Question about UMBs

        Hi all,
  I learned this several years ago, but I've never done anything with it 
since, so... I'm wondering how a UMB provider informs DOS that there's 
now memory about the video buffer at A0000-BFFFF? I know it has 
something to do with the MCB chain, but I can't remember any specifics.

  Also, a somewhat related question (related because it deals with 
memory usage), is it possible to create a .sys file, loadable by the 
DEVICE command in config.sys, that won't take any memory after 
initialization? Meaning, it loads, does its job, and is completely out 
of memory afterwards.

    Thanks in advance,
        Paul Case