GS checkerboard screen at Bootup = ?

[shall@ccs.carleton.ca (Simon Hall)]

What does the checkerboard box mean when you turn on the gs ?
I am trying to find what I think is a fault in a Memory  Chip.
The option/open apple keys give me a good system.
But, I am having trouble with (what seams to be random W/R errors)
e.g boot system 5.0.4. (maybe it's the system-disk for appleworks GS) 
      format a disk,
      drag and drop system 5.0.4 disk onto the /ram5 icon.
      drag and drop the /ram5 icon onto the new formatted disk.

do a system shut down,
turn the gs off,
turn the gs on with the new copy of the system,
works fine. 
do a system shut down,
turn the gs off,
turn the gs on with the new copy of the system,
START GETTING ERROR #27'S FOR START.GS.OS THEN FST EVEN GOT A -
[DETECTED TRASHED MEMORY -- SOFTWARE BUG OR (LESS LIKELY) BAD RAM
ERROR $0308]

Hanked all the cards from the slot's,
Disconnect the FDHD drive,
Still got the checkerboard screen,
do a option/open apple,
system good!,
connect a DiskII + conntroller card,
boot a prodos8 system disk, all is ok.

put the appleramcard back in the gs,
Connect the FDHD drive
still got the checkerboard screen,
boot the new copy of the system (gs/os),
ERROR #27 GS.OS OR SOME OTHER FILE NAME  ERROR,

MY SYSTEM IS;
GS Rom 1
1280 ram
FDHD DRIVE (NO-CONTROLLER-CARD) It's just plugged in the DiskPort.

I can not seem to find out what that checker board screen means,
I seem to remember that a checkerboard screen on a (gasp--mac) 
means there's bad ram or some other impending disaster approtching.?

regards

jim aka simon
be946@freenet.carleton.ca
shall@superior.carleton.ca
nexus-6@softwords.bc.ca