This document discusses PC hardware components including ROM, BIOS, CMOS, and the boot process. It provides details on: 1) ROM is read-only memory that permanently stores low-level programs like BIOS. BIOS contains small programs that enable the CPU to communicate with devices. 2) CMOS is a separate memory chip that stores configurable data about changeable hardware, like RAM and hard drives. It is accessed via the CMOS setup program in BIOS. 3) When a PC boots, the POST program in BIOS runs self-tests, then the bootstrap loader searches boot devices like the hard drive to find and load the operating system.

1. 19-204-0307 Hardware Design Laboratory-
A: PC HARDWARE
CO-1: Familiarize, trouble shoot, maintenance and
Assembling a PC
 More on Mother boards
 Trouble shooting/maintenance/Assembling

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3. What is (ROM)?
 Read Only Memory
 Memory chips that contain data, instructions, or
information that is recorded permanently.
 Data can only be read, cannot be modified
 Nonvolatile — Contents not lost when the computer is
turned off
 Program stored on ROM are known as firmware not a
Software.

4. Read Only Memory (ROM)
 ROM have different type:ROM, PROM
 Programmable Read-Only Memory (only once)
 EPROM
 Erasable PROM by Ultraviolet
 EEPROM
 Electrically Erasable PROM
 A type of PROM containing microcode that a
programmer can erase using electricity.

5. What is Flash Memory?
 Variation of EEPROM
 Also called flash ROM or flash RAM
 Nonvolatile memory that can be erased electronically
and reprogrammed.
 Stores data and programs on many handheld
computers and devices such as Camera and mobile
phone.
 Flash memory cards
store flash memory on
removable devices
instead of chips

6. Basic Input Output Systems
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 A special kind of Program is required to enable the CPU
to talk to other devices
 These programs are collectively known as the basic
input/output service (BIOS)
 When CPU wants to talk to KB controller, it goes to BIOS
ROM chip to access the proper program.
Similar to
codebook

7. BIOS
 Basic Input Output Systems
 Permanently stored on ROM chip called System ROM or
System BIOS
 Contains small programs - each program is called a
service- that enable CPU to
 Communicate with the devices (keyboard, hard drive,
monitor, …)
 They are necessary to start the computer
 load the operating system
 and other files when you first turn on the computer
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9. ROM BIOS
 There is One ROM chip on the system board that contains
BIOS.
 Modern motherboards use Flash ROM (you can change the
contents through a very specific process called “flashing the
ROM”)
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10. System BIOS
 Every system BIOS has two types of hardware to support.
 First:
 All hardware that never changes.
 Ex: KB, PC speaker.
 You cannot change keyboard controller chip.
 Second:
 All hardware that might change.
 Ex: RAM (you could add RAM), hard drives (replacing/ adding).
 The system ROM stores the BIOS for them, but it needs another
place to store information about the specific details of them
CMOS
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11. CMOS
 A separate memory chip, called Complementary Metal-
Oxide Semiconductor (CMOS) chip stores the
information that describes specific device parameters.
 CMOS does not store programs, only data that is read by
BIOS to be able to talk to the changeable hardware.
 CMOS also acts as a clock to keep date and time
 Years ago: CMOS was in separate chip.
 Today: CMOS is built into Southbridge.
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12. CMOS
 CMOS can store up to 64KB of data but usually only
uses about 128 bytes
 CMOS chip is volatile (kept alive by battery). This
way the information contained in the CMOS are
always present even if the computer power is
turned off.
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13. CMOS
 Stores only changeable data.
 Customizable via SETUP program.
 If data in CMOS about certain hardware is different
from its actual specs, PC can not access that
hardware.
 If you change one of changeable devices,
parameters have to be changed in CMOS  how to
change data on CMOS?
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14. CMOS SETUP Program
 Special program that allows you to access and update
CMOS data
 Stored on system ROM (BIOS)
 Companies that write the BIOS and how to access
CMOS at boot:
 Phoenix Technologies - Ctrl Alt Esc
 Award Software - uses DEL key
 American Megatrends (AMI) - DEL key
 Other key combinations are: Ctrl Alt Ins, Ctrl A, Ctrl S,
Ctrl F1, or F10
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15. Accessing Award SETUP
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16. CMOS setup program
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17. Device drivers-(Windows)
 A device driver is a file that contains the BIOS commands
necessary to communicate with the devices they support
.
 Operating system loads these drivers into RAM when
booting
 They come with the device - in a CD- when you buy it.
 The generic name for CD is installation disc
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18. POST
 The power-on self test (POST) is a special program stored
on the ROM chip (BIOS)
 Initiated when the computer is turned on or is reset
 Checks out the system every time the computer boots
 POST program sends out a standard command that says
to all the devices “check yourselves out”.
 PCs convey POST information to user in two ways:
 beep codes
 or text message
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19. System ROM Responsibility
 System ROM contains:
 BIOS routines
 CMOS setup program
 POST
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20. (Booting -Steps)
Once the power is turned on, the PC “pulls itself up by its
bootstraps”
 First component to wake up is the CPU.
 By reads a special wire called power good wire once the
power supply provides the certain voltage to the CPU
 Built in memory address is sent on address bus.This
address represent the first line of POST program on the
system ROM
 POST is run-If problem happen beep code or text message
displayed.
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21. Boot Process
 After POST finishes, it passes control to last BIOS
function: the bootstrap loader. Its job is to find the
operating system.
 The bootstrap loader loads the operating system from
the boot sector
 Search for the hard drive
 Boot order set in CMOS

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22. Boot Process
 If the device is bootable (called system disk), its boot
sector will contain special programming designed to
tell the system where to locate the operating system.
 If bootstrap loader locates a good boot sector, it passes
control to operating system and removes itself from
memory.
 Otherwise it goes to next device specified in CMOS.
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