Problems With The Counter Machine Model
- The problems are discussed in detail in the article Random access machine. The problems fall into two major classes and a third "inconvenience" class:
(1) Unbounded capacities of registers versus bounded capacities of state-machine instructions: How will the machine create constants larger than the capacity of its finite state machine?
(2) Unbounded numbers of registers versus bounded numbers of state-machine instructions: How will the machine access registers with address-numbers beyond the reach/capability of its finite state machine?
(3) The fully reduced models are cumbersome:
Shepherdson and Sturgis (1963) are unapologetic about their 6-instruction set. They have made their choice based on "ease of programming... rather than economy" (p. 219 footnote 1).
Shepherdson and Sturgis' instructions ( indicates "contents of register r"):
-
- INCREMENT ( r ) ; +1 → r
- DECREMENT ( r ) ; -1 → r
- CLEAR ( r ) ; 0 → r
- COPY ( rs to rd ) ; → rd
- JUMP-UNCONDITIONAL to instruction Iz
- JUMP IF =0 to instruction Iz
Minsky (1967) expanded his 2-instruction set { INC (z), JZDEC (r, Iz) } to { CLR (r), INC (r), JZDEC (r, Iz), J (Iz) } before his proof that a "Universal Program Machine" can be built with only two registers (p. 255ff).
Read more about this topic: Counter Machine
Famous quotes containing the words problems, counter, machine and/or model:
“The proper method of philosophy consists in clearly conceiving the insoluble problems in all their insolubility and then in simply contemplating them, fixedly and tirelessly, year after year, without any hope, patiently waiting.”
—Simone Weil (19091943)
“Family traditions counter alienation and confusion. They help us define who we are; they provide something steady, reliable and safe in a confusing world.”
—Susan Lieberman (20th century)
“All day long the machine waits: rooms,
stairs, carpets, furniture, people
those people who stand at the open windows like objects
waiting to topple.”
—Anne Sexton (19281974)
“Your home is regarded as a model home, your life as a model life. But all this splendor, and you along with it ... its just as though it were built upon a shifting quagmire. A moment may come, a word can be spoken, and both you and all this splendor will collapse.”
—Henrik Ibsen (18281906)