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 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).RAM

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.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 253.7UV light 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 timeبطيئةbyte

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 computerFlash memory

BIOS BIOS is the third type of software your computer needs to operate successfully(1 st operating System, 2 nd 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.SCSI 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.keyboardscreen serialparallel ports Managing a collection of settings for the hard disks, clock, etc.hard disks

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