I think I would try testing the RAM. At that time (and I suspect even today) the "-2" variants are speed selected from the general pool, and so the -3 may work reliably at 200ms .... Dave -----Original Message----- From: cctalk-bounces at classiccmp.org [mailto:cctalk-bounces at classiccmp.org] On Behalf Of James Attfield Sent: 03 August 2014 11:31 To: cctech at classiccmp.org Subject: Re: DRAM memory for NorthStar Horizon Ian, I'm afraid my NatSemi data book only goes up to MM5290 (16Kx1 Dynamic) but the '-3' variant is 200nS as is the MM5298-3 and it lists the '-4' variant as 300nS. Unless I had no option I wouldn't use the slower chips whereas the 150nS would do fine although without any real feel for the tolerances of the chips, board design wait circuitry (if exists) or the refresh controllers it is not really possible to say with any degree of certainty.