The five classic components of a computer are input, output, memory, datapath, and control. Datapath and control are combined and called as the processor.
COMPONENTS OF A COMPUTER SYSTEM The five classic components of acomputer are input, output, memory, datapath, and control. Datapath and controlare combined and called as the processor. The figure 1.1 shows the standardorganization of a computer. This organization is independent of hardwaretechnology. Theorganization of a computer, showing the five classic components. 1. Inputwrites data to memory 2. Outputreads data from memory 3. Memorystores data and programs 4. Controlsends the signals that determine the operations of the datapath, memory, input,and output. 5. Datapathperforms arithmetic and logic operations Fig.1.1The organization of a computer
Two key components of computers:
1. Inputdevices, such as the keyboard and mouse,
2. Outputdevices, such as the screen.
·Input device - A mechanism through which thecomputer is fed information, such as the keyboard or mouse.
·Output device - A mechanism that conveys theresult of a computation to a user or another computer.
As the names suggest, input feedsthe computer, and output is the result of computation sent to the user. Somedevices, such as networks and disks, provide both input and output to thecomputer.
Input Device
The most commonly used inputdevice is a keyboard. Whenever the user presses a key the control signal besent to the processor. The processor respond for that by displaying thecorresponding character on the display.
The next commonly used inputdevice is a mouse.The original mouse was electromechanical and used a largeball. When it is rolled across a surface, it would cause an x and y counter tobe incremented. The amount of increase in each counter told how far the mousehad been moved.
The electromechanical mouse hasbeen replaced by the optical mouse. The optical mouse is actually a miniatureoptical processor including an LED to provide lighting, a tiny black-and-whitecamera, and a simple optical processor. The LED illuminates the surfaceunderneath the mouse; the camera takes 1500 sample pictures a second under theillumination. Successive pictures are sent to a simple optical processor thatcompares the images and determines whether the mouse has moved and how far.
Output Device
The most fascinating I/O deviceis probably the graphics display. Most personal mobile devices use liquidcrystal displays (LCDs) to get a thin, low-power display. The LCD is not thesource of light; instead, it controls the transmission of light. A typical LCDincludes rod-shaped molecules in a liquid that form a twisting helix that bendslight entering the display, from either a light source behind the display orless often from reflected light.
Today, most LCD displays use anactive matrix that has a tiny transistor switch at each pixel to preciselycontrol current and make sharper images. As in a CRT, a red-green-blue maskassociated with each pixel determines the intensity of the three colorcomponents in the final image; in a color active matrixLCD, there are three transistor switches at each pixel.
The computer hardware supports arefresh buffer, or frame buffer, to store the bit map. The image to berepresented on-screen is stored in the frame buffer, and the bit pattern perpixel is read out to the graphics display at the refresh rate.
Pixel - The smallest individualpicture element. Screen are composed of hundreds of thousands to millions ofpixels, organized in a matrix.
Fig.1.2Frame Buffer
Each coordinate in the framebuffer on the left determines the shade of the corresponding coordinate for theraster scan CRT display on the right. Pixel (X0, Y0) contains the bit pattern0011, which is a lighter shade of gray on the screen than the bit pattern 1101in pixel (X1, Y1).
Processor
Central processor unit (CPU) -Also called processor. The active part of the computer, which contains thedatapath and control and which adds numbers, tests numbers, signals I/O devicesto activate, and so on. The processor gets instructions and data from memory.
·Datapath - The component of the processor thatperforms arithmetic operations.
·Control - The component of the processor thatcommands the datapath, memory, and I/O devices according to the instructions ofthe program.
Memory
·Memory The storage area in which programs are keptwhen they are running and that contains the data needed by the runningprograms.
·Primary memory - Also called main memory. It is aVolatile memory used to hold programs while they are running;typically consists of DRAM in today’s computers.
·Dynamic random access memory (DRAM) Memory builtas an integrated circuit, it provides random access to any locationSecondarymemory Non- volatile memory used to store programs and data between runs; typicallyconsists of magnetic disks in today’s computers.
·Magnetic disk (also called hard disk) A form ofnonvolatile secondary memory composed of rotating platters coated with amagnetic recording material.
·Cache memory A small, fast memory that acts as abuffer for a slower, larger memory. Cache is built using a different memorytechnology, static random access memory (SRAM). SRAM is faster but less dense,and hence more expensive, than DRAM.
·Volatile memory Storage, such as DRAM, that onlyretains data only if it is receiving power.
·Nonvolatile memory A form of memory that retainsdata even in the absence of a power source and that is used to store programsbetween runs. Magnetic disk is nonvolatile and DRAM is not.
Removable storage technologies:
·Optical disks, including both compact disks (CDs)and digital video disks (DVDs), constitute the most common form of removablestorage.
·Magnetic tape provides only slow serial access andhas been used to back up disks, in a role now often replaced by duplicate harddrives.
·FLASH-based removable memory cards typicallyattach by a USB (Universal Serial Bus) connection and are often used totransfer files.
·Floppy drives and Zip drives are a version ofmagnetic disk technology with removable flexibledisks. Floppy disks were the original primary storage for personal computers,buthavenow largely vanished.
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