The Bit and its offspring...
 Contents Deciphering an Ad Hardware and Software The Bit and its offspring... The CPU Input Devices Output Devices Devices that do Input AND Output Buying a computer Deciphering the ad Laboratory Assignment Summary

### Section: The Bit and its offspring...

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.

## Subsection(s)

• The Bit
• The Byte
• The Kilobyte
• The Megabyte
• The Gigabyte
• ### The Bit

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.

### The Byte

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!)

Q. 1
I recently came across an Internet message which claimed that much of the Internet was a conspiracy by big business. One of the author's more interesting theories was that a certain kind of address information called the ip address was limited to a maximum value of 255 rather than 999 deliberately to reduce the supply of addresses and thus make them more valuable. It is true that these addresses have a maximum value of 255. Can you think of another reason this could be the case?

Q. 2
Many computer monitors are capable of displaying 256 colors at a time. Why this number?

Why isn't it 255?

Q. 3
If you had a document that was 500 bytes long and saved in ASCII format, about how many characters long would the document be?

### The Kilobyte

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.

Q. 4
A later kind of floppy disk was capable of handling 720K. How many bytes is that?

How many bits is it?