storage

• main memory (or (primary) memory or RAM (random access memory))

  • volatile
  • DRAM, SRAM

• secondary storage (or secondary memory or storage)

  • nonvolatile

• Non-volatile memory (NVM) (or non-volatile storage)

  • (retains data even when power is off)

• Volatile memory

  • (loses data when power is off)

• disk storage (e.g. optical disc, magnetic disk)

• Magnetic storage (or magnetic recording)

  • magnetic tape
  • magnetic disk
    • Hard disk drive (HDD)
    • floppy disk drive (FDD)

• optical storage

  • optical disc
    • compact disc (CD)
    • digital versatile disc (DVD)
    • Blu-ray disc

• Solid-state storage (SSS)

  • types:
    • DRAM (dynamic random access memory)
    • flash memory
      • nonvolatile semiconductor memory
      • architectures:
        • NOR
        • NAND
      • solid-state drive (SSD)
      • USB flash drive
      • memory card
        • SD card
        • microSD card

• SRAM (static random access memory)

• NVM Express (NVMe)

Hard disk drive (HDD)

• track

• geometrical sector

• disk sector

• cluster

• cylinder

• disk read-and-write head

• $\text{Capacity}=\text{Cylinders}\times \text{Heads}\times \text{Sectors per Track}\times \text{Bytes per Sector}$

• $\text{Platters}=2\times \text{Surfaces}$

• $\text{Tracks per Cylinder}=\text{Heads}$

• $\text{Tracks per Surface}=\text{Cylinders}$

• constant angular velocity (CAV)

• zone bit recording (or multiple zone recording)

• $T=S+\frac{1}{2}R+R\frac{b}{N}$

  • $b=$ bytes to be transferred
  • $N=$ bytes per track
  • $S=$ seek time (time to move the read-and-write head to the correct track)
  • $R=$ rotation time (time for one full rotation of the disk, on average half a rotation is needed to reach the desired sector)
    • rotational latency (or rotational delay or latency)
    • average rotational latency = $\frac{1}{2}R$

• positioning time (or random-access time) $=\text{Seek time}+\text{Rotational latency}$

• rotations per minute (RPM)

• head crash

• bad sector

• trace cache

• Logical block addressing (LBA)