A ramdisk ( or ramdisc ) filesystem stores data directly to memory
instead of a hard disk drive providing the fastest data I/O available
to increase performance of applications.  All of the standard hp-ux
data access commands are compatible with ramdisc filesystems.

Why is a ramdisc faster than a conventional disk drive?

A ramdisc has no mechanical moving parts and  all data is stored
in main system memory.   A disk drive  stores data on platters that
spin at  a high rpm with  read and write  heads that move across a
set of platters to access the data. The animated image represents
the method that data is retrieved.  Move your  mouse over  the disk
drive  to  start  the  animation.  The  red colored  dots  represent  a
request for data.  The drive heads read the  VTOC ( Volume Table
Of Contents ) then move to a location on the platter where the data
is stored.  Depending on rotation,  the read head may have to wait
for another revolution before it can  read or write any of the data on
the  platters.  The  yellow colored  dots  represent  the  data being
sent back to the  system. If you remove the mechanical limitations
by using a  solid state disk,  your performance will improve but not
to the degree of a ramdisc due to SCSI bus or PCI bus speeds as
compared  to the speed of a memory bus.  The image on the right
is a disk drive with the top cover removed.  Your data  is more than
likely  not stored  sequentially on the  platters  so there  are delays
within a busy disk drive to retrieve or write the data as well.