Storage Hierarchy

Registers 
Very Fast (1ns)
Very Small
(512 Bytes)
Very Expensive (part of CPU)
Cache
Very Fast (10ns)
Small
(2 MB)
Expensive ($50/MB)
RAM
Fast (100ns)
Large
(256 MB)
Inexpensive ($0.58/MB)
Hard Disk
Slow (10ms)
Very Large (40 GB)
Very Inexpensive ($0.0015/MB)
Off-Line Storage (tape backups, etc.)
Very Slow (in seconds)
Potentially Huge (TBs)
Least Expensive