Wednesday, August 10, 2011

Filesize: in physical terms

Kilobyte. Megabyte. Gigabyte. And now Terabyte. We here these terms very frequently when talking about storage space and file sizes- but what do they mean? How do they translate to items we're familiar with?

A bit is a 0 or 1. A byte - a unit capable of handling one letter, or one basic color - is equal to 8 bytes. Everything is expressed in terms of bytes.

A kilobyte is 1 000 bytes.
A megabyte is 1 000 000 bytes.
A gigabyte is 1 000 000 000 bytes.
A terabyte is 1 000 000 000 000 bytes.

(There are also binary versions, using 1024, 1048576, etc bytes, but they don't differ by more than a few percent.)

The smallest .txt files are about 4 kilobytes. A Word document starts at 12 kilobytes and a three-page essay is about 25kb. An image from a digital camera is between one and 6 megabytes. A four-minute mp3 song is about 10Mb. Photoshop CS5 - one of the largest programs in existence - requires up to 1GB of space to install.

Now, consider a piece of ordinary 8.5 x 11 (A4) paper. At 80 zeroes and ones (10 bytes) per line, 25 lines per side, 2 sides per page, a single sheet of paper works out to 500 bytes, or half a kilobyte.

Two sheets of paper, then, are equal to one kilobyte. One megabyte (2000 sheets) will stack about 6 inches high. One gigabyte (2 million sheets) of paper will fill a 5-foot cube, or one minivan - and weight 6 tons. One terabyte of data stored in this manner would require 33 C-5 Galaxy heavy lift cargo planes to carry.

But that's a wholly inefficient method of storage - we have more characters than just 0s and 1s to write. What about writing?

An average book is six by eight by one inch, 400 pages long, and has 200,000 words averaging five letters long. That works out to one million characters (plus 200,000 for the spaces), or about 1.2 megabytes. (The bible is about 4MB and was formerly a standard unit of storage capacity.

One gigabyte would then be 800 books, or several bookcases, or a 34-inch cube, weighing 1400 pounds. One terabyte would be 800,000 books, or 20 mid-sized libraries, and would require just 4 jets to carry.

Okay, then, we're gonna use electronic media. What about the good old floppy disk? It's nothing great, but at 1.44Mb in a small package (3.5" by 3.5" by 0.1") it's still superior to written storage.

One gigabyte of disks (700 disks) would stack to 7 inches square and 2 feet high. Weighing 'just' 31 pounds. You could carry a gigabyte of floppies in a milk crate. Even a terabyte of floppies could be delivered in a single 18-wheeler.

CDs, at 700 megabytes each, are even more efficient. One gig fits on a pair of CDs with room to spare. You could fit a terabyte's worth in the trunk of a small car and still have room for a cooler.

Modern memory, though, is even better. A 32 gigabyte flash drive can be held in the palm of your hand. My new laptop (more on that later) has a 500 GB hard disk...and that's the standard model. For less than 100 dollars, you can now buy a one-terabyte external hard drive that weighs just a few pounds and is smaller than a hardcover book.

The winner, though, is still the human brain. One thousand terabytes (one petabyte) of storage in just three pounds. But, for the first time in history, one dedicated person could probably acquire enough storage to match that.

1 comment:

DTH Rocket said...

Someone once told me (or maybe I read it somewhere) that if you compare the number of synapses in the human brain to computer memory, it was only like 100 MB, but I thought that was a little off... ;)