HOW COMPUTERS WORK PDF

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How Computers Work Pdf

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How Computers Use Power. Part 3: How Software. Chapter How Serial Ports Triumph. Works. Chapter Chapter 7. How a Computer Display . 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. HOW COMPUTERS WORK. (The Most Important Discovery by Humans). Steve Krar. A computer, a digital information-processing machine, works by changing.

What is an operating system? 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? Photo: 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: it's the core software in a computer that essentially controls the basic chores of input, output, storage, and processing.

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: it's a program semi-permanently stored into one of the computer's main chips, so it's known as firmware it is usually designed so it can be updated occasionally, however. 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. What's inside your PC? Don't open up your PC unless you really know what you're doing.

How computers work (PDF)

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. Photo: 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: circuit boards like little "cities" with the chips for buildings, rainbow tangles of wires running between them, and goodness knows what else. 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.

In this machine, there are two external fans colored green and blue just to the left, cooling both the power supply and the mainboard.

Mainboard blue As its name suggests, this is the brain of a computer—where the real work gets done. The main processor central processing unit is easy to spot because there's typically a large fan sitting right on top of it to cool it down. In this photo, the processor is directly underneath the black fan with the red central spindle.

Exactly what's on the mainboard varies from machine to machine. Other circuit boards red Although the mainboard can theoretically contain all the chips a computer needs, it's quite common for PCs to have three other separate circuit boards: one to manage networking, one to process graphics, and one to deal with sound.

Some computers have chips that do all their networking on the motherboard.

White Ron. How Computers Work

The graphics card also called the video card or display adapter is the part of a computer that handles everything to do with the display.

Why isn't that done by the central processing unit? In some machines, it can be, but that tends to slows down both the main processing of the machine and the graphics. 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. How do data and instructions get from an input device into memory? The control unit sends them. After being processed, the information is sent to memory, where it is hold until it is ready to he released to an output unit. One thing is certain: the PC will evolve. It will get faster.

It will have more capacity. And it will continue to be an integral part of our lives. Exactly what we represent with which bit isn't important, as long as you understand that 1 is not 0, and 0 is not 1. Where they come from, on the other hand, is from any number of places a computer can interact with. For example, computers run on electricity, so when a computer wants to send information from one place to another it sends these "pulses" of electricity over a wire.

A higher voltage pulse will mean a 1, and a lower voltage pulse will mean a 0. But there are other parts of a computer that still use 0s and 1s that aren't electric, like the hard drive. The hard drive stores 1s and 0s by changing the magnetic poles of small parts of a metal disk. Positive and negative charges would be 1s or 0s. So you can see how these real-life things can be changed to represent bits.

Now you're probably wondering why, and what significance do bits have? How can a 1 or a 0 be turned into important information? However, in summary, we use combinations of bits and say that different combinations have different meanings. So we might say that means the number 2, and means the number 3 which it does, and there is strange math involved that requires re- learning how to count.

From there, as long as everyone agrees that this is the case and these combinations do mean these things, we can start to make bigger groups of these bits that can be interpreted as instructions that can make computers do different things.

Lets dive right into the magical land of data. Whats the symbol for five? Whats the symbol for ten? But wait, isn't that the symbol for one and zero? Right, so in our numbering system, when we get to the number ten, we write the symbol for one and zero.

What is a computer?

There is no symbol for ten, we simply recycle the ones we already have. Because of this, we call our numbering system "base-ten", or "decimal".

What these all are referring to is a different kind of numbering system. For our decimal system, we write a '10' when we get to ten, but for binary, we write a '10' when we get to two.

There is no symbol for two in binary, exactly how there is no symbol for ten in decimal. Cool if not google "binary".

Ok, now for something completely different, but related. Theres something in computer theory called a "logic gate". It's a device. It has two inputs, and one output.

The only input it accepts is "on" or "off", and the output is the same, "on" or "off". You might see the relation to binary. A logic gates output is based on its input.

An example of a logic gate is a "AND" gate. When both of the inputs are on, the output is on. Otherwise, the output is off. You still with me? Don't worry, the cool stuff is coming soon. Another logic gate is the "NOT" gate. The NOT gate has one input.

How Computers Work: The Evolution of Technology, Tenth Edition

If the input is off, the output is on, and vice versa. The output is not the input. Get it?

Creative, I know. We nerds don't get out much. Anyways, try to figure out what the output would be for all the four different possible combinations of the two inputs for the NAND gate.

Now, you have probably heard of computer memory right It's not going to make total sense at first, but that diagram shows a memory-holder- thingamajig. Look at it for a while and try to figure out what it does. Basically it holds a "bit" of memory. You could say that a bit is like one digit of a binary number. You line a bunch of these in a row, and you can start holding numbers. But what do you do with those numbers?

This is where it gets cool. You do math with those numbers. This next device is called an "adder". The gate on top is called an XOR gate, its output is on if only one of its inputs is on. If there both on or off, then the output is off. Now, make it a little more complex and you can add multiple bits at the same time, by linking the last ones "Cout" to the next ones "Cin".

Cool, now we have a basic calculator. How can we turn this up to 11 and make a computer?

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Now, you know what data is, and so code is easy to explain. Its just data. Thats all it is. The reason why its different then other data though, is because the CPU interprets it as instructions. Now, real quick, memory is organized on a computer by something called memory addresses, basically they just allow the CPU to ask for memory at a specific location.

Generally speaking the addresses are sized by "bytes" which is just another word for "eight bits". So if we wanted to access memory location five or whatever we could store that as ''. But hold on, how does the CPU know where to get its instructions?

On the cpu, Theres a tiny amount of memory, it does various things, such as hold something called the "instruction pointer".

The instruction pointer holds the address of the next instruction, and increments itself after every instruction.All the main parts of a computer system are involved in one of these four processes. The boot loader is a small program designed to find and launch the PC's operating system.

Network interfaces, including managing your Internet connection, also fall into the device management bucket. This is why programs are also called software. Inside the case of a typical PC showing four key areas of components, described below. Mobile Computing. The boot disk is typically the same hard disk or solid-state drive that contains your operating system.

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