I need to know the meaning and tense of these sentences:
(A) "This feature is added to the last version."
(B) "This feature was added to the last version."
I can't understand the difference between "is added" and "was added". Is there any difference between these two sentences, or do they mean the same thing?
This feature is added to the last version.
is not grammatical. It is not now being added, since the last version is already out there.
This feature is added to the current version.
This feature is added to this release.
These sentences still do sound a bit off though, you would normally find them as:
This feature has been added to the current version.
This feature has been / is being added to this release.
("is being" if the current release is still in development.)
For others than the current version:
This feature was added in the last version.
This feature will be added in the next version.
"Is added" is used to describe a change in functionality based on some action or event:
This feature is added when you upgrade to the newest version.
This feature is added by selecting the option in the "options" screen.
There is a very subtle effect at work in your examples which causes them to represent not two different sentences but four. The effect may be called deverbalization.
As you know, participles are called that because they “participate in” two different parts of speech at the same time: they may act as either verbs or adjectives—or both.
Which of these functions is/are in play varies from one utterance to another. Sometimes the verbal function is dominant:
This feature was added by the developers in release 3.2.2. ... Here the phrase by the developers names an Agent, so we must interpret added as an action, not an adjective.
Sometimes both are present at once:
This feature, added to satisfy a specific client in release 3.2.2, has been removed. ... Here the ‘adverbial of purpose’ to satisfy &c demands that added be interpreted as a verb—only actions can have purpose—but the word acts as an adjective modifying feature.†
And sometimes the verb function disappears entirely:
This was an added feature in release 3.2.2. ... Here added acts as an ordinary adjective, equivalent to “new”. Participles used this way are called deverbal adjectives or deverbals.
Where this gets tricky is when the participle is used with the verb BE, as in your sentences: This feature is added. Does the participle here act as a component of a passive construction, equivalent to “Somebody added this feature”, or is it a predicate adjective, equivalent to “This feature is new”? Only context can tell you.
In your sentence in the past tense it probably doesn't matter. The sense is pretty much the same whichever reading you give it: at some time in the past a new function was added. But in the present tense we have two options, simple present and present perfect. As oerkelens tells you, we ordinarily employ the present perfect when the passive verbal sense is intended:
This feature has been added to the latest version.
The present perfect tells us that the action occurred in the past but has a current result. And we tend to read a simple present is added as a predicate adjective = “is new”. The reason why folks are uncomfortable with is added in the last version is because the present-tense attribution of “newness” doesn’t fit well with last version, something from the past. If you mean to say that the feature is a new one—perhaps you are reviewing the software—you will do better to speak about the version as one which is current:
This feature is added in the latest version.
†Many contemporary grammarians ‘resolve’ this ambiguity by understanding added to satisfy &c as a ‘reduced relative clause’—that is, as the relative clause which was added to satisfy with the which was deleted. My own opinion is that this is wrongheaded; but it may be helpful to you to think of it that way.*
Is added : current , or upon a certain action, like your grade is added to the system when the professor uploads it
Was added : past, as in your grade was added last night
