semiconductor memory

**Semiconductor Memory** — integrated circuits designed to store digital data, categorized by volatility and access method. **Volatile Memory (Loses Data Without Power)** - **SRAM (Static RAM)**: 6 transistors per bit. Very fast, no refresh needed. Used for CPU caches (L1/L2/L3). Expensive, low density - **DRAM (Dynamic RAM)**: 1 transistor + 1 capacitor per bit. Needs periodic refresh (~64ms). Main system memory (DDR4/DDR5/HBM). High density, moderate speed **Non-Volatile Memory (Retains Data)** - **NAND Flash**: Floating-gate or charge-trap transistors. Used in SSDs, USB drives, smartphones. Types: SLC (1 bit/cell), MLC (2), TLC (3), QLC (4) - **NOR Flash**: Random access reads for code storage. Used in embedded systems, BIOS - **Emerging**: MRAM (magnetic), ReRAM (resistive), PCM (phase-change). Aim to combine DRAM speed with flash non-volatility **Memory Hierarchy** - Registers → L1 Cache (SRAM) → L2/L3 → DRAM → SSD (NAND) → HDD - Each level: larger capacity, higher latency, lower cost per bit **HBM (High Bandwidth Memory)**: 3D-stacked DRAM with TSVs, providing massive bandwidth for GPUs and AI accelerators (H100: 3.35 TB/s).