Using Old and New Versions of Max on the Same Machine
As you make the transition to Max 5 from an older version, you may wish to run old and new versions side-by-side or at least keep them both installed at the same time. Here are some hints to make this easier.
Don't Overlap Your Search Paths
By default, when you install Max 5, everything except your preferences will go into a single self-contained folder. Nothing from your previous Max version will interfere with the installation of any previous version of Max.
For best results, you'll want to keep two separate copies of every file specific to each version. The main reason to do this is that Max 4 cannot read patcher files created by Max 5, so if these files begin to appear in the search path, Max 4 may not behave properly. Not only will it be unable to interpret the files as patchers, it does not know how to read Unicode text files, so it can't necessarily read them as text files either. If you write data files containing extended characters with objects such as table or coll, they may be unreadable in older versions. This issue extends to things like scripts for the js and jsui objects. If you use extended characters in these scripts, you cannot easily maintain a single version that works in both Max 4 and 5. The moment you save the file in Max 5, it will be unreadable in Max 4. The Javascript engine used by Max 5 requires the script to be in Unicode. Max 5 can convert legacy Macroman text files to UTF-8, but it will not save in this format.
Mac users might be tempted to use the technique of creating an alias to their Max 4 world and dropping into their Max 5 search path. As explained here, folder aliases do not work in the search path in Max 5 as they did in Max 4. Furthermore, the same version compatibility and search path problems will crop up if you do this.
Instead of trying to manage one set of files, make a copy of all your files and move that into your Max 5 search path.
Preferences Won't Overlap
As explained here, Max 5 does not share preferences with older versions. Preferences files from older versions are not compatible with Max 5. Do not attempt to copy them. Use the Max 5 environment to create new preferences.
Copying and Pasting Text
Max 5 does a better job of interpreting and importing Max 4 patch data than Max 4 does. So, if you want to create something in Max 4, copy it to the clipboard, switch to Max 5, and paste it into a patcher, you should have no problems, assuming that all references in the patcher data can be resolved. You can also copy Max 4 text format patcher data from an e-mail client and paste it into Max 5, using either the Paste command in the Edit menu or the New from Clipboard command in the File menu.
CPU Utilization
With comparable scheduler settings, Max 4 has a slightly higher CPU utilization doing nothing than Max 5 does. So if you are trying to gain a bit more CPU while using Max 5, you may wish to quit Max 4 temporarily.
Virtual MIDI Ports (Mac only)
One confusing issue that arises when trying to run Max 5 at the same time as an older version of Max is that the virtual MIDI ports created by the Mac version called "to Max/MSP 1" and "from Max/MSP 1" appear to be doubled. Due to the fact that old patches may store references to these virtual ports by name, it was not possible to give them new names in Max 5 to distinguish them from the ports in Max 4. Furthermore, you will be confused because one of the ports with the same name will do the opposite of what you expect (it will be output when you expect it to be an input). To help eliminate the confusion, the virtual ports of other applications are shown in italics in the Max 5 MIDI Setup window.