(SECD machine) The first abstract machine for reducing lambda-calculus expressions, invented by P. J. Landin. The machine has four registers holding pointers to linked lists operated as push-down stacks which hold the information required for the evaluation of an expression. The registers point to (1) Stack which holds the arguments of partially evaluated expressions and results of completely evaluated ones, (2) Environment where the current expression being evaluated is stored, (3) Control which holds the machine instructions that manipulate the contents of the four registers that represent the expression being evaluated, (4) Dump on which the state of the machine is temporarily saved during the evaluation of expressions. See also Lispkit.