Chapter 16-Inside the Computer Transistors and Integrated Circuits

NMOS transistor

is negatively doped, so that the switch is open when there is no current, but closes when there is current.

PMOS Transistor

is positively doped, so that the switch is closed when there is no current on the control wire, but opens when current is applied.

AND gate

produces voltage on its output wire if both input wires carry voltage -AND GATE input1 input2 AND output 0 0 0 0 1 0 1 0 0 1 1 1

OR gate

produces voltage on its output wire if either input wire carries voltage -AND, OR, and NOT gates can be combined to construct all the circuitry required to store and manipulate information within a computer

Components of a computer

require electrical power to carry out their assigned task. -electricity generates the light that shines through a computer screen, illuminating the individual pixels that make up images and letters. -electricity runs the motor that spins the harddrive disk, allowing information to be accessed -main memory and cpu employ elcetrical signals to store and manipulate data -bit patterns are represented by the presence or absence of electrical current along a wire.

NOT gate

the flow of electricity is manipulated so that the output signal is always opposite of the input signal. -0 represents no current; 1 represents current note:NOT gates invert voltages in the same way that the JavaScript NOT operator (!) inverts Boolean values 0 corresponds to false; 1 corresponds to true

Definition of Gate

the term gate suggest a simple circuit that controls the flow of electricity

Gates to circuits

transistors are connected to form basic logic gates, which are then combined to build more advanced circuitry -we can represent a 4-bit binary number using 4 wires -current on a wire signifies a 1 bit for that place; no current signifies 0

Gates

transistors can be combined to form a circuit, which controls the flow of electricity in order to produce a particular behavior.

Transistors

-A transistor is a solid piece of metal attached to a wire that serves as a switch by alternatively conducting or resisting electricity. -Transistors allow the development of smaller, faster machines at a lower cost. -through a process known as doping, impurities are added to a slab of silicon, causing the metal to act as an electrical switch.

Electricity Basics

-electricity is a flow of electrons, the negative charged particles in atoms, through a medium. good conductors of electricity allow for the flow of electrons with little resistance (e.g., copper, silver, gold) other elements, especially nonmetals, are poor conductors (e.g., carbon, oxygen) -electricity can be quantified in amperes or voltage. amperes gauge electron flow: 1 amp is equal to 6.24 quintillion electrons flowing past a given point each second voltage measures the physical force produced by the flow of electrons: standard household in United States has 110 to 120 volt outlets

Example of how Gates work

-if no current (0 volts) is applied to the input wire, the PMOS transistor will close to allow current to travel on the output wire, and the NMOS transistor will open to disconnect the ground -if current (5 volts) is applied to the input wire, the PMOS transistor will open to disconnect the output wire, and the NMOS transistor will close to ground the input -the end result is that the output is the opposite of the input -this circuit known as a NOT gate

Switch

-the most basic tool for controlling the flow of electricity is a switch. A switch can be flipped to connect or disconnect two wires, thus regulating the flow of electricity between them.

Modern Computers

are powered by electricity, using electrical signals to store and manipulate information.