Technology in Focus Switches A computer system can be viewed as an enormous collection of on off switches System unit is the box that contains the central electronic components of the computer Electrical switches Computers work exclusively with numbers not words Everything a computer does such a processing data or printing a report is broken down into series of 0s and 1s o Binary language Electrical switches are inside the computer and can be flipped between these two states 1 and 0 On off button on DVD o On is pushed in o Off is popped out Vacuum Tubes Earliest generation of electronic computers used devices called vacuum tubes Act as computer switches by blocking the flow of electrical current Takes up a lot of space First high speed digital computer o ENIAC Produce a lot of heat and burn out frequently Two major revolutions for smaller and faster computers were o Invention of transistor o Fabrication of integrated circuits Transistors insulator Are electrical switches built out of semiconductor either by conducting electricity or act as an o Silicon is the semiconductor material used to make transistors o Need specific chemicals to turn on and if not then it turns off acting like a switch Early transistors were separate units of metal rods o Smaller produce little heat quick switching and less expensive Integrated Circuits Are tiny regions of semiconductor material such as silicon Most integrated circuits are no more than a quarter inch in size Integrated circuits have enabled microprocessors which are chips that contain a CPU o Marked the beginning of the true miniaturization of computers More than 2300 transistors The Binary Number System A number system is an organized plan for representing a number Base 10 number system also known as decimal notation uses 10 digits 0 9 6954 6 1000 9 100 5 10 4 1 6 103 9 102 5 101 4 100 o Final number 1 is represented as 100 The binary number system is also referred to as the base 2 number system o Can still represent all the values that a base 10 number system can The binary number system describes a number as the sum of powers of 2 o Codes for numbers letters and instructions Representing Integers In the base 10 number system a whole number is represented as the sum powers of 10 Binary system works by describing a value as the sum of groups of 1s 2s 4s 8s etc o Powers of 2 1 2 4 8 etc Number 67 o Base 10 6 101 7 100 o Binary base 2 26 64 you have 3 left over so 32 16 8 and 4 will be 0s because they cannot contribute You can have 1 group of 2 and 1 group of one 1000011 Doing this on Windows calculator from the programmer selection is much easier because it converts it from decimal to binary automatically Hexadecimal notation is used to make expression of long numbers easier o Base 16 number system 0 9 plus letters A 10 B 11 etc Representing characters ASCII This converts letters and other symbols that we understand to a binary state that the computer can understand Older mainframes used EBCDIC while today s personal computers use ASCII o ASCII represents each letter or character as an 8 bit binary code Remember that a binary digit is a bit and 8 bits is a byte o Each single alphabetical or special character is 1 byte 8bits Total of 8 0s and 1s Upper and lowercase letters have different codes Representing characters Unicode ASCII code can only assign 256 28 different codes ASCII codes cannot represent all languages and symbols because some languages requires more than 256 characters and letters o Unicode was created to solve this Uses 16 bits and can code 1 115 000 different codes Anticipated to replace ASCII First 128 are identical to ASCII Representing decimal numbers Institute of electrical and electronics engineering IEE established a standard called the floating point standard that describes how numbers with fractional parts should be represented o 32 bit system 0 75 Next bit is for magnitude of number hundreds tens etc Last 23 bits are to store the number value First tells you neg or positive Interpretation Unicode or ASCII pattern as a character The CPU machine cycle Decimal numbers are stored by IEEE standards while alphabet and symbols are stored by Certain instructions tell the CPU to expect a negative number next or to interpret the following bit o CPU ALWALYS knows which interpretation to use for a series of bits Also called processing cycle from RAM into CPU language the actual work o Fetch o Decode o Execute o Store The system clock in one of the registers built in CPU It is the internal clock that is a special crystal that acts like a metronome to keep the steady beat o Steady beat or ticks are called clock cycle which set the pace The pace known as clock speed is measured in GHz Control unit Manages the switches of CPU Designed to remember the sequence of processing stages and how each switch should be positioned with each beat of the system clock Stage 1 The fetch stage Cache memory RAM is direct and fast way to access instructions and program information Faster than RAM Avoids the CPU from needing to fetch instructions from RAM every time Before going to RAM the CPU will look in o Level 1 cache memory Block of memory that is built onto the CPU chip to store data and commands that have just been used o Level 2 cache memory Farther from CPU than level 1 Has more storage o Level 3 cache memory Can hold an entire program Can t upgrade cache More cache the better performance speed of your computer Stage 2 The decode stage Collection of commands a specific CPU can execute is called instruction set o Each CPU has its own unique instruction set Because humans are the ones who write the initial instructions it is written in an easier language called assembly language o ADD for addition DIV for divide etc o Translated into long strings of binary code called machine language Control unit uses this to set up the hardware in the CPU for the rest of the Stage 3 The execute stage operations Arithmetic logic unit ALU does CPU mathematical operations and logical operations such as AND OR and NOT Fed data from the CPU s registers The number of bits a computer can work with at a time is referred to as word size o 64 bit vs 32 bit Stage 4 The store stage Making CPUs even faster Results from ALU is stored back in the registers and the sequence begins again Mentioned Moore s Law which you can look back at the lecture notes to read about You can increase CPU processing by o Pipelining o Us several independent paths and have CPU chip do the
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