ZAPP

Zero Assignment Parallel Processor. A virtual tree machinearchitecture in which a process tree is dynamically mappedonto a fixed, strongly connected network of processorscommunicating by message passing. The basic operation of eachnode is to apply a divide and conquer function which takesfour arguments: (1) a function 'primitive' which takes aproblem description (PD) and returns true if it can be solvedwithout division, (2) a function 'solve' which takes aprimitive PD and returns its solution, (3) a function 'divide'which takes a PD and returns a list of PDs of smaller problemsand (4) a function 'combine' which returns the solution to aproblem by combining a list of solutions of subproblems.

Each node has a copy of the code and one is given the initialproblem description. Task distribution is by process stealingin which a process constructs a descriptor for each subtaskand idle (lightly loaded) processors can steal a descriptorfrom a physically connected neighbour.