A Computer is a programmable machine.
The two principal characteristics of a computer are:
- It responds to a specific set of instructions in a well-defined manner.
- It can execute a prerecorded list of instructions (a program ).
Modern computers are electronic and digital.The actual machinery wires, transistors, and circuits is called hardware. the instructions and data are called software.
All general-purpose computers require the following hardware components:
Memory: Enables a computer to store, at least temporarily, data and programs.
Mass storage device: Allows a computer to permanently retain large amounts of data. Common mass storage devices include disk drives and tape drives.
Input device: Usually a keyboard and mouse are the input device through which data and instructions enter a computer.
Output device: A display screen, printer, or other device that lets you see what the computer has accomplished.
Central processing unit (CPU): The heart of the computer, this is the component that actually executes instructions.
In addition to these components, many others make it possible for the basic components to work together efficiently.For example, every computer requires a bus that transmits data from one part of the computer to another.
Computers can be generally classified by size and power as follows, though there is considerable overlap:
Personal computer: A small, single-user computer based on a microprocessor.In addition to the microprocessor, a personal computer has a keyboard for entering data, a monitor for displaying information, and a storage device for saving data.
Working station: A powerful, single-user computer. A workstation is like a personal computer, but it has a more powerful microprocessor and a higher quality monitor.
Minicomputer: A multi-user computer capable of supporting from 10 to hundreds of users simultaneously.
Mainframe: A powerful multi-user computer capable of supporting many hundreds or thousands of users simultaneously.
Supercomputer: An extremely fast computer that can perform hundreds of millions of instructions per second.
1) A type of computer used for engineering applications (CAD/CAM), desktop publishing, software development, and other types of applications that require a moderate amount of computing power and relatively high quality graphics
- Workstations generally come with a large, high- resolution graphics screen, at least 64 MB (mega bytes) of RAM, built-in network support, and a graphical user interface.
- Most workstations also have a mass storage device such as a disk drive, but a special type of workstation, called a diskless workstation, comes without a disk drive.
- The most common operating systems for workstations are UNIX and Windows NT.
- In terms of computing power, workstations lie between personal computers and minicomputers, although the line is fuzzy on both ends.
- High-end personal computers are equivalent to low-end workstations. And highend workstations are equivalent to minicomputers.
- Like personal computers, most workstations are single-user computers. However, workstations are typically linked together to form a local-area network, although they can also be used as stand-alone systems.
2) In networking, workstation refers to any computer connected to a local-area network. It could be a workstation or a personal computer.
- A very large and expensive computer capable of supporting hundreds, or even thousands, of users simultaneously. In the hierarchy that starts with a simple microprocessors (in watches, for example) at the bottom and moves to supercomputer at the top, mainframes are just below supercomputers.
- 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. The distinction between small mainframes and minicomputers is vague, depending really on how the manufacturer wants to market its machines.
- The term microcomputer is generally synonymous withpersonal computer, or a computer that depends on a microprocessor.
- Microcomputers are designed to be used by individuals, whether in the form of PCs, workstations or notebook computers.
- A microcomputer contains a CPU on a microchip (the microprocessor), a memory system (typically ROM and RAM), a bus system and I/O ports, typically housed in a motherboard.
- A silicon chip that contains a CPU. In the world of personal computers, the terms microprocessor and CPU are used interchangeably.
- A microprocessor (sometimes abbreviated µP) is a digital electronic component with miniaturized transistors on a single semiconductor integrated circuit (IC).
- One or more microprocessors typically serve as a central processing unit (CPU) in a computer system or handheld device.
- Microprocessors made possible the advent of the microcomputer.
- At the heart of all personal computers and most working stations sits a microprocessor.
- Microprocessors also control the logic of almost all digital devices, from clock radios to fuel-injection systems for automobiles.
Three basic characteristics differentiate microprocessors:
Instruction set: The set of instructions that the microprocessor can execute.
Bandwidth: The number of bits processed in a single instruction.
Clock speed: Given in megahertz (MHz), the clock speed determines how many instructions per second the processor can execute.
- In both cases, the higher the value, the more powerful the CPU. For example, a 32 bit microprocessor that runs at 50MHz is more powerful than a 16-bit microprocessor that runs at 25MHz.
- In addition to bandwidth and clock speed, microprocessors are classified as being either RISC (reduced instruction set computer) or CISC (complex instruction set computer).
Supercomputer: A supercomputer is a computer that performs at or near the currently highest operational rate for computers. A supercomputer is typically used for scientific and engineering applications that must handle very large databases or do a great amount of computation (or both).
At any given time, there are usually a few well-publicized supercomputers that operate at the very latest and always incredible speeds. The term is also sometimes applied to far slower (but still impressively fast) computers.
Most supercomputers are really multiple computers that perform parallel processing.
In general, there are two parallel processing approaches: symmetric multiprocessing (SMP) and massively parallel processing (MPP).
Microcontroller: A highly integrated chip that contains all the components comprising a controller. Typically this includes a CPU, RAM, some form of ROM, I/O ports, and timers. Unlike a general-purpose computer, which also includes all of these components, a microcontroller is designed for a very specific task – to control a articular system.
A microcontroller differs from a microprocessor, which is a general-purpose chip that is used to create a multi-function computer or device and requires multiple chips to handle various tasks.
A microcontroller is meant to be more self-contained and independent, and functions as a tiny, dedicated computer.
he great advantage of microcontrollers, as opposed to using larger microprocessors, is that the parts-count and design costs of the item being controlled can be kept to a minimum.
They are typically designed using CMOS (complementary metal oxide semiconductor) technology, an efficient fabrication technique that uses less power and is more immune to power spikes than other techniques.
Microcontrollers are sometimes called embedded microcontrollers, which just means that they are part of an embedded system that is, one part of a larger device or system
Controller: A device that controls the transfer of data from a computer to a peripheral device and vice versa. For example, disk drives, display screens, keyboards and printers all require controllers. In personal computers, the controllers are often single chips.
When you purchase a computer, it comes with all the necessary controllers for standard components, such as the display screen, keyboard, and disk drives If you attach additional devices, however, you may need to insert new controllers that come on expansion boards.
Controllers must be designed to communicate with the computer’s expansion bus.There are three standard bus architectures for PCs – the AT bus, PCI (Peripheral Component Interconnect ) and SCSI.
When you purchase a controller, therefore, you must ensure that it conforms to the bus architecture that your computer uses.
The following varieties of SCSI are currently implemented:
- SCSI-1: Uses an 8-bit bus, and supports data rates of 4 MBps.
- SCSI-2: Same as SCSI-1, but uses a 50-pin connector instead of a 25-pin connector, and supports multiple devices. This is what most people mean when they refer to plain SCSI.
- Wide SCSI: Uses a wider cable (168 cable lines to 68 pins) to support 16-bit transfers.
- Fast SCSI: Uses an 8-bit bus, but doubles the clock rate to support data rates of 10 MBps.
- Fast Wide SCSI: Uses a 16-bit bus and supports data rates of 20 MBps.
- Ultra SCSI: Uses an 8-bit bus, and supports data rates of 20 MBps.
- Wide Ultra2 SCSI: Uses a 16-bit bus and supports data rates of 80 MBps.
- SCSI-3: Uses a 16-bit bus and supports data rates of 40 MBps. Also called Ultra Wide SCSI.
- Ultra2 SCSI: Uses an 8-bit bus and supports data rates of 40 MBps.
- A specialized computer system that is part of a larger system or machine. Typically, an embedded system is housed on a single microprocessor board with the programs stored in ROM.
- Virtually all appliances that have a digital Interface- watches, microwaves, VCRs, cars -utilize embedded systems.
- Some embedded systems include an operating system, but many are so specialized that the entire logic can be implemented as a single program.