What is ROM ? Why it is important?

CONTENTS OF PRESENTATION

• ROM (Mask Programmable ROM—also called “MROMs”)
• EPROM (UV Erasable Programmable ROM)
• OTP (One Time Programmable EPROM)
• EEPROM (Electrically Erasable and Programmable ROM)
• Flash Memory

Introduction 

READ-ONLY MEMORY (ROM), ALSO KNOWN AS FIRMWARE, IS AN 

INTEGRATED CIRCUIT PROGRAMMED WITH SPECIFIC DATA WHEN IT 

IS MANUFACTURED. ROM CHIPS ARE USED IN 

COMPUTERS,

IN THIS SECTION, YOU WILL LEARN ABOUT THE DIFFERENT TYPES OF 

ROM AND HOW EACH WORKS. 

ROM Types

 There are five basic ROM types: ROM, PROM, EPROM, EEPROM, Flash 

memory.

Although each type has its own set of characteristics, all memory two things are the same: •Data stored in these chips is nonvolatile -- it is not lost when power is

 removed.

 • The data that is stored in these chips cannot be altered or requires a special operation to change (in contrast to RAM, which can be changed just as easily) read).

This means that removing the power source from the chip will not cause it to 

lose any data.

ERASABLE PROGRAMMABLE READ 

ONLY MEMORY (EPROM)

• EPROM (UV Erasable Programmable Read Only Memory) is a 

special type of ROM that is programmed electrically and yet 

is erasable under UV light.

• • Programming an EPROM device requires forcing an electrical charge on a small piece of polysilicon material (called the

 floating gate) located in the memory cell.

 • The cell is inactive when this charge is present on this gate. "programmed," typically represented by a logic "0," and when this charge is it is a logic "1" that is not present.

REPROGRAMMING PROCESS OF EPROM

• Prior to being programmed, an EPROM has to be erased. To 

the EPROM is erased because it is exposed to ultraviolet light for approximately twenty minutes through its quartz window ceramic container • After erasure, new information can be programmed to the

 EPROM.

 • After the data have been written to the EPROM, an opaque label needs to be placed over the quartz window to prevent accidental ensure 

• Most EPROM chips exceeds 1000 cycle.

OTP (ONE TIME PROGRAMMABLE) 

EPROM

• • EPROMs are typically programmed once in most applications and will never need to be wiped out.

 • EPROMs may be used in these applications to cut costs. since the standard, sold in opaque plastic packages. An EPROM's ceramic package is pricey.

 • EPROMs, which are once-programmed for a specific purpose, and One-Time Programmables are those that cannot be erased. (OTP) devices.

EEPROM (ELECTRICALLY ERASABLE AND 

PROGRAMMABLE ROM)

• (EEPROM) is based on a semiconductor structure that is comparable to EPROM.

 • The entirety of its contents (or particular banks) to be electrically erased, and then electrically rewritten. • An EEPROM is much slower to write to or flash (in milliseconds). per bit) than reading from a ROM or writing to a RAM

 (in both instances, nanoseconds)

MASK ROM 

• What is mask ROM?

• A type of read-only memory known as mask ROM (MROM)

whose contents are programmed by the integrated circuit 

manufacturer (rather than by the user). The terminology 

"mask" comes from integrated circuit fabrication, where 

During the process of, portions of the chip are masked off. photolithography.

FLASH MEMORY(FLASH ROM)

• A contemporary form of EEPROM is flash memory, also known as flash. established in 1984. Compared to conventional EEPROM, flash memory can be written to and erased more quickly, and more recent designs feature extremely high endurance (more than one million cycles).  NAND flash today uses silicon chip area effectively, resulting in individual integrated circuits with a capacity as high as 16GBas of 2007[update]; this feature,

 NAND's endurance and physical durability have enabled it to replace magnetic drives in some applications (such as USB flash). Other names for flash memory include flash ROM and flash memory. EEPROM in place of older types of ROM, but not in applications that make use of its modification capabilities.