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HARDWARE: CENTRAL PROCESSOR UNIT (CPU): Heart of the PC - it contains the microprocessor. The CPU is a set of miniaturized circuits that does all the "thinking". It controls the interpretation (arithmetic-logic unit) and execution (control unit) of instructions. It is this CPU in conjunction with RAM that comprise the computer's "brain". The CPU does the "thinking/calculating" while RAM contains the instructions or "memories". It is the CPU that largely determines the operating speed of the computer. BIT: Smallest unit of information recognized by the computer. BIT is short for Binary Digit. A Binary Digit can be either a 0 or a 1. Several bits make up a byte. BYTE: A group of 8 BITS. This grouping of adjacent binary digits (bits) is operated on by the computer as a unit. Computers use 1 BYTE to represent 1 character such as a letter of the alphabet, a number, a punctuation mark, a space, etc. A BYTE is also a unit of measure since it represents 1 character. For example, when the letter "A" is pressed, the keyboard actually sends the following to RAM: 10000001 - a set of 8 bits. See RAM, FLOPPY DISK. RANDOM ACCESS MEMORY (RAM): A set of miniaturized circuits which represents the working memory of the computer. This is where application programs (software) can be loaded from the outside and then executed. The larger the RAM the better. A typical single-user computer system may contain approximately 640,000 bytes of RAM. (This is often abbreviated as 640k RAM: 1 k bytes is actually = 1024 bytes) The RAM is emptied when the computer is turned off - thus it is often called "volatile" memory. WHAT YOU SEE ON YOUR COMPUTER MONITOR IS ACTUALLY IN RAM ONLY - a temporary storage location. To make it permanent we "save" it, or "write" it to a floppy disk or hard drive. These devices are not volatile storage - they do not require electricity. READ ONLY MEMORY (ROM): This is a special section of memory that contains instructions which are activated each time the computer is turned on. These instructions are set at the factory and cannot be changed - thus, they can only be "read" not written to. ROM instructions perform equipment checks and initialization of the computer prior to each use. DISK DRIVE: The port in which a floppy disk is inserted. Device that "reads" data from a magnetic disk and copies it into the computer's memory (RAM) so it can be used by the computer, and that "writes" data from the computer's memory onto a disk so it can be stored for later use. Each Disk Drive is labeled A,B,C,etc because we often must tell the computer which drive has the disk with the information or where to send the information. A Disk Drive reads and writes on a 5.25 inch or 3.5 inch floppy disk. FLOPPY DISKS: The most commonly used mass storage device. Allows entering programs to RAM and saving data from RAM. Will hold data even after the computer is turned off. Data on these disks is stored in concentric rings called tracks. The Disk surface is a thin piece of mylar and is coated with a magnetized material similar to audio or video tape. The read/write heads can magnetize and demagnetize the coated surface repeatedly. Therefore, the Disk can be used, erased, and reused indefinitely. An IBM PC disk holds approximately 360k worth of information (250 double-spaced pages of text). This is called a Double-sided, Double-density Diskette. Newer, smaller 3.5 inch disk exist which hold at least twice as much - 720k. FIXED DISK DRIVE: Usually named disk drive C. It is essentially a very large floppy disk. This Fixed Disk (commonly called a Hard Drive) is secured within the machine and cannot be seen or transported. The storage capacity is so large it is measured in megabytes (1M = 1K squared = 1,048,576 bytes). Fixed Disks are available from 5M on up. The advantage is that it is enough space to meet most users' total storage needs, operates much faster than a floppy (5-10x faster), and is less likely to fail since it lives within the protected computer. KEYBOARD: Input device that lets you enter data into the computer. The layout is similar to the standard QWERTY typewriter keyboard, however there are many extra special keys that are defined by the software you are running. MONITOR: A television-like device that the computer uses to communicate with you. Typically the monitor displays 80 columns (characters) by 25 rows (lines) of information. PRINTER: Most users get at least one Printer for their computer. It produces a "Hard-Copy" output of your data rather than just being able to view it on the monitor. Dot- Matrix printers are inexpensive and fast and can draw graphics. Letter-Quality printers are more expensive and slower but create pages better than typewritten (even pressure on each keystroke). MODEM: Short for Modulator/Demodulator. A device to send and receive computer output over telephone lines. ???????????? ????????? ?KEYBOARD ? ??????? ?MONITOR? ?Mouse ????? INPUT ????>? CPU ?????? OUTPUT ??>?Printer? ?Light Pen ? ? RAM ? ?Plotter? ?Microphone? ??????? ?Speaker? ?Joystick ? ? INPUT ????????? ???????????? ? and/or ? OUTPUT ????????????????????????????????????????????????????????? ? DISK STORAGE, Tape Storage, Modem, Fixed Disk Storage ? ?????????????????????????????????????????????????????????