Read Only Memory
- 1. READ ONLY MEMORY PRADEEP GUPTA
- 2. ROM (READ ONLY MEMORY) ROM is a class of storage media used in computers and other electronic devices. Data stored in ROM cannot be modified (at least not very quickly or easily). The ROM is non-volatile memory as it retains stored information even if the power is turned off (unlike RAM).
- 3. Processor uses ROM to store and execute programs instructions. It is mainly used to distribute firmware. Firmware is software that is very closely tied to specific hardware, and unlikely to require frequent updates. It is permanent memory in a computer that cannot be changed. Most memory is wiped clean when you turn off your computer. If it lost all memory it would not be able to start up again. So it needs some instructions stored in memory that is there when the computer starts. It then uses this to give further instructions to the computer and help it boot up.
- 5. READ ONLY MEMORY Read The word line is activated. The transistor is closed and the voltage on the bit line drops to near 0 if there is a connection between the transistor and the ground. If there is no connection to ground, the bit line remains high. Write Done when it is manufactured Bit line Word line •Not connected to store 1 •Connected to store 0 P
- 6. ROM INTERNAL STRUCTURE n X N decoder Memory array 2^N words X m bits n input lines m output lines/data lines Address lines
- 7. Size of ROM to implement full adder :-) Full adder X Y S =∑(1,2,4,7) Z C=∑(3,5,6,7) Address line= No. of variables=3 Data line= No. of functions to be implemented=2 CS ZYX A0 D1D0 A1 A2 Therefore, Size of ROM=2^3*2 Address location=2^3=8 2^3*2 ROM
- 8. Location A2 A1 A0 S C 0 0 0 0 0 0 1 0 0 1 1 0 2 0 1 0 1 0 3 0 1 1 0 1 4 1 0 0 1 0 5 1 0 1 0 1 6 1 1 0 0 1 7 1 1 1 1 1 ROM table What is the data stored in 4th location? Ans=10
- 9. APPLICATIONS A typical application of a ROM might be an industrial machine that repeats the same sequence over and over. ROM is used to store Basic Input-Output System (BIOS). Used extensively in embedded system. The boot up software for a regular PC, which performs the same task each time the power is turned on. ROMs are used in constructing look-up tables for computer systems. Look-up table are used to store logarithms of number, sines and cosines of angles, fixed physical constants and so on.
- 10. TYPES OF ROM Programmable read-only memory • Standard PROM can only be programmed once. • PROMs are manufactured blank. The data is programmed into them after manufacturing. • PROM chips are manufactured with a series of fuses. PROM chips have several different applications, including cell phones, video game consoles, RFID tags, medical devices, and other electronics.
- 11. Programmability is achieved by inserting a fuse at point P Memory contains all 0’s before programming. The user can insert 1’s at the required locations by burning out the fuses at these locations using high current pulses. This process is irreversible. Provides flexibility and convenience not available in ROM. Bit line Word line •Manufactured connected (storing 0), but the connection is a “fuse” and can be burned out with a high current to change it to 1. P(Fuse)
- 12. Erasable programmable read-only memory(EPROM) Content can be erased and reprogrammed. (EPROM) can be erased by exposure to strong ultraviolet light. EPROM chip packages can often be identified by the prominent quartz "window" which allows UV light to enter. Must be physically removed from the circuit for reprogramming. Entire content are erased.
- 13. Electrically erasable programmable read-only memory (EEPROM) Erased electrically. Need not be removed from the computer (or camera, MP3 player, etc.). Possible to erase the cell contents selectively. Disadvantages Different voltages are needed for erasing , writing and reading the stored data. Writing or flashing an EEPROM is much slower (milliseconds per bit) than reading from a ROM or writing to a RAM (nanoseconds in both cases).
- 14. Electrically alterable read-only memory(EAROM) Only 1 bit can be modified at a time. Writing is a very slow process and requires higher voltage (usually around 12 V) than is used for read access. EAROMs are intended for applications that require infrequent and only partial rewriting. EAROM is an expensive and complex technology. Most often used for industrial and military applications.
- 15. Flash memory Flash memory is a non volatile memory. They can be electrically erased and reprogrammed. It is an extension of EEPROM. It allows the stored data to be saved even when the device is disconnected from the power source. Writing speed is much faster than EEPROM. Data capacity is more. E.g. pen drives, solid state drives, memory cards, etc.
- 16. DISADVANTAGES ROMs however also have some disadvantages. It takes a long time to manufacture a ROM. The unit price of a ROM is quite high. Once the ROM has been manufactured and if some error has been discovered in the information store you can’t change the contents. This means that making mistakes are very expensive.
- 17. REFERENCES Computer Architecture And Organization JOHN P. HAYES http://www.google.co.in http://www.worldofcomputing.net/memory/read- only-memory.html https://www.slideshare.net/rohitladdu/romread-only- memory http://www.homes.ieu.edu.tr/leren/ce302/lectures/R OM%20(Read%20Only%20Memory)
- 18. THANK YOU