces by the 1980s, but end user computing was largely obsoleted in the 1990s by the personal computer. Nowadays most mainframes have partially or entirely phased out classic terminal access for end-users in favor of Web user interfaces. Developers and operational staff typically continue to use terminals or terminal emulators.[citation needed]


Historically, mainframes acquired their name in part because of their substantial size, and because of requirements for specialized heating, ventilation, and air conditioning (HVAC), and electrical power. Those requirements ended by the mid-1990s with CMOS mainframe designs replacing the older bipolar technology. IBM claims its newer mainframes can reduce data center energy costs for power and cooling, and that they can reduce physical space requirements compared to server farms.



Supercomputers:


These computers are very powerful from all other computers in terms of strength and expense. Usually it is a very large computer but some time some other big computers work parallel to do a heavy task. Supercomputers are doing the great job of tasks that others computers don’t have the capability to do so. It performs massive amount of scientific calculations, weather forecasting, critical decryption of data, testing for engineering tasks.

A supercomputer is a computer that is at the frontline of current processing capacity, particularly speed of calculation. Supercomputers were introduced in the 1960s and were designed primarily by Seymour Cray at Control Data Corporation (CDC), which led the market into the 1970s until Cray left to form his own company, Cray Research. He then took over the supercomputer market with his new designs, holding the top spot in supercomputing for five years (1985–1990). In the 1980s a large number of smaller competitors entered the market, in parallel to the creation of the minicomputer market a decade earlier, but many of these disappeared in the mid-1990s "supercomputer market crash".



Today, supercomputers are typically one-of-a-kind custom designs produced by "traditional" companies such as Cray, IBM and Hewlett-Packard, who had purchased many of the 1980s companies to gain their experience. As of May 2010[update], the Cray Jaguar is the fastest supercomputer in the world.

The term supercomputer itself is rather fluid, and today's supercomputer tends to become tomorrow's ordinary computer. CDC's early machines were simply very fast scalar processors, some ten times the speed of the fastest machines offered by other companies. In the 1970s most supercomputers were dedicated to running a vector processor, and many of the newer players developed their own such processors at a lower price to enter the market. The early and mid-1980s saw machines with a modest number of vector processors working in parallel to become the standard. Typical numbers of processors were in the range of four to sixteen. In the later 1980s and 1990s, attention turned from vector processors to massive parallel processing systems with thousands of "ordinary" CPUs, some being off the shelf units and others being custom designs. Today, parallel designs are based on "off the shelf" server-class microprocessors, such as the PowerPC, Opteron, or Xeon, and coprocessors like NVIDIA Tesla GPGPUs, AMD GPUs, IBM Cell, FPGAs. Most modern supercomputers are now highly-tuned computer clusters using commodity processors combined with custom interconnects.


Supercomputers are used for highly calculation-intensive tasks such as problems involving quantum physics, weather forecasting, climate research, molecular modeling (computing the structures and properties of chemical compounds, biological macromolecules, polymers, and crystals), physical simulations (such as simulation of airplanes in wind tunnels, simulation of the detonation of nuclear weapons, and research into nuclear fusion). A particular class of problems, known as Grand Challenge problems, are problems whose full solution requires semi-infinite computing resources.

Supercomputers using custom CPUs traditionally gained their speed over conventional computers through the use of innovative designs that allow them to perform many tasks in parallel, as well as complex detail engineering. They tend to be specialized for certain types of computation, usually numerical calculations, and perform poorly at more general computing tasks. Their memory hierarchy is very carefully designed to ensure the processor is kept fed with data and instructions at all times — in fact, much of the performance difference between slower computers and supercomputers is due to the memory hierarchy. Their I/O systems tend to be designed to support high bandwidth, with latency less of an issue, because supercomputers are not used for transaction processing.


As with all highly parallel systems, Amdahl's law applies, and supercomputer designs devote great effort to eliminating software serialization, and using hardware to address the remaining bottlenecks.