Y!89 uses a full, partly extended, width iterative [principal variation search](Principal_Variation_Search "Principal Variation Search") with [capture](Captures "Captures") and [promotion](Promotions "Promotions") [searches](Quiescence_Search "Quiescence Search") in [terminal nodes](Quiescent_Node "Quiescent Node"). The program is designed to be used in a cheap commercial environment, thus the work [memory](Memory "Memory") is still just 4 kbytes of [RAM](Memory#RAM "Memory"), and the good old [6502](6502 "6502") eight bit processor is used in tournaments emulated by the also commercially available [Turbo kit](6502#TK20 "6502"). The [search](Search "Search") is fast for a micro, and includes detection of [repeated positions](Repetitions "Repetitions") (actual as well as potential), and performs [extensions](Extensions "Extensions") for [check evasions](Check_Extensions "Check Extensions"), [passed pawn moves](Passed_Pawn_Extensions "Passed Pawn Extensions") and some king moves in [pawn endgames](Pawn_Endgame "Pawn Endgame").

Most of the [material](Material "Material") and [positional evaluation](Evaluation_of_Pieces "Evaluation of Pieces") is made [incrementally](Incremental_Updates "Incremental Updates") by the means of material value tables and [positional score boards](Piece-Square_Tables "Piece-Square Tables") for each piece type, created once for each position of the game with the computer to move. Some "absolute" evaluation is also done, e.g. for static evaluation of [unstoppable passed pawns](Unstoppable_Passer "Unstoppable Passer") and [pawn structure](Pawn_Structure "Pawn Structure").