Various Apple products, even though they leave the factory at the same
time, may contain different versions of system software. Here are some
reasons why:
- The product may be shipped with the version of system software under
which the product was tested. With many Apple products, there is a long
test cycle, and it is difficult to re-test the product and change the
system software version just before the product's release.
- When new system software is released, it takes time, due to build
schedules, for the new software version to be incorporated into the
product's packaging.
- Sometimes, a specific modification to the system software is required
for a new product. For example, the LaserWriter IISC, which required
modifications to the System file and was shipped with System 4.3, which
was not a general release.