💡 What is EPROM?
EPROM stands for Erasable Programmable Read-Only Memory.
It’s a type of non-volatile memory that:
⚡ Key Characteristics of EPROM:
| Feature | Description |
|---|---|
| 🔁 Programmable | ✅ Yes |
| ❌ Rewritable | ✅ Yes (but not instantly) |
| ⚡ Erasable | ✅ Yes, using ultraviolet (UV) light |
| 🔋 Volatile | ❌ No (retains data without power) |
| ⏱️ Rewrite cycles | Limited (typically a few hundred to thousands) |
🔍 How EPROM Works (Simplified):
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Internally, data is stored in transistors with floating gates.
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To program it, a special voltage is applied to store charges in these gates.
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To erase it, the EPROM chip is exposed to UV light for several minutes.
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It has a quartz window on top for this reason.
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UV light discharges the floating gates, erasing the chip.
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⚠️ Once erased, the entire chip is cleared—not selective erasing like in EEPROM.
🧪 EPROM Lifecycle:
[Blank chip] → Program → Use → Erase with UV → Reprogram → Repeat📦 Use Cases of EPROM:
| Use Case | Why EPROM? |
|---|---|
| 🔧 Embedded systems during development | Allows iterative programming during testing |
| 🧪 Prototype boards | Code can be changed if bugs are found |
| 🏭 Old BIOS chips | Reprogrammable but secure until exposed to UV |
| 💾 Device firmware | In older electronics, before EEPROM/flash became popular |
❌ Limitations of EPROM:
| Limitation | Impact |
|---|---|
| ☀️ UV erasing is slow | Takes ~10–20 minutes |
| ❎ Erases entire chip | No selective erase |
| 🔍 Needs special hardware | UV eraser, programmer |
| 👴 Obsolete | Replaced by faster, more flexible EEPROM and flash memory |
🧠 Interview-Ready Definition:
EPROM (Erasable Programmable Read-Only Memory) is a type of non-volatile memory that can be programmed electrically and erased using ultraviolet light. It allows multiple write cycles but requires full-chip erasure before rewriting, making it suitable for firmware development and older embedded systems.