Memory Technologies

Types of memories:

Volatile

  • Static RAM (SRAM): Volatile memory that uses a six-transistor (6T) cell design to latch data; it is extremely fast, byte-addressable, does not require refreshing, and is primarily used for CPU L1/L2/L3 caches.

  • Dynamic RAM (DRAM): Volatile main memory that stores data in capacitors which naturally leak charge; it requires continuous electrical refreshing, operates with high density at a lower cost than SRAM, and requires complex timing initialization at boot.

Non volatile

  • NOR Flash: Non-volatile memory utilizing parallel floating-gate transistor architecture; it is byte-addressable for reads, supports Execute In Place (XIP) directly from the memory bus, offers high read speeds, and is typically used for system BIOS and bootloaders.

  • NAND Flash: Non-volatile memory utilizing series floating-gate or charge-trap architectures; it is strictly block-addressable (reads/writes in pages, erases in blocks), lacks XIP capability, offers massive density at low cost, and forms the basis of modern SSDs, M.2 drives, and SD cards.

  • Mask ROM: Non-volatile memory with data physically and permanently etched into the silicon during semiconductor fabrication; it cannot be modified under any circumstances and is used for low-level SoC factory Boot ROMs.

  • EEPROM: Non-volatile, electrically erasable programmable read-only memory that allows data to be erased and rewritten byte by byte; it is slow and has low density, making it suitable for storing small configuration metrics or device serial numbers.

  • Phase-Change Memory (PCM / PRAM): Emerging non-volatile memory that stores data by altering the physical state of chalcogenide glass between crystalline (conductive) and amorphous (resistive) phases; it bridges the gap between DRAM and NAND by offering near-DRAM read speeds and byte-addressability.

  • Magnetoresistive RAM (MRAM): Emerging non-volatile memory that stores data using magnetic storage elements (magnetic tunnel junctions) rather than electric charge; it delivers high endurance, low power consumption, and near-SRAM operational speeds.