Erasable Programmable Read-Only Memory (EPROM)
Erasable-Programmable-Read-Only-Memory (EPROM) is a type of non-volatile memory used in computers and other electronic devices for storing data or program code that needs to be read but not frequently modified. Here's a detailed overview:
History and Development
- EPROM was developed in the late 1960s by Dov Frohman, who was working at Intel Corporation at the time.
- The first EPROM chip, the Intel 1702, was introduced in 1971, offering 2048 bits of storage.
Functionality
- EPROM can be erased and reprogrammed multiple times, which is a significant advancement over its predecessor, the ROM (Read-Only Memory), which could not be altered after manufacturing.
- Erasing is achieved by exposing the chip to ultraviolet light through a quartz window in the package, which resets all bits to '1'.
- Programming is done by applying a higher voltage than the standard operating voltage to write '0's into specific memory locations.
Physical Characteristics
- EPROM chips typically have a transparent quartz window on top, which allows UV light to penetrate and erase the memory content.
- The window is usually covered with an opaque label when not in use to prevent accidental erasure.
Programming Process
- Programming EPROMs involves using specialized EPROM programmers or devices that can apply the correct voltage and timing to write data into the chip.
- Once programmed, the data remains stored even when power is removed, making EPROM a form of non-volatile memory.
Erasure
- To erase an EPROM, it must be removed from the circuit and exposed to UV light for about 10 to 30 minutes, depending on the light's intensity.
- Full erasure is confirmed when all memory cells are reset to their initial state, typically all '1's.
Applications
- EPROMs were used extensively in early computer systems for storing firmware like BIOS.
- They were also used in arcade games, satellite systems, and any application where the code might need occasional updates or modifications.
Advantages and Limitations
- Advantages: Reusability, the ability to change firmware without hardware replacement, and the ease of testing and debugging by reprogramming.
- Limitations: The need for physical removal for erasure, slow erasure process, and the potential for damage due to UV exposure or static electricity.
Evolution and Successors
- EPROMs have largely been replaced by EEPROM (Electrically Erasable Programmable Read-Only Memory) and Flash Memory, which offer electrical erasing and reprogramming without UV light and with much faster erase times.
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