Fujitsu fi-5900C Operator's Manual page 248

The memory listed below is recommended. Two modules of the same specification must be installed at the
same time.
The memory modules are not provided with the scanner.
Manufacturer
Micron Technology
ATTENTION
HINT
228
9.4 Other Options
Memory type: 144-pin Unbuffered DODIMM
Model
MT8LSDT3264HY-133D2
The scanner may not function properly if two modules of different types
are installed at the same time.
You can confirm whether the memory modules are installed properly or not
through the [Software Operation Panel]:
Click the [Device Setting] tab and check the value of scanner memory under
"Standard Information".
Size
256MB