A generating function approach to queueing network analysis of multiprogrammed computers

Modern multiprogrammed computing systems are dis t inguished by t h e i r a b i l i t y t o handle a number of jobs concurrent ly . When one job , r e s iden t i n such a system, performs an I/O, it r e l i n quishes i t s hold on the CPU, and another job takes over the CPU while t h e f i r s t awai ts completion o f t he I/O. Operations of this type r a i s e quest ions as t o j u s t how many jobs should be r e s iden t i n the computer, s ince it i s not a p r i o r i c l e a r j u s t how much degradation the jobs s u f f e r when t h e r e a r e many of them contending and i n t e r f e r i n g with each o t h e r i n obta in ing access t o the var ious processing devices of t h e computer. It is d i f f i c u l t t o judge the e f f e c t s of replacing one device by another with d i f f e r e n t speed, o r of adding o r sub t r ac t ing a device.