In my previous article I outlined the history of computers and explained their development into what we recognise today. I described that computers are, in one way or another, simply calculating devices based on numbers. But how do they actually work?
Note for Computer Experts! The description that follows is a very simplified explanation of the workings of a computer. It is not intended to be a definitive or exhaustive account, is not meant as a textbook and probably has more holes than a block of Gruyere cheese. E&OE (Errors and omissions Excepted) as they say in legal contracts.
This post seeks to explain the basics of computer workings and how they rely upon a set of instructions (a programme) to carry out a particular task or tasks. Remember the earlier description of the Jacquard Loom and how different cloth patterns could be produced using a different punched card for each pattern? In this instance, the operation of the loom was mechanical - a hole in the punched card corresponding to a lever which was activated as the card passed through the loom. The card's passage through the loom was controlled by turning a wheel using a handle or foot pedal. Later models provided power by an engine which worked either by fuel or electricity. Essentially however, the machines were still analogue whereby a physical action created a machine response.
As we progressed into the 20th century we saw the introduction of electrical impulses to trigger certain actions in a computer. Unlike the earlier mechanical calculators (controlled by hand, foot or even electricity turning cogs or levers), an electronic computer works in a fundamentally different way. Here, a power source in the form of a spark of electricity creates a direct response from a component in the computer. To understand the principle think of a light switch which, when pressed, lets electricity flow that then causes the light bulb to light up. The light is said to be ON. Switch again and the light goes out and is said to be OFF.
Now imagine the computer is a box full of light bulbs each controlled by a switch. By depressing the switches you can light up the bulbs in any order you wish. The earliest electronic computers were essentially just this except that instead of light bulbs the computer held valves that lit up. In my earlier history I spoke of the first large computer called Colossus. Here is a picture of it showing the valves (photo by courtesy of the Crypto Museum).
Note for Computer Experts! The description that follows is a very simplified explanation of the workings of a computer. It is not intended to be a definitive or exhaustive account, is not meant as a textbook and probably has more holes than a block of Gruyere cheese. E&OE (Errors and omissions Excepted) as they say in legal contracts.
This post seeks to explain the basics of computer workings and how they rely upon a set of instructions (a programme) to carry out a particular task or tasks. Remember the earlier description of the Jacquard Loom and how different cloth patterns could be produced using a different punched card for each pattern? In this instance, the operation of the loom was mechanical - a hole in the punched card corresponding to a lever which was activated as the card passed through the loom. The card's passage through the loom was controlled by turning a wheel using a handle or foot pedal. Later models provided power by an engine which worked either by fuel or electricity. Essentially however, the machines were still analogue whereby a physical action created a machine response.
As we progressed into the 20th century we saw the introduction of electrical impulses to trigger certain actions in a computer. Unlike the earlier mechanical calculators (controlled by hand, foot or even electricity turning cogs or levers), an electronic computer works in a fundamentally different way. Here, a power source in the form of a spark of electricity creates a direct response from a component in the computer. To understand the principle think of a light switch which, when pressed, lets electricity flow that then causes the light bulb to light up. The light is said to be ON. Switch again and the light goes out and is said to be OFF.
Now imagine the computer is a box full of light bulbs each controlled by a switch. By depressing the switches you can light up the bulbs in any order you wish. The earliest electronic computers were essentially just this except that instead of light bulbs the computer held valves that lit up. In my earlier history I spoke of the first large computer called Colossus. Here is a picture of it showing the valves (photo by courtesy of the Crypto Museum).
Now, let's imagine a simple computer with FOUR light bulbs/valves. If all these bulbs could be ON or OFF, computer designers realised that you could use the particular pattern of ONs and OFFs to represent a sequence of numbers. In fact, with just four bulbs you can represent the numbers 0 up to 15 - a total of 16 numbers (0 counting as a number of course). Here is a picture of what that sequence would look like (naturally the yellow represents a lit light).
On the left are the numbers 0 - 15 in our normal DECIMAL form. On the right is each corresponding light pattern in what is called BINARY form. Binary (meaning two) because there are only two ways a light can exist - either ON or OFF. All modern computers work in binary arithmetic. Because the binary system uses the two digits 0 & 1 it is said to be Digital. In the picture above, each of the lights is called a BIT and a group of them together is called a BYTE. Although I haven't shown the full sequence, computers work in groups of eight bits and thus the standard computer unit is a byte of eight bits (in the jargon an eight bit byte).
There now follows a light bulb moment.
There now follows a light bulb moment.
Now you can begin to see where the term Megabyte - MB - comes from (Mega is the term for one million). Note, however, that Mb (lower case letter b) means Megabits. Why is this important? Well computers represent their symbols in BYTES but when we talk about communication speeds we always use BITS. Therefore, since a BIT is an eighth of a BYTE, a broadband speed of 2Mb is actually only 250,000 BITS not 2 million - quite a difference. If you wish to download a file that says it is 100MB in size and you have a download speed of 100Mbps (Megabits per second) it will not take you 1 second to download but 8 seconds. Remember this when you next look at adverts for broadband speeds and note that they say "Mbps".
Have I now got you really confused? Didn't I say I would use simple language? Don't worry; take it slowly and read the last bit again. If it still doesn't make sense, don't panic because you don't need to know it to use a computer.
Storing Letters
Okay, so that's alright for numbers but how does a computer store letters (A, B, C....)? This is made possible because we can use a separate code where certain binary numbers can also represent alphabetic letters. This code is called ASCII code which stands for American Standard Code for Information Interchange (ASCII) and it has been around since 1963. Thus the binary number 01000001 (which is 65) can also be read by a computer as the upper case letter A. Hopefully you can see that to create a string of letters the computer actually stores a series of numbers representing those letters. Lesson Over! If you wish to know more about the ASCII code you can go to this Wikipedia article.
Programming
The next stage in telling you how computers work is to look at the role of programming. However, we'll leave that for the next article.
Okay, so that's alright for numbers but how does a computer store letters (A, B, C....)? This is made possible because we can use a separate code where certain binary numbers can also represent alphabetic letters. This code is called ASCII code which stands for American Standard Code for Information Interchange (ASCII) and it has been around since 1963. Thus the binary number 01000001 (which is 65) can also be read by a computer as the upper case letter A. Hopefully you can see that to create a string of letters the computer actually stores a series of numbers representing those letters. Lesson Over! If you wish to know more about the ASCII code you can go to this Wikipedia article.
Programming
The next stage in telling you how computers work is to look at the role of programming. However, we'll leave that for the next article.
