Computers Inside and Out Dr Jim Martin jim.martin@cs.clemson.edu copyright Jim Martin 2006

Basics External computer parts Internal Computer parts copyright Jim Martin 2006

Components inside the system unit power supply ports drive bays processor memory sound card video card Processor Memory Adapter cards Sound card Video card Ports Drive bays Power supply copyright Jim Martin 2006

The motherboard Main circuit board in system unit Contains adapter cards, processor chips, and memory chips Also called system board copyright Jim Martin 2006

CPU: Central Processing Unit Processor Control Unit Arithmetic Logic Unit (ALU) Control Unit Arithmetic Logic Unit (ALU) Interprets and carries out basic instructions that operate a computer Instructions Data Information Control unit directs and coordinates operations in computer Memory Input Devices Data Information Output Devices Arithmetic logic unit (ALU) performs arithmetic, comparison, and logical operations Instructions Data Information Also called the processor Storage Devices copyright Jim Martin 2006

Machine Cycle Four operations of the CPU comprise a machine cycle Step 1. Fetch Obtain program instruction or data item from memory Processor Control Unit Memory ALU Step 2. Decode Translate instruction into commands Step 4. Store Write result to memory Step 3. Execute Carry out command copyright Jim Martin 2006

Each tick is a clock cycle Pace of system clock is clock speed Controls timing of all computer operations Generates regular electronic pulses, or ticks, that set operating pace of components of system unit Each tick is a clock cycle Pace of system clock is clock speed Most clock speeds are in the gigahertz (GHz) range (1 GHz = one billion ticks of system clock per second) Processor speed can also be measured in millions of instructions per second (MIPS) copyright Jim Martin 2006

Which Processor ? Celeron Itanium or Xeon Pentium family 1.3 GHz and up 3.0 GHz and up 2.4 GHz to 3.0 GHz Up to 2.4 GHz 2.2 GHz and up Intel Processor Desired Clock Speed The faster the processor, the more expensive the computer The faster the processor, the more electricity consumers….this is why processors for laptops run at slower system clock speeds copyright Jim Martin 2006

Data Representation Computers are digital which means: Recognize only two discrete states: on or off Use a binary system to recognize two states Use Number system with two unique digits: 0 and 1, called bits (short for binary digits) copyright Jim Martin 2006

Bits/Bytes Computers speak in terms of 1’s and 0’s (i.e., in binary!!!) When one computer sends the message ‘Hello’ to another computer, each of the 5 characters is represented as a sequence of 8 bits A bit is a single 1 or 0 A byte is a sequence of bits- usually 8 The message ‘Hello’ is stored on the computer in 5 bytes Characters (e.g., “A”) are mapped to unique sequences of 8 bits This mapping is defined by a standard known as ASCII copyright Jim Martin 2006

Binary number system In a base-10 number system, the values of each digit range from 0 … 9. But the magnitude of each digit is a multiple of 10: (the 1’s column, the 10’s column, 100, 1000… ) the pattern: 10EXP(column #) E.g., the decimal number 1023 : 1*1000 + 0*100 + 2*10 + 3*1 = 1023 Binary numbers are a number system made up of 0's and 1's Each digit can only be a 0 or 1. The magnitude of each column is 2EXP(column #) The values of the first 8 places in binary notation are (highest to lowest): Bit# 7 6 5 4 3 2 1 0 128 64 32 16 8 4 2 1 We show several numbers in binary (with 8 bits or digits) and in decimal 00000010 = 2 in decimal 00000100 = 8 in decimal 10000010 = 130 in decimal 11111111 = 255 in decimal How would you write the number 3 in binary? copyright Jim Martin 2006

Homework for next time Complete the 3 worksheets copyright Jim Martin 2006