text: your ibm thinkpad r40 model 2681 need DDR PC2700 • CL=2.5 • UNBUFFERED • NON-ECC • DDR333, maximum is 2 modules of 512MB.\nhttp://www.crucial.com/store/listparts.asp?Mfr%2BProductline=IBM%2BThinkPad&mfr=IBM&tabid=AM&model=ThinkPad+R40+Series+%28Type+2681%29&submit=Go