Memory Organization
Memory Cell
Section titled “Memory Cell”Carries two stable states 1 and 0
Memory Types
Section titled “Memory Types”RAM (Random Access Memory)
Section titled “RAM (Random Access Memory)”Think of RAM as your computer’s “working desk” - it’s where active tasks happen.
Dynamic RAM (DRAM)
- Uses tiny capacitors (like mini batteries) that need constant refreshing
- Cheaper but slower
- Used for main memory in computers
Static RAM (SRAM)
- Uses flip-flop circuits (more stable)
- Faster but more expensive
- Used for cache memory (super-fast temporary storage)
ROM (Read-Only Memory)
Section titled “ROM (Read-Only Memory)”Like a book that’s already written - you can read it but can’t easily change it.
Types of ROM:
- PROM - Programmable ROM (can be written once)
- EPROM - Erasable PROM (can be erased with UV light)
- EEPROM - Electrically Erasable PROM
- Flash - Modern version used in USB drives and SSDs
| Memory Type | Category | Erasure | Write Mechanism | Volatility |
|---|---|---|---|---|
| Random-access memory (RAM) | Read-write memory | Electrically, byte-level | Electrically | Volatile |
| Read-only memory (ROM) | Read-only memory | Not possible | Masks | Nonvolatile |
| Programmable ROM (PROM) | Read-only memory | Not possible | Electrically | Nonvolatile |
| Erasable PROM (EPROM) | Read-mostly memory | UV light, chip-level | Electrically | Nonvolatile |
| Electrically Erasable PROM (EEPROM) | Read-mostly memory | Electrically, byte-level | Electrically | Nonvolatile |
| Flash memory | Read-mostly memory | Electrically, block-level | Electrically | Nonvolatile |
Memory Modules
Section titled “Memory Modules”A memory module is like a team of memory chips working together. Instead of using one huge chip, manufacturers combine smaller chips to create the memory size they need.
Example: Building a 256K×8bit Module
Section titled “Example: Building a 256K×8bit Module”- Goal: Create memory that stores 256,000 words, each 8 bits long
- Available: 256K×1bit chips (each stores one bit per word)
- Solution: Use 8 chips (one for each bit position)
- Result: When you read one address, you get 8 bits (one from each chip)
Larger Example: 1M×8bit Module
Section titled “Larger Example: 1M×8bit Module”- Goal: 1 million words of 8 bits each
- Available: 256K×1bit chips
- Math: Need 4 chips for capacity (4 × 256K = 1M) and 8 chips for width
- Total: 32 chips arranged in a 4×8 grid