Programmable ROM facts for kids
A programmable read-only memory (PROM) is a special type of computer memory. You can write information onto a PROM chip only once after it's made. Once the data is written, it becomes permanent and cannot be changed. Think of it like a CD-R disc that you can record on just one time.
PROMs are a kind of read-only memory (ROM). They are used in many digital devices to store important, permanent information. This often includes basic programs called firmware or microcode, which help devices start up and work.
The main difference between a regular ROM and a PROM is when the data is added. Data is put onto a ROM chip during its manufacturing process. But for a PROM, the data is added *after* the chip has been manufactured. This makes PROMs useful for smaller production runs or when a system is still being developed.
Blank PROM chips are programmed using a special machine called a PROM programmer. Companies can buy blank PROMs and then program them with the specific data they need at the last minute. You can find PROMs in many devices around you. They are used in microcontrollers, video game consoles, mobile phones, and even in RFID tags. They are also found in medical devices, HDMI cables, and many car electronics.
History of PROMs
The PROM was invented in 1956 by a person named Wen Tsing Chow. He worked for the Arma Division of the American Bosch Arma Corporation in Garden City, New York.
The United States Air Force asked for this invention. They needed a more flexible and secure way to store targeting information for their Atlas E/F ICBM missiles. The technology was kept secret for several years because of its importance to the military.
The word burn, which means to program a PROM, comes from the original invention. One early method literally "burned" tiny internal wires inside the chip with too much electricity. This created a permanent break in the circuit. The first machines to program PROMs were also developed by Arma engineers under Chow's guidance.
One-Time Programmable Memory
OTP stands for One-Time Programmable memory. It's a special kind of non-volatile memory (NVM). "Non-volatile" means it keeps its data even when the power is turned off.
Like PROMs, OTP memory allows data to be written only once. After it's programmed, the information stays there forever. OTP memory is used where data needs to be read reliably over and over again.
Some examples of what OTP memory stores include:
- Boot code: The instructions a device needs to start up.
- Encryption keys: Secret codes used to protect information.
- Configuration settings: Important settings for how a device works.
OTP memory is popular because it uses little power and takes up a small space on a chip. This makes it useful in many products. You can find it in microprocessors, display drivers, and power management chips.
Early forms of OTP memory have existed since 1969. Texas Instruments developed a type in 1979. In 2001, Kilopass Technology Inc. patented new ways to make OTP memory using standard CMOS technology. This made it easier to include OTP memory directly into other computer chips.
Another type of one-time programmable memory uses the same chip as an ultraviolet-erasable programmable read-only memory (UV-EPROM). However, these chips are put into a dark, opaque package. UV-EPROMs usually come in expensive packages with a clear window so they can be erased with UV light. By using a dark package, these one-time programmable versions are cheaper to make. They are programmed in the same way as UV EPROMs.
How PROMs Are Programmed
A typical PROM chip starts with all its memory bits set to "1". When you program a PROM, you "burn" certain tiny fuses inside the chip. This burning process causes those specific bits to change from "1" to "0". This change is permanent and cannot be undone.
Imagine tiny electrical fuses inside the chip. When you program a bit, you send a strong electrical pulse through that fuse. This pulse is much stronger than what the chip normally uses. It breaks down a thin insulating layer, creating a permanent connection. This connection changes the bit's value from a "1" to a "0".
Some older computer processors, like the 6502, could use this feature. If there was a mistake in a program stored on a PROM, engineers could "reprogram" the incorrect instruction. They would change it to a special "break" instruction (which had a value of '00'). This would make the computer jump to a different part of the memory. There, a corrected set of instructions could be stored, allowing the program to work properly.
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