PC Start-up Procedure and Timing Lesson 6

 Hand in assignment from yesterday.  Describe the two main computer buses.  Describe how cache memory works.

 Identify the purpose of BIOS.  Describe the steps involved in booting a computer.  Define CMOS and its purpose.  Explain the system clock and Hertz.

 First instruction from the BIOS (Basic Input/Output System)  Part of the EPROM ( Erasable Programmable Read-Only Memory ).  BIOS loads the operating system  Takes over and “drives” the microprocessor

 Manages the dataflow between the computer's Operating System and attached devices  Hard disk, video adapter, keyboard, mouse, printer, etc.

 An integral part of your computer  Installed at the factory  Microprocessor passes control to the BIOS program, which is always located at the same place on EPROM

 Comprises several separate routines, serving different functions  Inspects the computer to determine what hardware is fitted (attached)  Conducts some simple tests to check that everything is functioning normally  POST (Power On Self Test)

 If all tests are passed the EPROM tries to boot the machine from the hard disk  If fails, it will try the CD-ROM drive, then the floppy drive,  Displays a message that it needs a system disk

 BIOS loads the OS (or parts of it) into RAM from hard disk  With BIOS, the OS and its applications are freed from having to understand exact details about the attached input/output devices  BIOS is the intermediary between the microprocessor and I/O device

 CMOS (Complementary Metal Oxide Silicon) RAM chips  Kept “alive” by a battery  Stores basic information about the PC’s configuration ◦ # and type of hard and floppy drives, how much memory, what kind, etc. ◦ All this used to be entered manually, but modern BIOS does this work

Video

 CMOS RAM Also stores the time and date  Updated by a Real Time Clock (RTC)  The clock, CMOS RAM and battery are usually all integrated into a single chip. The PC reads the time from the RTC when it boots up, after which the CPU keeps time – which is why system clocks are sometimes out of sync. Rebooting the PC causes the RTC to be reread, increasing their accuracy.

 Every PC has a system clock  Keeping time of day is not the clock’s primary purpose  Clock is driven be a quartz crystal  When electricity is applied, the molecules in the crystal vibrate  PC uses the vibrations of the quartz to time its processing operations

 Computer’s operating speed is tied to the speed of the system clock  800 MHz = “ticks” 800 million times per second  Clock cycle is a single tick, or the time it takes to turn a transistor off and back on again  Processor can execute an instruction in a given number of clock cycles  As clock speed increases, so does the number of instructions it can carry out each second

 A Hertz is a single oscillation (up and down movement) of an electromagnetic wave  Mega means millions of wave oscillations per second  A 200 MHz chip has a clock that receives electricity and switches on and off 200 million times per second.  PC’s overall speed depends not only on the speed of the CPU but also on its bus

 1 Hz = one cycle/second  1 MHz = one million/second  1 GHz = one billion/second  Heindrich Hertz: physicist who first detected electromagnetic waves in 1883

 Work on your projects with your partner.  Due the end of today’s block! Directions