Topic:
What are RAM volumes used for?

Description:
        

Solution:
A RAM (Random Access Memory) volume consists of seismic data, that normally
resides on disk. It can be loaded into memory for rapid access by ASAP. Using
RAM volume speeds up the picking process.  The RAM volume can also be saved to
file for use in subsequent IESX sessions.  A RAM volume is usually a subset of
the whole survey, typically limited in the X, Y, and Z direction. 

The data is loaded into memory in fractional 8-bit format, regardless of the
format of the data stored on disk. A scaler is applied to the whole volume, as
opposed to a trace-by-trace scaler used by the data on disk. This scaling may
result in some clipping of very high and low amplitudes, which can result in
incorrect picking over these clipped zones. If this starts happening, look at
the data in Seis2DV/3DV on a large scale to check for high amplitudes an
clipping. You can also run ASAP over this range using the data on disk, then
compare this picking against the picking from the RAM volume.

The disk file is saved on the last DSL in the seismic list. If there is
insufficient space on this disk, the DSL's are searched in reverse order for
space to load the file. These files do not appear in the IESX > DataManager >
Move files list. If there are not seismic DSL's, the default DSL's are used in
the same way.

If there is a significant difference between the picks from the RAM data and the
disk data, you have several options:
	Use a RAM volume but pick in the Instantaneous Phase mode.  The data is
	converted to reflection strength and is less susceptible to clipping
	problems.

	Use the data on disk rather than RAM.  To save run time try to limit the
	data to be picked by this method as much as possible.  Also, use the 
	Vertical Limits option; this will reduce run time.

	Using Computation Manager, run a short AGC on the data prior to picking
	to reduce the extreme amplitudes of the data.  After the AGC, you may,
	if you wish, load the data to RAM.  Remember that such data is for
	picking purposes only and may be deleted as soon as it is convenient.



Last Modified on: 14-DEC-98