2.2 Storage Devices

2.2 Storage Devices

1. What is a storage device?

   • Secondary storage is non-volatile disk space.
   • Secondary storage is sometimes called auxiliary memory or secondary memory.
   • Secondary storage is used to store files such as photos, documents and program files. It is used to store any other information that is needed long term.

2. Backing storage.

   • All computers will have backing storage, this is a form of internal secondary storage.
   • This is needed to store data and programs when the computer is turned off.
   • The size or capacity of the backing storage represents how much storage space there is.
   • HDD
     • HDD is the older technology which works by spinning a disc round inside the device.
     • Data is stored on invisible magnetic tracks (rings) on the disk using read/write heads which move to the track then copy the data from the track to the RAM (read) or record data from RAM to the track (write).
     • HDDs have RAM memory inside them that is used as cache to make the drive work quicker by reading ahead or behind the current data so that the next data is already available. This technique allows speed matching of the slower device to the quicker device.
     • Write acceleration is also achieved as data can quickly be copied to cache then written to the slower disc.
     • The performance of the HDD can decrease overtime as the data fragments.
     • Seek time: Average time it takes to find the data.
     • Data Transfer Rate (DTR): How quickly the data can travel to/form the HDD.
     • Spindle speed: How quickly the disc spins.
   • SSD
     • SSD is the newer technology of backing storage. SSDs use flash memory and has no moving parts unlike a magnetic drive such as a HDD.
     • An SSD has faster access to data because it has no moving parts so spindle speed or seek time is not slowing down the DTR.
     • SSDs do not suffer from defragmentation because they have no moving parts. They are also shock proof and use less power for the same reason. However SSDs are more expensive than HDDS
   • SATA cables are used to connect the backing storage in a desktop PC whereas in a laptop the backing storage is connected directly to the motherboard.