Here are some common storage technologies used in various storage units:

• RAM: CMOS Transistors, typically using DRAM (Dynamic RAM) or SRAM (Static RAM) technology.
• ROM: EPROM (Erasable Programmable ROM) or Flash Memory (e.g., NAND Flash).
• HDD: Magnetic Disks (using magnetic material to store data).
• SSD: NAND Flash Memory (a type of non-volatile memory).
• Optical Discs (CD/DVD): Laser-etched grooves on a Polycarbonate disc.
• USB Flash Drive: NAND Flash Memory (similar to SSD).
• Blu-ray: Blu-ray Discs use Laser technology to read data from a Polycarbonate disc with a blue-violet laser.
• Tape Drives: Magnetic Tape for data storage.

Reading

• RAM (CMOS Transistors): Data is read electrically by accessing specific memory cells in the array using address lines. In DRAM, a capacitor holds data, and in SRAM, a flip-flop holds data.
• ROM (EPROM/Flash Memory): Data is read electrically by using transistors that control the flow of current based on the data stored. In EPROM, data is read by applying a voltage to the transistor gates; in Flash Memory, cells are read by measuring the charge in a floating gate.
• HDD (Magnetic Disk): Data is read by a read/write head that floats above the spinning magnetic disk. The head detects changes in magnetic fields on the disk surface as it passes over the data tracks.
• SSD (NAND Flash Memory): Data is read by sending electrical signals through NAND cells. Each cell holds data in the form of electrical charge, and the data is retrieved by detecting the voltage levels in these cells.
• Optical Discs (CD/DVD): Data is read by a laser that shines onto the disc surface. The reflected light is detected by a sensor, interpreting the data encoded in pits and lands on the disc surface.
• USB Flash Drive (NAND Flash Memory): Similar to SSDs, data is read by sending electrical signals to the NAND flash cells and retrieving the stored data based on charge levels.
• Blu-ray: Data is read by a blue-violet laser which is finer than the red laser used for CDs/DVDs, allowing for more data to be stored. The laser reads the disc’s microscopic pits and lands, with light reflection interpreted by a sensor.
• Tape Drives (Magnetic Tape): Data is read by passing the magnetic tape over a read/write head that senses the magnetic fields on the tape's surface and converts them into electrical signals.