Transcript ROM: Read Only Memory

ROM: Read Only Memory
is an integrated circuit
programmed with specific data
when it is manufactured
‫هي عبارة عن دائرة اليكترونية متكاملة برمجت‬
.‫عند صناعتها ضمن بيانات خاصة‬
‫‪ROM Types‬‬
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‫ذاكرة القراءة فقط ‪ROM‬‬
‫ذاكرة القراءة فقط القابلة للبرمجة ‪PROM‬‬
‫ذاكرة القراءة فقط القابلة للبرمجة والمسح ‪EPROM‬‬
‫ذاكرة القراءة فقط القابلة للبرمجة والمسح ‪EEPROM‬‬
‫االليكتروني‬
‫ذاكرة الوميض ‪• Flash memory‬‬
Characteristics of ROM Types
• Data stored in these chips is nonvolatile,
it is not lost when power is removed.
• Data stored in these chips is either
unchangeable or requires a special
operation to change (unlike RAM, which
can be changed as easily as it is read).
ROM at Work
ROM uses a diode to connect the lines if the value is 1. If the value is 0, then
the lines are not connected at all.
Standard ROM
• ROM uses a diode to connect the lines if the
value is 1. If the value is 0, then the lines are not
connected at all.
• You cannot reprogram or rewrite a standard
ROM chip. If it is incorrect, or the data needs to
be updated, you have to throw it away and start
over
• Creating ROM chips totally from scratch is timeconsuming and very expensive in small
quantities
PROM programmable readonly memory
• Blank PROM chips can be bought inexpensively
and coded by anyone with a special tool called a
programmer.
• that every intersection of a column and row in a
PROM chip has a fuse connecting them
• The higher voltage breaks the connection
between the column and row by burning out the
fuse. This process is known as burning the
PROM.
EPROM Erasable programmable
read-only memory
• EPROM chips can be rewritten many times.
• Erasing an EPROM requires a special tool that
emits a certain frequency of ultraviolet (UV) light.
• Once again we have a grid of columns and rows.
In an EPROM, the cell at each intersection has
two transistors.
• One of the transistors is known as the floating
gate and the other as the control gate.
• To erase it, you must supply a level of
energy strong enough to break through the
negative electrons blocking the floating
gate
• . In a standard EPROM, this is best
accomplished with UV light at a frequency
of 253.7
• The EPROM must be very close to the
eraser's light source, within an inch or two,
to work properly.
EEPROM Electrically erasable
programmable read-only memory
• remove the biggest drawbacks of EPROMs.
• The chip does not have to removed to be
rewritten.
• The entire chip does not have to be completely
erased to change a specific portion of it.
• Changing the contents does not require
additional dedicated equipment.
• EEPROMs are changed 1 byte at a time ‫بطيئة‬
Flash Memory
• Flash memory works much faster than
traditional EEPROMs because it writes
data in chunks, usually 512 bytes in size,
instead of 1 byte at a time
• One of the most common uses of Flash
memory is for the basic input/output
system of your computer
BIOS
• BIOS is the third type of software your
computer needs to operate
successfully(1st operating System, 2nd
Applications).
• but its most important role is to load the
operating system
BIOS Tasks
• A power-on self-test (POST) for all of the different
hardware components in the system to make sure
everything is working properly
• Activating other BIOS chips on different cards installed in
the computer - For example, SCSI and graphics cards
often have their own BIOS chips.
• Providing a set of low-level routines that the operating
system uses to interface to different hardware devices It is these routines that give the BIOS its name. They
manage things like the keyboard, the screen, and the
serial and parallel ports, especially when the computer is
booting.
• Managing a collection of settings for the hard disks,
clock, etc.
When you turn on your
computer, the BIOS does several
things. This is its usual
sequence
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Check the CMOS Setup for custom settings
Load the interrupt handlers and device drivers
Initialize registers and power management
Perform the power-on self-test (POST)
Display system settings
Determine which devices are bootable
Initiate the bootstrap sequence
Updating Your BIOS
• the BIOS needs to change in order to understand the
new hardware
• Look at the BIOS revision and date information displayed
on system startup
• Then go to the BIOS manufacturer's Web site to see if
an upgrade is available
• Download the upgrade and the utility program needed to
install it
• Copy the program onto a floppy disk
• Restart your computer with the floppy disk in the drive,
and the program erases the old BIOS and writes the new
one
Major BIOS manufacturers
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American Megatrends Inc. (AMI)
Phoenix Technologies
ALi
Winbond