What is computer memory?

Hi neo,

Hard disks are using magnetism to save data. CDs and DVDs use optics to save data. Flip-flops and transistors use electricity to save data.

Hard disks and CDs are divided up into small parts (bits) on the surface. Each small part is either 1 or 0. In a CD that’s 0=reflecting and 1=not reflecting. In a hard disk thats 1=magnetic and 0=not magnetic.

Magnetism of hard disc sectors can be changed easily by the read-write-head of the disk it changes the bits from mag to nonmag and vice versa. It needs electricity to read or write data, but the data remains on if you unplug the HD. Transistors or flip-flops are very much faster, but they need a constant source of power or they lose all data. That is the case with RAM. The short-term memory of the computer. If you have a sudden blackout, all Data in your RAM (as in: the changes in your Word document ever since last time you clicked the ‘save’ button) is lost.

Optics in a CD is mostly write-once and read-only afterwards. Then you got a completely reflecting disk and you burn holes into the reflecting layer with a LASER. Re-write is difficult but possible. Rewritable CDs have a reflective layer that can be molten by a weaker LASER in the cd drive and thus return the bits to the condition where they reflect light. Needs special drives and special blank-CDs.

You can kill the Data on your hard disk by putting it in the microwave for 3 seconds, by applying a large and strong magnet( the sort that you find inside larde loudspeakers) or by carrying it into a hospital where they have a magnetic resonance tomography tube.

hope this helps If you want more details, use wikpedia. There are thousands of techs who seem to have nothing to do except discussing the exact binary coding sequels of a blue-ray disc on the wikis.

bye the sheep