Comparing the acad*.lsp files

Beginning with the AutoCAD 2000 release, AutoCAD uses different startup files for the automatic loading of AutoLISP, when compared to previous versions of AutoCAD. This solution discusses the user-defined startup files acad.lsp and acaddoc.lsp, and the reserved startup files acad2000.lsp and acad2000doc.lsp (later releases will include the year corresponding to that release, e.g., acad2011.lsp and acad2011doc.lsp).

acad.lsp
When you start AutoCAD, it searches the library path for a file called acad.lsp. If the file is found, AutoCAD loads it. AutoCAD loads acad.lsp once only, at the beginning of the drawing session.

Functions and variables defined in acad.lsp are only available in the first drawing in an AutoCAD session. If you want a routine to be available in all drawings in the session, include it in the user-defined startup file acaddoc.lsp.

Note: AutoCAD 2000 is not supplied with the user-defined startup file acad.lsp; you create and maintain the file yourself.

acaddoc.lsp
Every time a drawing opens (that is, when you start a new drawing or open an existing drawing), AutoCAD searches the library path for a file called acaddoc.lsp. If the file is found, AutoCAD loads it.

Note: AutoCAD always loads acaddoc.lsp regardless of the settings for the ACADLSPASDOC and LISPINIT system variables.

Functions and variables defined in acaddoc.lsp are available in all drawings in the AutoCAD session.

In most situations, you only need one acaddoc.lsp file, but you can use different versions of the file. For example, because AutoCAD searches the library path for acaddoc.lsp, you could place a different acaddoc.lsp in each drawing directory. Then AutoCAD would load specific AutoLISP routines for certain types of drawings or jobs.

Note:  AutoCAD 2000 is not supplied with the user-defined startup file acaddoc.lsp; you create and maintain the file yourself.

ACADLSPASDOC system variable
You can use ACADLSPASDOC to override the recommended functionality of acad.lsp. If ACADLSPASDOC is set to 0 (the default setting), acad.lsp is loaded once, at the beginning of the drawing session. If ACADLSPASDOC is set to 1, acad.lsp is reloaded every time a drawing opens.

ACADLSPASDOC and SDI mode
ACADLSPASDOC is ignored in SDI (single document interface) mode. When the SDI system variable is set to 1, LISPINIT controls the reinitialization of AutoLISP between drawings. When LISPINIT is set to 1, AutoLISP functions and variables are valid in the current drawing only; each time you start a new drawing or open an existing one, all functions and variables are cleared from memory and acad.lsp is reloaded. Changing the value of LISPINIT when SDI is set to 0 has no effect.

acad2000.lsp
Do not modify the reserved file acad2000.lsp; it contains AutoLISP-defined functions required by AutoCAD. The file acad2000.lsp is loaded into memory immediately before acad.lsp.

acad2000doc.lsp
Do not modify the reserved file acad2000doc.lsp; it contains AutoLISP-defined functions required by AutoCAD. The file acad2000doc.lsp is loaded into memory immediately before acaddoc.lsp.