Learn Arabic (Modern Standard): معمارية البروتوكول بمثابة جسر بين الشبكة والخادم. - The architecture of the protocol serves as a bridge between the network and the server.

The phrase بمثابة (bi-mathābati) forces the noun immediately following it into the genitive case. Therefore, جسر (bridge) takes the genitive form, pronounced as جسرٍ (jisrin). The phrase essentially acts as a preposition meaning 'in the position of' or 'tantamount to'.

Where is the verb in this sentence for 'serves as'?

There is no verb here! This is a nominal sentence in the present tense. The subject is the architecture, and the predicate is the prepositional phrase بمثابة جسر. Arabic doesn't use a copula verb like 'is' here, and the concept of 'serves as' is entirely covered by the phrase بمثابة.

Why doesn't معمارية take the definite article الـ if it translates to 'The architecture'?

معمارية is the first term in an Idafa (genitive construction) paired with البروتوكول. In an Idafa, the first word never takes the definite article, but it automatically becomes definite because the second word is definite.

Is الخادم the standard word used for a computer server in Arabic?

Yes, it is. You likely learned خادم as 'servant' or 'attendant' in earlier levels. In modern IT and networking contexts, it is the standard, literal translation for a computer 'server'.