Chapter 4 The Components of the System UnitThe System Unit- Box-like case that contains computer’s electronic components - Sometimes called the chassisWhat are common components inside the system unit?- Processor- Memory module- Expansion cardso Sound cardo Modem cardo Video cardo Network interface card- Ports and ConnectorsWhat is the motherboard?- Main circuit board in system unit- Contains chips, integrated circuits, and transistors- Also called system boardWhat chip packages are available?- single edge contact (SEC) cartridge- dual inline package (DIP)- flip chip-PGA (FC-PGA) package- pin grid array (PGACentral Processing UnitWhat is the central processing unit (CPU) ?- Interprets and carries out basic instructions that operate a computer- Also called the processorWhat are the components of the CPU?- Control Unit- Arithmetic/Logic Unit (ALU)What is the control unit?- Directs and coordinates operations in computer- Control unit repeats four basic operations:1- Fetch - obtain program instruction or data item from memory- Decode - translate instruction into commands- Execute - carry out command- Store - write result to memoryWhat is a machine cycle?- Four operations of the CPU comprise a machine cycle- Also called instruction cycle- Instruction time (i-time) - time taken to fetch and decode- Execution time (e-time) - time taken to execute and storeAn example of a machine cycle- Student enters math problem (100 x 52) into computer’s memory- Result in memory displays on monitor’s screenHow is the CPU’s speed measured?- According to how many millions of instructions per second (MIPS) it can processWhat are two designs used for the CPU?- CISC (complex instruction set computing)o Supports large number of instructionso CPU executes complex instructions more quickly- RISC (reduced instruction set computing)o Supports smaller number of instructionso CPU executes simple instructions more quicklyWhat is the arithmetic/logic unit (ALU) ?- CPU component that performs execution part of the machine cycleo Arithmetic (addition, subtraction, multiplication, and division)o Comparison (greater than, equal to, or less than)o Logical (AND, OR, NOT)What is pipelining?- CPU begins executing second instruction before completing first instruction- Results in faster processingWhat is a register?- Temporary storage area that holds data and instructionso Stores location from where instruction was fetchedo Stores instruction while it is being decoded2o Stores data while ALU processes ito Stores results of calculationWhat is the system clock?- Synchronizes all computer operations- Each tick is clock cycle- MHz megahertz (millions)- GHz gigahertz (billions)What is a microprocessor?- Single processor chip found in personal computersHow do personal computer processors compare?- Intel - PC- AMD - PC- Motorola - MacWhat is a coprocessor?- Chip that assists processor in performing specific tasks- One type is a floating-point coprocessor, also known as a math or numeric coprocessorWhat is parallel processing?Using multiple processors simultaneously to execute program fasterRequires special software to divide problem and bring results togetherData RepresentationHow do computers represent data?- Most computers are digital- Recognize only two discrete states: on or offWhat is the binary system?- Number system with two unique digits: 0 and 1What is a byte?- Eight bits grouped together- 256 charactersWhat are three popular coding systems to represent data?- ASCII - American Standard Code for Information Interchange- EBCDIC - Extended Binary Coded Decimal Interchange Code- Unicode - coding scheme capable of representing all world’s languagesHow is a character sent from keyboard to computer?- Step 1: Press letter T3- Step 2: Electronic signal for letter T sent to system unit- Step 3: Signal changed to its ASCII code (01010100) and stored in memory- Step 4: After processing, binary code for letter T is converted to image on output deviceMemoryWhat is memory?- Temporary storage area for operating system, application programs, and data - Consists of one or more chips on motherboard- Each byte stored in unique addressHow is memory measured?- By number of bytes availableo KBo MBo GBo TBWhat are two types of system unit memory?- volatile memoryo Loses its contents when computer's poweris turned off- nonvolatile memoryo Does NOT lose its contents when computer’s power is turned offWhat is random access memory (RAM)?- Memory chips that can be read from and written to by processor- Most RAM is volatile- The more RAM a computer has, the faster it operatesWhat are two basic types of RAM chips?- Dynamic RAM (DRAM)o Most common typeo Also called main memory- Static RAM (SRAM)o Used for special applications such as cacheo Faster and more reliable than DRAM chipsHow much RAM is needed?- Software package usually indicates RAM requirements4How much RAM is needed?- Depends on type of applications you intend to run on your computerWhat is cache- Helps speed computer processes by storing frequently used instructions and data- Also called memory cache, cache store, or RAM cache- L1 cache built in processor- L2 and L3 cache not built in processor - L2 advanced transfer cache most commonWhat is read-only memory (ROM)?- Memory chips that contain data, instructions, or information that is recorded permanently- Data can only be read; cannot be modified in ROM- ROM is nonvolatile — Contents not lost when computer is turned offo BIOS (basic input/output system)o Stored on ROM- Sequence of instructions computer follows to load operating system and other files when you turn on the computerTypes of ROM - Firmware- ROM chips manufactured with permanently written data, instructions, or information- PROM (programmable read-only memory)o Blank ROM on which you can place items permanently- EEPROM (electrically erasable programmable read-only memory)o Type of PROM containing microcode programmer can eraseWhat is flash memory?- Nonvolatile memory that can be erased electronically and reprogrammed- Used with handheld computers and digital cameras, cellular phones, and automobileWhat is CMOS?- Complementary metal-oxide semiconductor memory- Stores information about the computero type of disk driveso keyboardo monitoro current time and date5- Uses battery to retain information when computer is turned offWhat is memory access time?- Speed at which processor can access data from memory directly- Measured in