2.2: Digital information- Megabytes, gigabytes and terabytes

In the ensuing chapters, you will learn to create several types of digital files: Audio files, photograph files and video files. It is important that you understand how to “weigh” these files since, as we will soon discuss, the larger the file size, the longer it takes to download over the Internet.

When it comes right down to it, this whole digital evolution can be explained in bits and bytes. A byte is a unit of measure for digital information. A single byte contains eight consecutive bits and is capable of storing a single ASCII (pronounced as-kee) character.

The American Standard Code for Information Interchange (ASCII) first published a standard in 1967. It defines the 95 printable characters that are the text in computers and communications devices. Essentially, it’s everything on your keyboard: letters, numbers and basic symbols like % and &.

To make it easier to talk about a lot of bytes, we use prefixes like kilo, mega and giga, as in kilobyte, megabyte and gigabyte (also shortened to K, M and G, as in KB, MB and GB). The table on the next page shows the number of bytes contained in each.

You can see in this chart that kilo is about a thousand, mega is about a million, giga is about a billion, and so on. So when someone says, “This computer has a 40 gig hard drive,” that means the hard drive stores 40 gigabytes, or approximately 40 billion bytes. How could you possibly need 40 gigabytes of space? Well, one CD holds 650 megabytes, so it won’t take long to fill the whole thing, especially if you have a lot of music and digital photographs. Petabyte databases are actually common these days, from the Pentagon to such major retailers as Sears, who use them to store customer data.

Source: Marshall Brain, “How Bits and Bytes Work,” April 1, 2000. http://computer.howstuffworks.com/bytes3.htm (January 27, 2007).

Think of it this way: A petabyte is the equivalent of 250 billion pages of text, enough to fill 20 million four-drawer filing cabinets. Or imagine a 2,000-mile-high tower of 1 billion diskettes.

So what does it mean? For starters, you should never send an e-mail with an attachment larger than 1MB or you will clog your server and the server of the person you’re sending it to. And you should especially never send an e-mail with a large attachment such as a photo to a group list. The server will have to make copies of your large file for everyone on the distribution list. (Instead, copy it to a USB drive, burn it to a disk or upload it to an FTP server. More on this later.)

You should also begin to recognize how large the files (PDFs or video clips) are that you download from the Web. Note how long it takes to download a file that is 500KB versus one that is 5MB. It’s part of the digital literacy lesson you’ve begun to learn.

This is important for online publishing because the speed of an Internet connection plus the size of the file to be downloaded determines how fast someone can download your content. If it’s just text, like a news story, it’s probably only a few KB and will download quickly, even over an old 56K dial-up modem.

Note

The “56K” refers to the transfer rate per second of digital information. So dial-up users with 56K modems can’t expect to download information over the Internet faster than 56KB per second.