be used as word processor or to run video games to change the program of such machineone has to replace the circuitry the first truly modern computer was the manchester mark it was distinguished from its predecessors by the fact that it was stored-program computer such computer stores (and manipulatesa sequence of instructionsand has set of elements that will execute any instruction in that sequence by creating an instruction-set architecture and detailing the computation as sequence of instructions ( program)we make highly flexible machine by treating those instructions in the same way as dataa stored-program machine can easily change the programand can do so under program control indeedthe heart of the computer then becomes program (called an interpreterthat can execute any legal set of instructionsand thus can be used to compute anything that one can describe using some basic set of instructions both the program and the data it manipulates reside in memory typically there is program counter that points to particular location in memoryand computation starts by executing the instruction at that point most oftenthe interpreter simply goes to the next instruction in the sequencebut not always in some casesit performs testand on the basis of that testexecution may jump to some other point in the sequence of instructions this is called flow of controland is essential to allowing us to write programs that perform complex tasks returning to the recipe metaphorgiven fixed set of ingredients good chef can make an unbounded number of tasty dishes by combining them in different ways similarlygiven small fixed set of primitive elements good programmer can produce an unbounded number of useful programs this is what makes programming such an amazing endeavor to create recipesor sequences of instructionswe need programming language in which to describe these thingsa way to give the computer its marching orders in the british mathematician alan turing described hypothetical computing device that has come to be called universal turing machine the machine had an unbounded memory in the form of tape on which one could write zeros and onesand some very simple primitive instructions for movingreadingand writing to the tape the church-turing thesis states that if function is computablea turing machine can be programmed to compute it the "ifin the church-turing thesis is important not all problems have computational solutions for exampleturing showed that it is impossible to write program that given an arbitrary programcall it pprints true if and only if will run forever this is known as the halting problem this computer was built at the university of manchesterand ran its first program in it implemented ideas previously described by john von neumann and was anticipated by the theoretical concept of the universal turing machine described by alan turing in