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 صناعتهاضمن بيانات خاصة.

ROM Types • ROM ذاكرة القراءة فقط • PROM ذاكرة القراءة فقط القابلة للبرمجة • EPROM ذاكرة القراءة فقط القابلة للبرمجة والمسح • EEPROM ذاكرة القراءة فقط القابلة للبرمجة والمسح الاليكتروني • Flash memory ذاكرة الوميض

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 time-consuming and very expensive in small quantities

PROM programmable read-only 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 timeبطيئة

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 • 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 • American Megatrends Inc. (AMI) • Phoenix Technologies • ALi • Winbond

ROM: Read Only Memory