Mass storage devices (magnetic disks, optical disks, and magnetic tape) have slow access times and low transfer rates. They are also located far from the processor. These mass storage devices are not even on the motherboard. (Sometimes they are not even in the same box as the motherboard!) But, mass storage technologies also have several important advantages:
- They are nonvolatile —meaning that information is not lost when power is turned off.
- They have huge capacities, measured in billions or even trillions of bytes.
- Their cost per bit stored is far lower than RAM.
- In some cases, they use removable media that can be popped into a drive, used as needed, and then taken out of the drive, or mailed to a friend. Several newer removable disk technologies have appeared since the 3.5-inch floppy (1.44 MB). The Iomega Zip drive uses removable disks with capacities of 100 to 750 MB, and the CD Read/Write drive uses writable optical disks with 650 MB or 700 MB of storage capacity. These days, the compact flash drives (also called thumb drives) which plug into USB ports have taken over the duties of the floppy or Zip drives. The memory capacity of these flash drives range from 128 MB to 16 GB. On the higher end, we now have external hard drives with 1 TB storage capacity. These types of drives are currently popular for making backups of a system's main hard drive, or for transferring large data files from one site to another. On the optical side, we now have dual layer writable DVD disks which have a storage capacity as high as 17GB. As hard drive capacity increases and optical disk technology matures, creating backups on external hard drives and re-writable optical disks has become a popular alternative.
