Classification of Computers Computer systems used for business purposes can be divided in to three classes: Microcomputers, Minicomputers and Mainframe computers. Though these divisions are loosely based on the size of the computer systems, there are no hard and fast rules for deciding exactly where one category ends and the next begin. Hence the largest minicomputer systems are often larger than the smallest mainframe computers. The “size” of a computer system is dependent on the size of a computer’s hardware configuration, the nature of its applications, and the complexity of its system software. This helps us to classify a system as a microcomputer, minicomputer or mainframe. Irrespective of size, all computers consist of two basic types of components. Those are processors and input/output (I/O) devices. The processor consists of three parts: the Central Processing Unit, or CPU, main storage and device controllers. The CPU executes instructions, main storage stores instructions and data processed by the CPU and device controllers let the CPU and main storage connect to I/O devices. Note: Though all computer systems consist of three basic components, the way those components are combined for a particular computer system varies depending on the system’s requirements. Microcomputer or Personal Computer Microcomputer is primarily intended for stand-alone use by an individual. Microcomputers are small, single-user systems which provide a simple processor and just a few input/output devices. This system consists of a processor with 2 or 4 GB of main storage, a keyboard, a display monitor, a printer, and a diskette drive with a capacity of 4GB and a 500 GB of hard disk. Different models are available, such as Desktop, Notebook, Laptop, Hand-held, Palmtop and PDA. Minicomputer Unlike microcomputers, most of the minicomputers provide more than one terminal so that several users can use the system at a time. Such systems are referred to as “multi- user systems”. The Mini computer – Mini computers like the mainframe computers are used by business organization. The difference being that it can support the simultaneous working of up to 100 users and is usually maintained in business organizations for the maintenance of accounts and finances. Super Computer Supercomputer is a broad term for one of the fastest computers currently available. Supercomputers are very expensive and are employed for specialized applications that require immense amounts of mathematical calculations (number crunching). For example, weather forecasting requires a supercomputer. Other uses of supercomputers scientific simulations, (animated) graphics, fluid dynamic calculations, nuclear energy research, electronic design, and analysis of geological data (e.g. in petrochemical prospecting). Perhaps the best known supercomputer manufacturer is Cray Research Mainframe Computer A mainframe computer consists of the same basic types but has more I/O devices and larger storage capacities. Mainframe was a term originally referring to the cabinet containing the central processor unit or "main frame" of a room-filling Stone Age batch machine. After the emergence of smaller "minicomputer" designs in the early 1970s, the traditional big iron machines were described as "mainframe computers" and eventually just as mainframes. Nowadays a Mainframe is a very large and expensive computer capable of supporting hundreds, or even thousands, of users simultaneously. The chief difference between a supercomputer and a mainframe is that a supercomputer channels all its power into executing a few programs as fast as possible, whereas a mainframe uses its power to execute many programs concurrently. In some ways, mainframes are more powerful than supercomputers because they support more simultaneous programs. But supercomputers can execute a single program faster than a mainframe. Note In the past decade, the distinction between large minicomputers and small mainframes has blurred, however, as has the distinction between small minicomputers and workstations. But in general, a minicomputer is a multiprocessing system capable of supporting from up to 200 users simultaneously. As the size of computers has diminished while the power has increased, the term mainframe has fallen out of use in favor of enterprise server. You'll still hear the term used, particularly in large companies to describe the huge machines processing millions of transactions every day Today Mainframe almost always refers to IBM’s zSeries computers. And that’s what this book is all about. From now on when we talk about Mainframes, we’re talking about the zSeries machines. What is Server Technology A “server” is simply a computer, any computer that provides “services” to other computers. If you computer can share its files, it’s a file server. If you turn iTunes music sharing on, your computer becomes a music server. If you have a shared printer, your computer has become a print server. A server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients". The clients either run on the same computer or connect through the network. Depending on the computing service that it offers it could be a database server, file server, mail server, print server, web server, or other. For example, when you enter a query in Google, the query is sent from your computer over the internet to the Google servers that store all the relevant web pages. The results are sent back by the server to your computer. We can find the following types of servers around the world: Database server - Provides database services to other computer programs or computers Web server - Server that HTTP clients connect to in order to send commands and receive responses along with data contents Standalone server - Emulator for client–server (web-based) programs Proxy server - Acts as an intermediary for requests from clients seeking resources from other servers And so on… Do we need a server? Why? “Do we need a server?” is a common question. The real hidden question is “What does a server do for my organization, and do we need something that does that?” Servers can actually do a lot of different things, which is why it’s sometimes difficult to decide. However, for the Small to Medium-sized organization, a server typically “serves” in any or all of the following roles: Central file storage Backups Email Network printer sharing Firewall Remote connection Security for user account and file access Flexibility and expandability for new functions in the future So … In this globalization era, most of the business runs with datum from different states, countries and continents. Undoubtedly, computers handshake across regions and thereby Servers become a standard icon for a Business or Organization. Servers often run for long periods without interruption and availability must often be very high, making hardware reliability and durability extremely important. Those are ideally very fault tolerant and use specialized hardware with low failure rates in order to maximize uptime, for even a short-term failure can cost more than purchasing and installing the system. Mainframe: Is It a Server? Mainframes are Servers, the way we have client-server computing today, but they are not called servers because the "clients" of a mainframe system are usually terminals. These are dumb terminals, which mean all the applications they run on big system. Nothing is being served to the client...all the work is done on the big machine. A Mainframe is usually dedicated for one purpose like a Bank or Corporate. Generally Mainframe machines acts as a servers (but they are not called as servers). You throw tasks to the Mainframe machine, and the mainframe performs the processing, and stores the result. Many users throw requests to the Mainframe machine concurrently. Thus, as a mainframe operator, generally you would not be present physically near the machine, you operate it remotely. you have a keyboard and monitor connected to your Mainframe server. There would be thousands of terminals connected to a mainframe server and many users can perform their tasks on the mainframe server concurrently. You might sit in the work-office of your company on a terminal and perform data-processing on the Mainframes server located somewhere else. So different types of computers or technology acts as a Server(But not a server). So a Personal computer can be a server, Mini computer can be a server, Mainframe computer can be a server and so on. But these differ on some factor and especially on RAS. RAS (Reliability, Availability and Serviceability) decides the strength of any Servers. Reliability, Availability and Serviceability (RAS) Reliability, Availability and Serviceability (RAS) is a set of related attributes that must be considered when designing, manufacturing, purchasing or using a computer product or component. The term was first used by IBM to define specifications mainframes and originally applied only to hardware. Today RAS is relevant to software as well and can be applied to networks, application programs, operating systems (OS), personal computers (PCs) and supercomputers. But especially Servers. Reliability - Ability of a computer-related hardware or software component to consistently perform according to its specifications. In a simple form, it is “not only free from technical errors but also avoid such errors once it arrives”. A reliable system Helps itself to avoid and detect faults. Does not silently continue and deliver results with corrupted data instead it corrects or else stops and reports the corruption. Availability - The ratio of time a system or component is functional to the total time it is required or expected to function. It may be reported as minutes or hours of downtime per year. This can be expressed as a direct proportion (for example, 9/10 or 0.9) or as a percentage (for example, 90%). A system with high availability This allows the system to stay operational even when faults do occur.