1. horizontal encoding An instruction set where each field a bit or group of bits in an instruction word controls some functional unit or gate directly, as opposed to vertical encoding where instruction fields are decoded by hard-wired logic or microcode to produce the control signals. Horizontal encoding allows all possible combinations of control signals and therefore operations to be expressed as instructions whereas vertical encoding uses a shorter instruction word but can only encode those combinations of operations built into the decoding logic. An instruction set may use a mixture of horizontal and vertical encoding within each instruction. Because an architecture using horizontal encoding typically requires more instruction word bits it is sometimes known as a very long instruction word VLIW architecture.
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