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In a stack machine, the operands used in the instructions are always at a known offset (set in the stack pointer), from a fixed location (the bottom of the stack, which in a hardware design might always be at memory location zero), saving precious in-cache or in-CPU storage from being used to store quite so many memory addresses or index ...
A stack machine has most or all of its operands on an implicit stack. Special purpose instructions also often lack explicit operands; for example, CPUID in the x86 architecture writes values into four implicit destination registers.
The simple model provided in a stack-oriented language allows expressions and programs to be interpreted simply and theoretically evaluated much faster, since no syntax analysis needs to be done but lexical analysis. The way such programs are written facilitates being interpreted by machines, which is why PostScript suits printers well for its use.
Each instruction specifies some number of operands (registers, memory locations, or immediate values) explicitly. Some instructions give one or both operands implicitly, such as by being stored on top of the stack or in an implicit register. If some of the operands are given implicitly, fewer operands need be specified in the instruction.
However, it is possible to construct Turing complete machines using an instruction based on other arithmetic operations, e.g., addition. For example, one variation known as DLN (Decrement and jump if not zero) has only two operands and uses decrement as the base operation. For more information see Subleq derivative languages .
Machine code is the form in which code that can be directly executed is stored on a computer. It consists of machine language instructions, stored in memory, that perform operations such as moving values in and out of memory locations, arithmetic and Boolean logic, and testing values and, based on the test, either executing the next instruction in memory or executing an instruction at another ...
Some machines use a stack for arithmetic and logical operations; operands are pushed onto the stack, and arithmetic and logical operations act on the top one or more items on the stack, popping them off the stack and pushing the result onto the stack. Machines that function in this fashion are called stack machines. A number of mainframes and ...
Most stack machines are, infact two-stack machines. One for operands and one for loop counters. It also happens that the loop counter stack is used for return values in most stack machines, because its a convienant place for them. Look at Patriot Scientific, or Forth Machines, or varius Postscript processors found in many printers...