Data Storage

//RAM vs ROM — the table you must know

This comparison appears almost every year.

           RAM                     ROM
volatile?  yes                     no
read/write both                    read only
holds      programs & data in use  start-up instructions
size       large                   small
changes?   contents change often   fixed

//The three storage technologies

Magnetic (hard disk): a spinning platter magnetised in one of two directions; large and cheap, but has moving parts so it can be damaged by knocks. Optical (CD/DVD/Blu-ray): a laser burns pits and lands into the surface and reads the reflection; cheap and portable, but small capacity and scratches easily. Solid state (SSD, USB stick): no moving parts, uses transistors that trap charge; fast, silent and robust, but more expensive per GB and has a limited number of write cycles.

//Virtual memory

When RAM is full, the least-used pages are moved out to the hard disk, freeing RAM for what is needed now. It lets you run more programs than would otherwise fit — but the disk is far slower than RAM, so heavy use causes 'disk thrashing' and the computer slows down.

//Cloud storage

Files are stored on remote servers run by a company. Benefits: access from anywhere, no need to buy hardware, automatic backup, easy sharing. Drawbacks: needs an internet connection, ongoing cost, and you are trusting someone else with your data's security.

KEY TERMS

CHECK YOURSELF