If you've ever found out that an email wouldn't go through because the attachment was "too big", or if your iPod ever got full, or the memory card on your digital camera was used up, you know that digital information has a physical size. But without a reference point, what is "too big" or "too much?"
Let's ignore "memory" or "bandwidth" or other such concepts for now and focus on digital storage. The smallest unit of measurement, for practical purposes, in a digital file is called a "byte". And even that is really too small to use.
A kilobyte is 1,000 bytes. Most files can be measured as in kilobytes. For example, the Word document that you just wrote is probably about 200 kilobytes. A kilobyte is usually just called a "K".
A megabyte is 1,000 times more than a "K". You see it abbreviated as "MB". Audio and video files are much bigger than text files so they are measured in Megabytes
A gigabyte is 1,000 time more than a "MB". This is used to measure storage and large video files. It's usually just called a "Gig", or "G".
I won't go on and on with various trivia and other file sizes. That's what makes this all so confusing. As of this writing, in 2010, Kilobyte, Megabyte and Gigabyte is all you have to know.