Which is correct when referencing an operating system version "OS X 10.6.x and later" or "OS X 10.6.x and above"?
Bonus points for providing the why.
At the computer magazines where I work, our house style is to use "OS X 10.6.1 or later" when referring to a situation where the content of the sentence suggests that we're talking about an individual machine (hypothetical or not) that will be running one particular operating system:
Similarly, we use "OS X 10.6.1 and later" when we're talking about multiple versions of the OS:
We try not to use "or above," "and above," "or up," or "and up," mainly because we view version numbers as being essentially timeline markers rather than markers of quantity. The expressions "or newer" and "and newer" would be fine under this interpretation of version numbers, but we've tried to standardize on one expression for greater consistency in presenting the information to readers.
I wouldn't claim that any of the expressions I've mentioned here are fundamentally incorrect.
Pragmatically speaking, above and later are not synonymous in the given context, although above has necessarily to be later.
Think of it this way. Version numbers are always assigned in increasing order with passing of time, i.e., a version released later has a higher version number. Fine.
However, a version released at a later date may have the same version number as its predecessor or none if the product had no version numbers so far. In this case, versions are referenced by date, not by unique numbers: Release may be a more appropriate qualifier in this case than version.
Whatever the case may be, language wise, a version above is strictly one with a higher version number, while a later version is naturally one released at a later date. It is obvious therefore, that they are not synonymous.
Even in a situation where you are referring to, or mean, a version that's both higher and later, it is important to focus on which aspect is relevant or significant to the context.
Of the entire discussion above, only the linguistic aspect is relevant here on ELU. For a more technical answer, you should raise the question on the appropriate tech site such as SO [stackoverflow.com].
"Later" is more appropriate. "Above" is more ambiguous, and could be misleading if a download web page, for example, lists the earliest versions first. Use "later" when talking about time, and "above" when talking about location.