# Memory

"Computers only work with binary numbers. A binary number, or bit for short, is the smallest unit of information that is used by a computer and consists of one of two different characters, a 0 or a 1. A 0 would refer to off or false or no, while a 1 would refer to on or true or yes. A simplified example of the use of a bit would be when the computer is booted up, it sends out a signal to the printer connected to the computer to see if it is ready to accept documents. If the printer isn't ready, it would respond by sending back a 0 indicating no, I'm not ready. If the printer is ready, it would respond by sending back a 1 indicating yes, I am ready. When you see the speed rating of a communications device, such as a serial port or a modem, the speed will be listed in bps or bits per second. A modem that has a rating of 56K bps (since K refers to thousand, that is 56,000 bps) would have the capability to sending or receiving 56,000 0s and/or 1s in 1 second.

Since sending out information 1 bit at a time can be rather time consuming for the computer, information is sent as a package of data or instructions called a byte. A byte is made up of 8 bits of information, such as 00000000 or 10101010. Most of a computer's specifications are represented in terms of bytes, such as the computer's memory capacity or the size of a disk drive.

The following table lists the various terms and their associated values:

 Term Symbol Value bit b 0 or 1 byte B 8 bits kilobit Kb 1,024 bits kilobyte KB 1,024 bytes megabit Mb 1,048,576 bits megabyte MB 1,048,576 bytes gigabit Gb 1,073,741,824 bits gigabyte GB 1,073,741,824 bytes terabit Tb 1,099,511,627,776 bits terabyte TB 1,099,511,627,776 bytes

Note in the above table that when referring to computers, the K (thousand) actually refers to 1,024 and not 1,000. Therefore, a document stored on the computer's hard drive that is listed as being 10 KB in size is actually 10,240 bytes (10 times 1,024) and not 10,000 bytes. If a computer contains 32 MB of memory, it actually contains 33,554,432 bytes (32 times 1,048,576) and not 32,000,000.

The speed of a computer depends on the amount of data its processor can manipulate in a given period of time and the processor's clock speed. The amount of data that the processor can handle is called the word size and refers to the number of bits of information that can be processed at a time. An Intel Pentium® processor can handle 64-bit words or 64 bits (0s and 1s) of information at a time. The older 486 computers contained 32-bit processors and could only handle 32 bits of information at a time. Before you jump to conclusions, a 64-bit processor is not necessarily twice as fast as a 32-bit processor. The 64-bit processor may be more than twice as fast in performing some tasks, but less than twice as fast in performing others. Generally speaking though, a 64-bit processor is faster than a 32-bit processor, which is faster than a 16-bit processor.

The clock speed of a processor is measured by the number of electronic pulses it can produce in a second. Clock speed is built into the processor and is measure in megahertz (MHz). Since mega means million and hertz means times (cycles) per second, 200 MHz is 200 million times per second. The electronic pulses affect the speed with which program instructions are executed because instructions are executed at predetermined intervals, which are timed by the electronic pulses. For example, if we had a computer than contained a processor that was running at 200 MHz and it executed an instruction every 100 pulses, it would process 2,000,000 instructions per second (200 million divided by 100). If the computer had a 300 MHz processor and executed an instruction every 100 pulses, it would process 3,000,000 instructions per second." From Dave's Computer Page, Michigan State University.