Computers have a number of measurable properties. They vary greatly in speed, capacity, and power. To discuss these differences, we need some new units of measure.
The basic unit of measure in a computer system is the bit. A bit is one on/off switch. It is the smallest unit in computing, and is the foundation for for everything else. Since bits are binary (remember what that means?) they have widespread implications for how information is stored and measured. The binary numbering system and its related systems (base 8 and 16) are used to measure just about everything in a computer system. This explains why the numbers used to measure computers might seem a little odd to us. We are used to thinking in base 10, but the computer will interpret everything in base 2. A number like 255 is not very pretty in base 10, but in binary notation it is 11111111, which is a clean, lovely number. You will often run across numbers like 8, 16, 32, and 64. These numbers are powers of two, so they are nice and clean in binary notation. Just keep this in mind during our discussions today.
While the bit is undoubtedly important, it can only hold two possible values, 1 and 0. In order to represent anything more complex than the simplest binary values, we have to combine bits. Eight bits are combined into a unit called a byte. Each bit represents one digit of binary notation. If we put eight of these binary digits together we can represent any number from 0 to 255. Zero would be represented by 00000000 in binary, or all eight bits turned off. If all the bits were on, the largest possible value would be 11111111 binary, which translates to 255 decimal. This is a large enough value to be useful. For example, all the values of the ASCII character set can be represented in one byte. (This is not a coincidence!)
Why isn't it 255?
Although bytes are much more useful for keeping track of memory than bits, they are still a little small for measuring larger entities, like disk space, file size, and memory capabilities. Some early floppy disks, for example, could hold 368,640 bytes of information. The numbers were getting too big for humans to handle easily. Computer scientists used kilobytes to measure these larger quantities. No doubt you are familiar with the metric system, and you know that a kilo represents a thousand. E.G. a kilogram = 1000 grams, a kilometer = 1000 meters. In computing, a kilobyte does not mean exactly one thousand. A kilobyte is 1024 bytes.
Why? It all goes back to the binary system. We like the number 1000 because it is easy to work with in base 10. Computers do not naturally work in base 10, but in base 2. 1000 decimal becomes 1111101000 in binary. This is obviously not a convenient number in binary. Fortunately, the binary value 10000000000 is very easy to work with in binary, and it works out to 1024 in decimal. This is close enough to 1000 decimal that we refer to 1024 bytes as a kilobyte. Kilobyte is often abbreviated K. The 368,640 byte disk we referred to before would be called a 360 K disk.
How many bits is it?
The kilobyte is a more convenient unit of measure than the byte, but rapid advances in computing technology made it difficult to work with as well. Computer manufacturers began developing equipment with capacities of many thousands of kilobytes. Once again, computer scientists used a variation of the metric system to save the day. A thousand kilobytes is referred to as a megabyte. Modern floppy drives often have a capacity of roughly 1,440 K. This value is often referred to as 1.44 M. The term Megabyte is often abbreviated Meg, M, or Mb. Disk drives and memory capacity are often measured in megabytes.
Computer technology continues to increase capacity at an amazing rate. There are now disk drives available which are measured in gigabytes. A gigabyte is 1000 megabytes.