Byte Prefixes and Binary Math
When you start talking about lots of bytes, you get into prefixes like kilo, mega and giga, as in kilobyte, megabyte and gigabyte (also shortened to K, M and G, as in Kbytes, Mbytes and Gbytes or KB, MB and GB). The following table shows the binary multipliers:
2^10 = 1,024
2^20 = 1,048,576
2^30 = 1,073,741,824
2^40 = 1,099,511,627,776
2^50 = 1,125,899,906,842,624
2^60 = 1,152,921,504,606,846,976
2^70 = 1,180,591,620,717,411,303,424
2^80 = 1,208,925,819,614,629,174,706,176
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 2 gig hard drive," what he or she means is that the hard drive stores 2 gigabytes, or approximately 2 billion bytes, or exactly 2,147,483,648 bytes. How could you possibly need 2 gigabytes of space? When you consider that one CD holds 650 megabytes, you can see that just three CDs worth of data will fill the whole thing! Terabyte databases are fairly common these days, and there are probably a few petabyte databases floating around the Pentagon by now.
Binary math works just like decimal math, except that the value of each bit can be only 0 or 1. To get a feel for binary math, let's start with decimal addition and see how it works. Assume that we want to add 452 and 751:
452 + 751 --- 1203
To add these two numbers together, you start at the right: 2 + 1 = 3. No problem. Next, 5 + 5 = 10, so you save the zero and carry the 1 over to the next place. Next, 4 + 7 + 1 (because of the carry) = 12, so you save the 2 and carry the 1. Finally, 0 + 0 + 1 = 1. So the answer is 1203.
Binary addition works exactly the same way:
010 + 111 --- 1001
Starting at the right, 0 + 1 = 1 for the first digit. No carrying there. You've got 1 + 1 = 10 for the second digit, so save the 0 and carry the 1. For the third digit, 0 + 1 + 1 = 10, so save the zero and carry the 1. For the last digit, 0 + 0 + 1 = 1. So the answer is 1001. If you translate everything over to decimal you can see it is correct: 2 + 7 = 9.
To see how boolean addition is implemented using gates, see How Boolean Logic Works.
To sum up, here's what we've learned about bits and bytes:
- Bits are binary digits. A bit can hold the value 0 or 1.
- Bytes are made up of 8 bits each.
- Binary math works just like decimal math, but each bit can have a value of only 0 or 1.
There really is nothing more to it -- bits and bytes are that simple.
For more information on bits, bytes and related topics, check out the links below.