Hardware

Hardware includes devices used to input, process and output data. In this section we take apart a computer to see all the pieces contained in the system unit. The following descriptions are adapted from the website http://www.howstuffworks.com/. This is an excellent website for learning how anything works from cars, trains to computers.

Keyboard
A keyboard is a series of switches connected to a microprocessor that monitors the state of each switch and initiates a specific response to a change in that state.
Mouse
A ball inside the mouse touches the desktop and rolls when the mouse moves. Two rollers inside the mouse touch the ball. One of the rollers is oriented so that it detects motion in the X direction, and the other is oriented 90 degrees to the first roller so it detects motion in the Y direction. When the ball rotates, one or both of these rollers also rotate. The rollers each connect to a shaft, and the shaft spins a disk with holes in it. On either side of the disk there is an infrared LED and an infrared sensor. The holes in the disk break the beam of light coming from the LED so that the infrared sensor sees pulses of light. The rate of the pulsing is directly related to the speed of the mouse and the distance it travels. An on-board processor chip reads the pulses from the infrared sensors and turns them into binary data that the computer can understand. The chip sends the binary data to the computer through the mouse's cord. An optical mouse actually uses a tiny camera to take 1,500 pictures every second. The pictures analyzed many times each second to determines how far the mouse has moved and the coordinates are sent to the computer. The computer moves the cursor on the screen based on the coordinates received from the mouse.
Monitor
Most desktop displays use a cathode ray tube (CRT), while portable computing devices such as laptops incorporate liquid crystal display (LCD), light-emitting diode (LED), gas plasma or other image projection technology. In this section we briefly consider the CRT. In a cathode ray tube, the "cathode" is a heated filament. The "ray" is a stream of electrons that naturally pour off a heated cathode into the vacuum. The stream of electrons is focused by a focusing anode into a tight beam. The high speed beam of electrons flies through the vacuum in the tube and hits the flat screen at the other end of the tube. This screen is coated with phosphor, which glows when struck by the beam. To "paint" the entire screen, electronic circuits inside the monitor use the magnetic coils to move the electron beam in a "raster scan" pattern across and down the screen. The beam paints one line across the screen from left to right. It then quickly flies back to the left side, moves down slightly and paints another horizontal line. When the beam reaches the right side of the bottom line, it moves back to the upper left corner of the screen.
Floppy disk
Similar to a hard disk except it spins much slower and has a much smaller capacity, namely 1.44 MB. The write head puts data on the diskette by magnetizing minute, iron, bar-magnet particles embedded in the diskette surface.
CD
A CD has a single spiral track of data, circling from the inside of the disc to the outside. If this track were straightened and measured, it would be approximately 3.5 miles long. A microscopic pit on this track represents a binary 1 and a smooth area represents a binary 0. A low intensity laser reflects strongly from a smooth area and weakly from a pit. A CD-R drive can be used to write information to a CD once. A CD-RW can be erased and reused. A CD can hold approximately 650 MB of information.
System unit

Motherboard
A motherboard is a multi-layered printed circuit board. Copper circuit paths called traces that resemble a complicated roadmap carry signals and voltages across the motherboard. The motherboard is the main circuit board that all of the other internal components connect to. The CPU and main memory (RAM) are usually on the motherboard along with the graphics card, sound card and modem.
CPU
A microprocessor does three basic things:
Using its ALU (Arithmetic/Logic Unit), a microprocessor can perform mathematical operations like addition, subtraction, multiplication and division. Modern microprocessors contain floating point processors that can perform operations on floating point numbers. A microprocessor can move data from one memory location to another. A microprocessor can make decisions and jump to a new set of instructions based on those decisions.
RAM
RAM is considered "random access" because you can access any memory cell directly. The opposite of RAM is serial access memory (SAM). SAM stores data as a series of memory cells that can only be accessed sequentially. Similar to a microprocessor, a memory chip is an integrated circuit (IC) made of millions of transistors and capacitors. In the most common form of computer memory, dynamic random access memory (DRAM), a transistor and a capacitor are paired to create a memory cell, which represents a single bit of data. The capacitor holds the bit of information -- a 0 or a 1. The transistor acts as a switch that lets the control circuitry on the memory chip read the capacitor or change its state. A capacitor is like a small bucket that is able to store electrons. To store a 1 in the memory cell, the bucket is filled with electrons. To store a 0, it is emptied. The problem with the capacitor's bucket is that it has a leak. In a matter of a few milliseconds a full bucket becomes empty. Therefore, for dynamic memory to work, either the CPU or the memory controller has to come along and recharge all of the capacitors holding a 1 before they discharge. To do this, the memory controller reads the memory and then writes it right back. This refresh operation happens automatically thousands of times per second. The refresh operation is where dynamic RAM gets its name. Dynamic RAM has to be dynamically refreshed all of the time or it forgets what it is holding. The downside of all of this refreshing is that it takes time and slows down the memory. Memory cells are etched onto a silicon wafer in an array of columns (bitlines) and rows (wordlines). The intersection of a bitline and wordline constitutes the address of the memory cell. Static RAM uses a completely different technology. In static RAM, a form of flip-flop holds each bit of memory. A flip-flop for a memory cell takes four or six transistors along with some wiring, but never has to be refreshed. This makes static RAM significantly faster than dynamic RAM. However, because it has more parts, a static memory cell takes a lot more space on a chip than a dynamic memory cell. Therefore you get less memory per chip, and that makes static RAM a lot more expensive. So static RAM is fast and expensive, and dynamic RAM is less expensive and slower. Therefore static RAM is used to create the CPU's speed-sensitive cache, while dynamic RAM forms the larger system RAM space.
Fan
Needed to keep the CPU from overheating.
Ports
All computer operating systems in use today support serial ports, because serial ports have been around for decades. Parallel ports are a more recent invention and are much faster than serial ports. USB ports are only a few years old, and will likely replace both serial and parallel ports completely over the next several years. The name "serial" comes from the fact that a serial port "serializes" data. That is, it takes a byte of data and transmits the 8 bits in the byte one at a time. The advantage is that a serial port needs only one wire to transmit the 8 bits (while a parallel port needs 8). The disadvantage is that it takes 8 times longer to transmit the data than it would if there were 8 wires. Serial ports, also called communication (COM) ports, are bi-directional. Bi-directional communication allows each device to receive data as well as transmit it. If you have a printer connected to your computer, there is a good chance that it uses the parallel port. When a PC sends data to a printer or other device using a parallel port, it sends 8 bits of data (1 byte) at a time. These 8 bits are transmitted parallel to each other, as opposed to the same eight bits being transmitted serially (all in a single row) through a serial port. The standard parallel port is capable of sending 50 to 100 kilobytes of data per second. On to USB (Universal Serial Bus) ports. Anyone who has been around computers for more that two or three years knows the problem that USB is trying to solve -- in the past, connecting devices to computers has been a real headache! Printers connected to parallel printer ports, and most computers only came with one. Things like Zip drives, which need a high-speed connection into the computer, would use the parallel port as well, often with limited success and not much speed. Modems used the serial port, but so did some printers and a variety of odd things like Palm Pilots and digital cameras. Most computers have at most two serial ports, and they are very slow in most cases. Just about every peripheral made now comes in a USB version. A sample list of USB devices that you can buy today includes: Printers - Scanners - Mice - Joysticks - Digital cameras - Webcams - Scientific data acquisition devices - Modems - Speakers - Telephones - Video phones - Storage devices such as Zip drives - Network connections
Sound card
A sound card typically has the following parts. A digital signal processor (DSP) that handles most computations. A digital to analog converter (DAC) for audio leaving the computer. An analog-to-digital converter (ADC) for audio coming into the computer. ROM (read-only memory). Musical instrument digital interface (MIDI) for connecting to external music equipment. Jacks for connecting speakers and microphones, as well as line in and line out. A game port for connecting a joystick or gamepad.
Graphics card
This translates image data from the computer into a format that can be displayed by the monitor. The first thing that a graphics card needs is memory. The memory holds the color of each pixel. The second thing a graphics card needs is a way for the computer to change the graphics card's memory. This is normally done by connecting the graphics card to the card bus on the motherboard. The computer can send signals through the bus to alter the memory. The next thing that the graphics card needs is a way to generate the signals for the monitor. The card must generate color signals that drive the cathode ray tube (CRT) electron beam.
Modem
The word "modem" is a contraction of the words modulator-demodulator. A modem is typically used to send digital data over a phone line. The sending modem modulates the data into a signal that is compatible with the phone line, and the receiving modem demodulates the signal back into digital data. Wireless modems convert digital data into radio signals and back.
Hard drive
Hard disks have a hard platter that holds a magnetic medium. A typical personal computer will have a hard disk with a capacity of between 10 and 40 gigabytes. The interior of a hard disk contains platters made of glass or aluminum that spin at 3600 or 7200 rpm and an arm that holds the read/write heads which are capable of going from the center of the disk to the rim more than 50 times per second. A hard disk stores changing digital information in a relatively permanent form. They give computers the ability to remember things when the power goes out.