Try this command in your config.sys for DOS 7 (win95) device=himem.sys /A20Control:ON See the web page http://log.on.ca/users/rhwatson/dos7/v-himem-sys.html for tips on getting himem to work for specific PC's. Tom Turak Rick, I don't have a 486 manual in front of me, so I can't give you exact details. There is a setting in CMOS which controls the A20 line. Find that setting and compare it with one of the boards that is working correctly. Jim Meagher -----Original Message----- From: Rick van Heyst <[log in to unmask]> >Greetings, >The problem is as follows: When we boot up DOS 6.22 and the Himem.sys >driver is loaded in Config.sys we get the message: "ERROR: Unable to >control A20 line XMS driver not loaded". > The PCBUILD web site always needs good submissions. If you would like to contribute to the website, send any hardware tech tips or hardware reviews to: [log in to unmask]