Updated September 16, 2011
RAM - Random Access Memory
HHD - Hard Disk Drive
Smaller amount (typically 2 GB - 16 GB)
Larger amount (250GB to 1 TB or more)
Temporary storage of files and programs.
Permanent storage of files and programs.
A little like your real desktop - has only your current work on it.

Like a file cabinet - has long-term storage of work.

Contents disappear when you turn off power to the computer.

Contents remain when you power  off the computer (they don't disappear unless you purposely delete a file or folder.)

Contents disappear when the computer crashes.

Contents remain when the computer crashes.

Consists of chips (microprocessors.)
Consists of hard disks (platters or SSD.)
A temporary copy of the opened file and all changes, are kept in RAM until the file is saved.

Until your changes are saved, the original file remains on the HDD. Once saved the new changes are written to the disk drive.

It's easy to get RAM (memory) and the Hard Disk Drive (HDD or Hard Drive) storage space confused. The HDD is where all your programs and data are permanently kept.  RAM is a smaller, faster, temporary storage area.  An "out of virtual memory" error does not mean your Hard Drive is getting full, and deleting files will not resolve the problem. The solution is to increase the size of virtual memory, add more RAM or both.
Updated April 3, 2015
Coronado Computer Service