System Configuration Utility

We are running 1Ghz computers with Win 98 SE and 256mb of memory. In an attempt to resolve a problem we were having with McAfee Virusscan software, we changed the “Limit memory to:” setting in the Win 98 ‘System Config Utility’, ‘Advanced’option from 256mb to 128mb. This solved the problem immediately and didn’t seem to affect the performance of the computer at all. I am concerned however that we may have eliminated the other 128mb of memory from being accessible. Is this true ? What are the negative affects of making this change ? Does it only restrict the operating system to 128mb and leave the remaining memory free for other programs to use ?