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Read Only Memory (ROM) chips, located on
the motherboard, contain instructions that can be directly accessed by
the microprocessor. Unlike RAM, ROM chips retain their contents even
when the computer is powered down. Their contents cannot be erased or
changed by normal means. Data transfer from ROM is faster than any
disk, but slower than RAM. Some examples of ROM chips that can be found
on the motherboard include BIOS ROM, EEPROM, and Flash ROM.
Basic Input/Output System (BIOS)
The instructions and data in the ROM chip that control the boot
process and the computer hardware are known as the Basic Input/Output
System (BIOS), sometimes called firmware. The ROM chip that contains
the firmware is called the ROM BIOS chip, or simply BIOS, and is
usually marked "BIOS" on the motherboard. The system BIOS is a very
critical part of the computer. In fact, if the CPU is considered the
brains of the computer, the system BIOS is considered the heart of the
system. It determines what hard drive is installed, whether there is a
3.5-inch floppy drive, what kind of memory is installed, and many
other important parts of the system hardware at startup. The
responsibility of the BIOS is to serve as a liaison between the
computer operating software and the various hardware components that
support it. These responsibilities are listed in Figure
 .
The BIOS is easy to locate because it is larger than most other
chips, and it often has a shiny plastic label containing the
manufacturer name, the serial number of the chip, and the date the
chip was manufactured. This information is vital when the time comes to select the correct
upgrade for the chip. The unique role the BIOS plays in the computer's
functionality is described in Chapter 3, "Assembling Your First
Computer".
EPROM, EEPROM, and Flash ROM
- EPROM and EEPROM are ROM chips that can be erased and
reprogrammed. Erasable Programmable Read-Only Memory (EPROM)
is a special type of Programmable Read-Only Memory (PROM)
that can be erased by shining ultraviolet light through a clear
window on top of the chip. Because the ROM chip holds the
instructions that enable a device to function properly, it sometimes
has to be reprogrammed or replaced when upgraded device
instructions are required. Unlike EPROM, Electrically Erasable Programmable Memory (EEPROM) chips are erased using a
higher than normal electric voltage instead of ultraviolet light.
When the system BIOS (or firmware) is contained on EEPROM, it can
be upgraded (reprogrammed) by running special instructions.
- Flash ROM are Special EEPROM chips that have been developed
as a result of advancements in EEPROM technology. Flash ROM holds
the firmware, or BIOS, in most new systems. It can be reprogrammed
under special software control. Upgrading BIOS by running special
software is known as flashing. The BIOS implemented on a flash
memory is known as plug-and-play BIOS, and it supports
plug-and-play devices. These chips retain data when the computer
is powered down so information is permanently stored.
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Lab
Activity (PDF, 10 KB) |
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In this lab,
students will be able to locate and identify the
ROM chip, BIOS, and BIOS manufacturer on the
motherboard. |
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