Akai S1000 / S1100 samplers

Hi -

Just got an S1000, under "Edit Sample" it says Free = 4,193,024 - 
does this mean there is 4MB of RAM installed and available?

(Only loaded the OS 4.40 disk, nothing else)

I know there are four slots available for RAM, but when I open the 
machine up, I see *five* slots in the upper right. Four of which on
mine are filled (starting with the right-most slot) - what's the 
fifth slot?

(It also has the SCSI and Digital Out cards, so I know it's not one 
of those...)

Thanks,
-a/.