A computer is a machine that can represent many, many different types of information. But at their most basic level, these types of information are all represented in terms of one thing. The most fundamental unit of digital information, the bit. A bit is something that can only have one of two states at any one time. One or Zero, On or off, black or white, true, false, yes, no, high-voltage, low-voltage, right, wrong, read, unread, locked, unlocked, win or lose. A bit is very, very simple. But it's also very powerful, because it can represent many things. You might have heard people describe bit as one or zero. But those are only one of the things that a bit can represent. Everything on the list I just described as well as many other things, can be and is represented as a bit on a computer. A bit can be one or zero when it's dealing with numbers, black or white for pictures, or locked or unlocked for security features. Some people might say that a bit is really high or low voltage, because that's how it's represented in physical memory. But the same bit of information might be represented differently when it's copied to a hard disk or DVD or transmitted over optic fibers. A bit is an abstract representation that can represent any duality, any binary distinction between two things. Like anything on a computer, it's this abstraction that gives it its power. It isn't tied to any particular application. It can be used to represent almost anything. But isn't it still a bit too simple. Yes, a bit can represent any two opposites, but there were a lot of things in life that don't just come down to true or false, yes or no. How can bits represent landscape paintings, symphonies, population demographics, and social networks? We can represent many things with bits because we have a lot of them. And I mean a lot. Computer memory is typically measured in gigabytes. A byte is eight bits, and a gigabyte is a billion bytes. So, that's eight followed by nine zeros. Modern hard disks can be measured in terabytes, which would be eight trillion bytes. That's a lot of ones and zeros, or trues and falses. It's combining these bits together that allows us to represent many complex things. A single bit can represent black or white. But by putting together lots of black and white pixels, you can make a picture. As you'll find out in the rest of this topic, by combining a lot of bits together you can make numbers, letters, sounds, pictures, videos, and everything else that you can store on a computer. If you understand how bits work together, then you will have got to grips with a really fundamental part of how computers work.
