Persistent Storage: Hard Drive, Flash Drive

• Persistent storage
  aka "non volatile" .. preserved when not powered
• File system - files, folders
• Hard drive - stores bytes as a magnetic pattern on a spinning disk
  High pitch spinning sound you may have heard
• Flash drive - stores bytes as electrons in a chip
  Solid state approach, aka "flash memory"
• Flash drive forms - usb key, SD card in camera, flash chips built into a tablet
• Flash used to be very expensive, so most computers used drives
• However flash is getting cheaper (Moore's law)
• Not to be confused with "Adobe Flash", a proprietary media format

Persistent storage - long term storage for bytes as files and folders. Persistent meaning that the bytes are stored, even when power is removed. A laptop might use a spinning hard drive (also known as "hard disk") for persistent storage of files. Or it could use a "flash drive", also known as a Solid State Disk - SSD, to store bytes on flash chips. The hard drive reads and writes magnetic patterns on a spinning metal disk to store bytes, while flash is "solid state" .. no moving parts, just silicon chips to store bytes. In either case, the storage is persistent, in that it maintains its state even when the power is off. A flash drive is faster and uses less power than a hard disk. However, per byte, flash is significantly more expensive than hard drive storage. Flash has been getting cheaper, so it may take over niches at the expense of hard drives. Flash is much slower than RAM, so it is not a good replacement for RAM. Note that Adobe "flash" is an unrelated concept; it is a proprietary media format. Flash storage is what underlies USB thumb drives, SD cards for use in cameras, or the built-in storage in a tablet or phone, such as 16GB