Computer Memory
Primary Storage
Primary storage refers to the memory that the CPU can access directly and quickly. Unlike secondary storage (HDDs/SSDs), primary memory is essential for the Fetch-Execute cycle to function.
Primary storage refers to the memory that the CPU can access directly and quickly. Unlike secondary storage (HDDs/SSDs), primary memory is essential for the Fetch-Execute cycle to function.
At A-Level, you must distinguish between the two main types of primary storage based on their volatility and purpose.
| Feature | RAM (Random Access Memory) | ROM (Read Only Memory) |
|---|---|---|
| Volatility | Volatile (Contents lost when power is off) | Non-Volatile (Contents retained) |
| Read/Write | Read and Write enabled | Read-only (usually) |
| Typical Size | Large (e.g., 8GB - 32GB) | Small (e.g., a few MBs) |
| Contents | Operating System, running programs, and data | The Bootstrap loader (BIOS/UEFI) |
When RAM becomes full, the Operating System allocates a portion of the Secondary Storage (Hard Drive/SSD) to act as temporary RAM. This is known as Virtual Memory.
Flash memory is a type of non-volatile memory that can be electrically erased and reprogrammed. It uses NAND gate technology and is commonly found in SSDs, USB drives, and SD cards.
In 2026, NVMe SSDs have largely replaced traditional SATA drives in performance-critical systems due to their direct connection to the PCIe bus, drastically reducing latency.