9 - A Model of Computation GapFill

A Turing machine can be described as an abstract computer containing  all possible programsa re-writable programa single fixed programa standard-issue program.  The machine can, at any time, be in one of a finite number of  conditionsprotocolsstatesthreads, and can   composedecomposemergetransition to another, depending on the  nature of the programCPU instruction setinput from the useravailable memory.  Another component is an infinite  drivediskprogramtape, divided into squares or cells, each of which contains a character from a finite set of permissible symbols.  A(n)  write headsensing read-write headiteratorread head travels along this, one such cell at a time.  A control unit, which stores instructions, completes this theoretical device, and it acts upon the character within the cell, according to these instructions.  These instructions are referred to as  composition rulestransition codesmerge rulestransition rules.