To .zip or not to .zip, that is the question?

Both FCP application package and the libraries are complex objects. They may contain thousands of files. In general, it's a good idea to zip them before moving, copying, or archiving them. This has two advantages:

(1) Any file or network I/O will be faster due to moving a single large file vs possibly thousands of little files.

(2) The zip file created by Finder's compress function contains a CRC32 checksum which verifies the files were undamaged, if it unzips without error.

However: There is a limitation in the Finder uncompress function so it does not actually verify the CRC checksum. To my knowledge this is undocumented and it's a significant issue.

You can use the MacOS terminal command "unzip" which does do the CRC check. However it does not abort the process but just prints an error to the screen. It is easy to miss.

There is a third-party utility on the App Store called "The Unarchiver". It has Finder integration so you just right-click on the zip file, then select "The Unarchiver". It will do the CRC check and abort if anything in the zip file is damaged. That way you can't overlook it.

There is no problem per se from zipping or unzipping the .app or library package. It's generally a good idea. That alone won't harm the contents.

But if a single bit in the .zip file is altered by transmission errors or bit rot, unzipping can turn this minor error into major damage. This is due to an exponential chain reaction called bit error amplification. You won't notice this with Finder's built-in decompression -- until something bad happens like FCP crashing trying to open the library.

Whether the error is found or not, the file is nonetheless damaged, just in the Finder decompression case you don't know (until something bad happens), and if decompressed by The Unarchiver, you immediately know.

Years ago I tested various zip and unzip utilities and used hex editors to inject small binary errors in the zip file to verify the unzip CRC check always caught it. They seemed to.

Fast forward to last week when I repeated that test using Finder compress/decompress, and I was shocked to find Finder did not validate the checksum on decompression. If you use The Unarchiver to decompress the Finder-compressed file, it will always find the error (if present).

Storage systems are pretty good so you may never see this. Or maybe some have seen this but attributed it to a mysterious FCP bug. The benefit of validating the checksum is it tells you the zip file was damaged between the time it was compressed and the time it was decompressed.

If you are storing these in a separate drive, I don't think there is a problem with keeping the application as such.

But it is important to note that if it is kept in the Applications folder then it can be overwritten, even if it is renamed, so be careful - for example, say you have version 10.7.1 and rename it so it becomes "Final Cut Pro 10.7.1.app" and then do an update to 10.8, it will still overwrite it, despite it not being called "Final Cut Pro.app". I have been burned by this before, and thus I got in the habit of zipping...

I always zip my FCP, Motion, and Compressor applications before upgrading, and just leave the zip files in the Applications folder. Never had issues. I've done test from time to time unzipping and trying them out, no problems. Totally safe. Larry Jordan and Richard Taylor also recommend this.