Okay a few things....
INtel 4 procesor (3.20 ghz) 512 ram
File 1 (single line dwg) 220 kb
file 2 - xref topo 4,547kb
file 3 - xref boundary 300 kb
file 4 - xref title block 169 kb
If I open the Topo (file 2) I can REA regen all in less than 2 seconds. If I open File 1 that calls all...