> But what if I load up a new image?  Is there a default change set that
> will get automatically loaded?
>
> --  
>  Lloyd Zusman
>  ljz at asfast.com

Mmm lets step back to some basics.

a) You've a VM. That's a C program that came from a subset of smalltalk  
called SLANG that is the Interpreter class (and others) in the image.  
The VM excluding some platform unique primitives and the OS support  
structure is written in Smalltalk, then translated to C. You'll also  
notice classes ending in Plugin, those too are translated to C, and  
either are fully self contained, or call out to platform specific C  
implementation code.

You can run an image file within the image using the Smalltalk  
Interpreter by doing

  interp _ InterpreterSimulator new openOn: 'mini.image'.  where  
mini.image is the image you want to open.
Well you should be able to, we have a bad habit of breaking it. I think  
it's broken again.

b)  You've the image file (I've 98 of them on my hard disk right now,  
even after cleaning things up a bit. Wouldn't want to count the VM I've  
got about).  That contains the bits born upwards of long ago.  Some  
Smalltalks like Smallscript acually use a declarative form of Smalltalk  
to "create" all the bits at startup time, versus using old bits. Cool,  
but the important piece is that on a save the bits are archived (a  
snapshot) to disk and you quit, on restarting the bits get read in and  
you continue where you came from, with shutdown and startup code  
(hopefully running correctly).

c)  The change file (optional I might add since you can have an image  
without a change file) is the archived log of *all* the changes you  
have made to the original source code, that is there for recovery,  
review, undo, audit, etc. You can consolidate changes into change sets  
which then you can apply to other images. In really large smalltalk  
systems you might have a 'librarian' who's role is to mange those  
change sets (using Envy or Store or some other versioning system).

d) The SqueakV3.source is a file that contains all the source code in  
the image that was consolidated from a previous source file and change  
file in the past (actually when 3.0 was born). That is static, I've  
only one on my machine and 98 aliases that point to it.

e) Not having access to the source or the change file isn't a problem  
to run the image, it's a problem if you want to edit because you lose  
comments, variable names etc. However you still can edit because the VM  
falls back to decompiling the bytecodes and presenting the source code  
that would create the bytecodes. Ah but if you mismatch the changes  
file to an image file you run into more serious problems because  
indexing into the changes file to grab the text to display gets really  
confused.

f) On starting the Squeak VM, it looks for a image/change file set to  
use, say squeak.image & squeak.changes.  Otherwise you could drag and  
drop or give command line to indicate a different change set.  say  
Zusman98.image, by agreement the change set needs to be called  
Zusman98.changes. Thus you get 98 images/change sets on your hard disk.

g) Most VMs only will allow you to start one image, unlike some  
programs that would let you open multiple documents. I'm not sure  
offering this would be useful? Since you can just start another VM  
application and point to a different image/change set. MMm I think the  
mac Cocoa version allows this.

h) various plugins exist, FFI, mpeg, matrix? (mystery plugin as far as  
I know). Those live either in a plugin folder, or loose in the  
directory of the VM. They are shared libraries/bundles/DLLs and help  
reduce the memory footprint by excluding their overhead for small  
platforms that wouldn't support MPEG for example.

PS I'm sure I've missed something.

Only memory will prevent you from running say 98 image/change sets and  
98 VMs at the same time.

--
======================================================================== 
===
John M. McIntosh <johnmci at smalltalkconsulting.com> 1-800-477-2659
Corporate Smalltalk Consulting Ltd.  http://www.smalltalkconsulting.com
======================================================================== 
===