There are two gerber standards, 274D and 274X. 274X has the aperture information embedded in the gerber file, 274D has a seperate aperture file. I have a program I wrote to merge 274D files and aperture files into a 274X file, as many board houses no longer accept 274D files. The PCB package I use only generates 274D files. http://www.lh1.org/autotrax/autotrax.html I use Protel Autotrax. This is a formerly commercial program, which is now public domain. It is a DOS application. It supports up to eight layer PCBs, with no limit on the number of components or board size (up to 32 inches by 32 inches). It has an autorouter, which I never use. I have created PCBs up to 12 inches by 12 inches with over 1200 components using this package. Although the 274 spec allows multiple layers to be placed in one file, I don't know of any board houses which support that format. I use a standard file naming convention, but board houses usualy like to get a text file listing which file is which layer. Advanced circuits has you assign layers to files when you upload your data. Here is a typical readme file: GERBER TOP LAYER FILE NAME ;FLUXGATE.GTL GERBER BOTTOM LAYER FILE NAME ;FLUXGATE.GBL GERBER TOP SOLDER MASK FILE NAME ;FLUXGATE.GTS GERBER BOTTOM SOLDER MASK FILE NAME ;FLUXGATE.GBS GERBER TOP COMPONENT MASK FILE NAME ;FLUXGATE.GOV GERBER BOTTOM COMP MASK FILE NAME ;FLUXGATE.GBO ASCII NC DRILL FILE NAME ;FLUXGATE.TXT NC DRILL TOOL SIZE FILE NAME ;FLUXGATE.TOL A friend of mine maintains a open source pcb layout program, available at: http://opencircuitdesign.com/pcb/