A vertical microinstruction is a microinstruction that specifies one of a sequence of operations needed to carry out a machine language instruction. Vertical microinstructions are short, 12 to 24 bit instructions. They're called vertical because they are normally listed vertically on a page. These 12 to 24 bit microinstructions instructions are required to carry out a single machine language instruction. In addition to vertical microinstructions, there are horizontal and diagonal microinstructions as well.