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Updating from Version 3 and Below
By default, Mathematica Version 4 is installed in a separate directory and not over Version 2 or 3. The files used to save default settings are also separate and will not overwrite any previous preferences files. You must use a new password for Version 4.
Packages written with Version 2 or 3
Most packages written in Mathematica Version 2 or 3 run unchanged under Version 4. A very small number of functions have been modified in ways that could cause problems. Please see Appendix A.13 in The Mathematica Book for the list of incompatibilities.
Mathematica 4 supports remote kernel connections to kernels from Version 3.0.1 or later. You may also connect a front end from Version 3.0.1 or later to a Mathematica 4 kernel.
Using the Applications Library with Version 4
Most application packages written for Mathematica Version 2 or 3 should run unchanged under Version 4. Because some Mathematica functions have been modified, packages that use those functions may be affected.
Application packages need to be copied into a specific directory, based on whether you have administrator privileges:
The same command as in Versions 2 or 3 will work to load the package. If Version 2 notebooks are included in the package, you can convert them simply by opening them in Version 4.
Notebooks in Version 4
The format of notebooks in Version 4 is different from 2.2 and earlier versions. A notebook now is a Mathematica expression and is stored in a single platform-independent file with the extension .nb. All the information necessary to open the notebook is stored in the .nb file.
When you open a notebook that was created with Version 2.2 or earlier in Version 4, a dialog box will appear that allows you to convert your notebook automatically. You have the option of converting input and output cells into StandardForm cells, which will automatically typeset characters and formulas.
You can also use the kernel function NotebookConvert to convert notebooks to the newer format. NotebookConvert is useful if you have a large number of notebooks to convert and you don't want to open each notebook individually within the front end.
NotebookConvert[notebook] converts notebook to the new format and saves the result in a file. The name of the new notebook is based on the name of the old notebook, except that the extension .nb is used in place of the .m or .ma extension that was used in previous versions of Mathematica.
Although NotebookConvert is a kernel function, the actual conversion is handled by the front end, so notebook names must be specified in a way that is appropriate for the front end, rather than for the kernel. If the notebooks that you want to convert are not in the same directory as the directory from which you launched the front end, then the notebooks should be specified by giving the directory path relative to the front end directory, or by giving an absolute pathname.
You can use Scan[NotebookConvert, list] to convert all of the notebooks listed in list. If the kernel and the front end are running on the same computer, you can use NotebookConvert[dir] to convert all of the files in the directory dir.