How Computers Work. The Boot Process The primary functions of bootstrap are to test the computer hardware .. chartrolywfunccard.tk This book will tell you how they work and no technical much more knowledgeable about how computers work when you are done than when. How a Computer's Long-Term. Process. 2. Memory Works. Chapter 1. Chapter Getting to Know the Hardware. How Disk Drives Save Information.
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The How Computers Work, Interactive Web Version is an enhanced digital copy of Designed for the Web—This new digital edition of How Computers Work is. Los Alamos Science Number 22 How Computers Work. Gerald A. Friedman, Douglas D. Lemon, and Tony T. Warnock an introduction to serial, vector, and. This free book will tell you how computers work, and no technical ; Paperback: pages; eBook HTML, PDF, and Microsoft Word.
Imagine if a computer were a person. Suppose you have a friend who's really good at math. She is so good that everyone she knows posts their math problems to her. Each morning, she goes to her letterbox and finds a pile of new math problems waiting for her attention. She piles them up on her desk until she gets around to looking at them. Each afternoon, she takes a letter off the top of the pile, studies the problem, works out the solution, and scribbles the answer on the back.
She puts this in an envelope addressed to the person who sent her the original problem and sticks it in her out tray, ready to post. Then she moves to the next letter in the pile. You can see that your friend is working just like a computer. Her letterbox is her input; the pile on her desk is her memory; her brain is the processor that works out the solutions to the problems; and the out tray on her desk is her output.
Once you understand that computers are about input, memory, processing, and output, all the junk on your desk makes a lot more sense:. A computer works by combining input, storage, processing, and output. All the main parts of a computer system are involved in one of these four processes. As you can read in our long article on computer history , the first computers were gigantic calculating machines and all they ever really did was "crunch numbers": Today, computers work on a much wider variety of problems—but they are all still, essentially, calculations.
Everything a computer does, from helping you to edit a photograph you've taken with a digital camera to displaying a web page, involves manipulating numbers in one way or another. Calculators and computers are very similar, because both work by processing numbers. However, a calculator simply figures out the results of calculations; and that's all it ever does. A computer stores complex sets of instructions called programs and uses them to do much more interesting things.
Suppose you're looking at a digital photo you just taken in a paint or photo-editing program and you decide you want a mirror image of it in other words, flip it from left to right. You probably know that the photo is made up of millions of individual pixels colored squares arranged in a grid pattern.
The computer stores each pixel as a number, so taking a digital photo is really like an instant, orderly exercise in painting by numbers! To flip a digital photo, the computer simply reverses the sequence of numbers so they run from right to left instead of left to right. Or suppose you want to make the photograph brighter. All you have to do is slide the little "brightness" icon. The computer then works through all the pixels, increasing the brightness value for each one by, say, 10 percent to make the entire image brighter.
So, once again, the problem boils down to numbers and calculations. What makes a computer different from a calculator is that it can work all by itself. You just give it your instructions called a program and off it goes, performing a long and complex series of operations all by itself. Back in the s and s, if you wanted a home computer to do almost anything at all, you had to write your own little program to do it. For example, before you could write a letter on a computer, you had to write a program that would read the letters you typed on the keyboard, store them in the memory, and display them on the screen.
Writing the program usually took more time than doing whatever it was that you had originally wanted to do writing the letter. Pretty soon, people started selling programs like word processors to save you the need to write programs yourself.
Today, most computer users rely on prewritten programs like Microsoft Word and Excel or download apps for their tablets and smartphones without caring much how they got there.
Hardly anyone writes programs any more, which is a shame, because it's great fun and a really useful skill. Most people see their computers as tools that help them do jobs, rather than complex electronic machines they have to pre-program.
Some would say that's just as well, because most of us have better things to do than computer programming. Then again, if we all rely on computer programs and apps, someone has to write them, and those skills need to survive.
Thankfully, there's been a recent resurgence of interest in computer programming. There's a growing hobbyist movement, linked to build-it yourself gadgets like the Raspberry Pi and Arduino. And Code Clubs , where volunteers teach kids programming, are springing up all over the world.
The beauty of a computer is that it can run a word-processing program one minute—and then a photo-editing program five seconds later.
In other words, although we don't really think of it this way, the computer can be reprogrammed as many times as you like. This is why programs are also called software. They're "soft" in the sense that they are not fixed: By contrast, a computer's hardware —the bits and pieces from which it is made and the peripherals , like the mouse and printer, you plug into it —is pretty much fixed when you download it off the shelf.
The hardware is what makes your computer powerful; the ability to run different software is what makes it flexible. That computers can do so many different jobs is what makes them so useful —and that's why millions of us can no longer live without them! Suppose you're back in the late s, before off-the-shelf computer programs have really been invented.
You want to program your computer to work as a word processor so you can bash out your first novel—which is relatively easy but will take you a few days of work.
A few weeks later, you tire of writing things and decide to reprogram your machine so it'll play chess. Later still, you decide to program it to store your photo collection. Every one of these programs does different things, but they also do quite a lot of similar things too.
For example, they all need to be able to read the keys pressed down on the keyboard, store things in memory and retrieve them, and display characters or pictures on the screen. If you were writing lots of different programs, you'd find yourself writing the same bits of programming to do these same basic operations every time.
That's a bit of a programming chore, so why not simply collect together all the bits of program that do these basic functions and reuse them each time? Typical computer architecture: You can think of a computer as a series of layers, with the hardware at the bottom, the BIOS connecting the hardware to the operating system, and the applications you actually use such as word processors, Web browsers, and so on running on top of that.
Each of these layers is relatively independent so, for example, the same Windows operating system might run on laptops running a different BIOS, while a computer running Windows or another operating system can run any number of different applications. That's the basic idea behind an operating system: You can think of an operating system as the "foundations" of the software in a computer that other programs called applications are built on top of.
So a word processor and a chess game are two different applications that both rely on the operating system to carry out their basic input, output, and so on. The operating system relies on an even more fundamental piece of programming called the BIOS Basic Input Output System , which is the link between the operating system software and the hardware.
Unlike the operating system, which is the same from one computer to another, the BIOS does vary from machine to machine according to the precise hardware configuration and is usually written by the hardware manufacturer.
The BIOS is not, strictly speaking, software: Operating systems have another big benefit. Back in the s and early s , virtually all computers were maddeningly different.
They all ran in their own, idiosyncratic ways with fairly unique hardware different processor chips, memory addresses, screen sizes and all the rest. Programs written for one machine such as an Apple usually wouldn't run on any other machine such as an IBM without quite extensive conversion.
That was a big problem for programmers because it meant they had to rewrite all their programs each time they wanted to run them on different machines. How did operating systems help? If you have a standard operating system and you tweak it so it will work on any machine, all you have to do is write applications that work on the operating system.
Then any application will work on any machine. The operating system that definitively made this breakthrough was, of course, Microsoft Windows, spawned by Bill Gates. It's important to note that there were earlier operating systems too. You can read more of that story in our article on the history of computers.
Don't open up your PC unless you really know what you're doing. There are dangerous voltages inside, especially near the power supply unit, and some components can remain live for quite a time after the power has been turned off. Inside the case of a typical PC showing four key areas of components, described below. It all looks pretty scary and confusing inside a typical PC: But work through the components slowly and logically and it all starts to make sense.
Most of what you can see divides into four broad areas, which I've outlined in green, blue, red, and orange on this photo. There's usually a large cooling fan on the outside of the computer case near the power socket or a much smaller fan on a laptop, usually on one side.
The diskettes and CD-ROM disks that you have seen with personal computers are secondary storage devices, as are hard disks. Since the physical attributes of secondary storage devices determine the way data is organized on them, we will discuss secondary storage and data organization together in another part of our on-line readings. Now let us consider the components of the central processing unit.
The Control Unit The control unit of the CPU contains circuitry that uses electrical signals to direct the entire computer system to carry out, or execute, stored program instructions.
Like an orchestra leader, the control unit does not execute program instructions; rather, it directs other parts of the system to do so. A logical operation is usually a comparison. The unit can compare numbers, letters, or special characters. The computer can then take action based on the result of the comparison.
This is a very important capability. It is by comparing that a computer is able to tell, for instance, whether there are unfilled seats on airplanes, whether charge- card customers have exceeded their credit limits, and whether one candidate for Congress has more votes than another.
Logical operations can test for three conditions: Equal-to condition. For example: If the number of tickets sold equals the number of seats in the auditorium, then the concert is declared sold out. Less-than condition. To test for this condition, the computer compares values to determine if one is less than another.
Greater-than condition. In this type of comparison, the computer determines if one value is greater than another. For example: If the hours a person worked this week are greater than 40, then multiply every extra hour by 1.
A computer can simultaneously test for more than one condition. In fact, a logic unit can usually discern six logical relationships: equal to, less than, greater than, less than or equal to, greater than or equal to, and not equal. Registers: Temporary Storage Areas Registers are temporary storage areas for instructions or data. They are not a part of memory; rather they are special additional storage locations that offer the advantage of speed. Registers work under the direction of the control unit to accept, hold, and transfer instructions or data and perform arithmetic or logical comparisons at high speed.
The control unit uses a data storage register the way a store owner uses a cash register-as a temporary, convenient place to store what is used in transactions.
Computers usually assign special roles to certain registers, including these registers: An accumulator, which collects the result of computations.
An address register, which keeps track of where a given instruction or piece of data is stored in memory. Each storage location in memory is identified by an address, just as each house on a street has an address. A storage register, which temporarily holds data taken from or about to be sent to memory.
A general-purpose register, which is used for several functions. Memory and Storage Memory is also known as primary storage, primary memory, main storage, internal storage, main memory, and RAM Random Access Memory ; all these terms are used interchangeably by people in computer circles.
Memory is the part of the computer that holds data and instructions for processing. Although closely associated with the central processing unit, memory is separate from it. Memory stores program instructions or data for only as long as the program they pertain to is in operation.
Keeping these items in memory when the program is not running is not feasible for three reasons: Most types of memory only store items while the computer is turned on; data is destroyed when the machine is turned off. If more than one program is running at once often the case on large computers and sometimes on small computers , a single program can not lay exclusive claim to memory. There may not be room in memory to hold the processed data.