Question: what kind of ram can i update my ibm r40 model 2681-hu1with? 

Answer: 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
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