Documents are piled up on the desk.
I start up the desktop computer.
noun which may take the genitive case particle 'no'
theoretical; academic; armchair; paper-based; not yet implemented
Figurative use: ideas, plans, or discussions that exist only on paper or in theory, not yet tested or realized. Strongly associated with the set phrase 机上の空論 (armchair theory).
See also: 机上の空論
His proposal is nothing more than an armchair theory.
It seems workable as a paper plan, but in reality it's difficult.
I put the documents on the desk.
That plan was only worked out on paper and has never actually been tried.
空論 is a noun meaning an empty, unworkable theory, closely tied to the fixed phrase 机上の空論, while 机上 alone just marks something as desk-bound or theoretical.
卓上 describes something physically sized or designed to sit on a tabletop, like 卓上コンロ, while 机上 is more often used abstractly, as in 机上の空論 (an armchair theory).
机上 stresses that something exists only in theory or on paper (as in 机上の空論, 'armchair theorizing'), while 紙上 simply means something appears in written or printed form without that negative nuance.
Standard kanji form; high-frequency news word.
Rarely used kanji form.
Compound of 机 (desk) and 上 (on, above). The figurative sense developed from the idea of something that exists only on a desk (i.e., in theory or on paper) rather than in practice.