What is a good word for a lack of knowledge on a particular subject matter?

I would like to know if there is a word for the above situation. Particularly, I would like a word that replaces "X" in the following sentence:

You are so computer-X.

If it has to, it could fit in the following sentence:

You are so X when it comes to computers.

I have words for both, but the first is not a very intellectual one. The word I have for the first sentence is "ignorant". I don't like that word in this context, though, because it is fairly common. I would like an uncommon word for the former sentence. For the latter sentence, I have the word "inerudite", if I am using it properly in that sentence (it would be nice to know if I am not). I can live with using the using the second word and the second sentence, but I would like to know, is there a better word than "ignorant" that will satisfy the grammatical conditions of the first sentence?

You could go with "illiterate".

illiterate

displaying a marked lack of knowledge in a particular field

Source: Dictionary.com

Someone posted the answer for which I was looking. I know not of why, but the individual's answer was removed, so for those that happen upon this, the word that was presented in the post was nescient.

Nescient:

: lack of knowledge or awareness

lack of knowledge; ignorance.

The correct English word is ignorant, which means to have a lack of knowledge about something. Unfortunately many people believe the word means 'stupid' (it doesn't) and so take offence if described that way. If you don't think the person described will have a problem with it, that's the word to use.

I don't feel “ignorant” works in this context, because that would imply "not being aware" of something rather than "not being familiar with", which is what I think is meant.
I agree on "Computer illiterate" being an option. Below is another two words you could consider. In my home language, Afrikaans we have a great word to describe this situation, namely the word "leek”, for which the English translation is:
1. “Layman” Personally, I don't find it all that easy on my ear, but by definition (below) it is suitable in this instance. Google Definition: “ a person without professional or specialized knowledge in a particular subject” Google Example: "the book seems well suited to the interested layman" a. “Novice” Similar to the word, amateur, a word used to express something being “new to” a person.

I suppose another perspective on the words mentioned above that may help clarify their meanings as well as the difference between them, would be to rank/sort them according to “level of familiarity”: Ignorant: Level 0 – meaning “not even aware of…” Layman: Level 1 – meaning “no knowledge of…” Novice: Level2 – meaning “very little knowledge of…”