This thesis describes the design of a well mapped machine¹ for the language BCPL. Based on a generalized notion of stack machines the SLIM (Stack Language for Intermediate Machines) machine is described. As the acronym suggests, representation of BCPL programs in SLIM is in fact slim compared with other architectures. The utility of this measure for comparison with other architectures is discussed and some encouraging results presented. Apart from this result, some advance is made in the classical mode of porting BCPL programs. Normally the compiler produces OCODE from which INTCODE is generated. The BCPL SLIM compiler shortcuts this process by generating SLIM directly from the program tree thus dispensing with software corresponding to the OCODE to INTCODE translator. Translation of BCPL programs is thus simplified and speeded up. ¹by well mapped we mean that transformations in the high level language correspond closely to those in the low level machine representation. / Science, Faculty of / Computer Science, Department of / Graduate