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Microprocessor speeds • Measure of system clock speed – How many electronic pulses the clock produces per second (clock frequency) – Usually expressed in frequency (unit Hz) 1 Hz = 1 cycle / second • Kilohertz (KHz), Megahertz (MHz), Gigahertz (GHz) – Or how much time for each cycle: clock cycle time clock cycle time = 1 / clock frequency Second, millisecond, microsecond, nanosecond • Comparison of clock speed only meaningful between identical microprocessors 1 Other performance measures • Millions of Instructions per Second (MIPS) – High-speed personal computers can perform over 500 MIPS – Typically a more accurate measure of performance than clock speed • Megaflop: one million floating-point operations – Measures ability of computer to perform complex mathematical operations 2 Types of microprocessors • Microprocessor • Intel makes a family of processors – Pentium III and Pentium4 processors in most PCs – Celeron processor sold for low-cost PCs – Xeon and Itanium for high-end workstations and network servers • Other processors – AMD make Intel-compatible microprocessors – PowerPC chips used primarily in Macintosh computers – Compaq’s Alpha microprocessor used in high-end servers 3 Factors to CPU performance • Size of word Larger word mean more information can be processed by each instruction • Fast system frequency means more instructions can be done in a unit of time or equivalently short clock cycle time means each instruction can be done an short time • Small number of clock cycles for each instruction more instruction can be done in a unit time • Power consumption 4 Silicon technology • The size of a transistor – New technology makes the size of a transistor smaller and smaller! – Unit used to measure the size – Majority: 0.13 micro meter or 130 nano meter Moving to 0.09 micro meter or 90 nano meter Advanced: 65 nano meters Next a year: 45 nano meters Limit 10 nano meter? 5 Processor trends • The numbers of transistors in a CPU • Word size • Frequency • Number of processors on a chip • Voltage 6 Factors of system performance • CPU speed • Memory size • Front bus speed • Access speed to storage 7 Storage hierarchy • Register • Cache • Main memory • Secondary storage, such hard drive 8 Cache Memory • A temporary storage area Cache L2 – Speeds up data transfer within computer • Processor cache Cache L1 Control Unit Registers ALU CPU 9 Processor cache • A small block of high-speed memory – Stores most frequently and most recently used data and instructions • Microprocessor looks for what it needs in cache first – Transferred from cache much faster than from memory – If not in cache, control unit retrieves from memory • The more cache “hits” the faster the system performance • Internal (Level 1) cache built into microprocessor – Fastest access, but highest cost • External (Level 2) cache on separate chip – Incorporated into processor on some current microprocessors 10