The Abstraction: Address Spaces

In the early days, building computer systems was easy. Why, you ask? Because users didn’t expect much. It is those darned users with their expectations of “ease of use”, “high performance”, “reliability”, etc., that really have led to all these headaches. Next time you meet one of those computer users, thank them for all the problems they have caused. 13.1 Early Systems From the perspective of memory, early machines didn’t provide much of an abstraction to users. Basically, the physical memory of the machine looked something like what you see in Figure 13.1. The OSwas a set of routines (a library, really) that sat inmemory (start-ing at physical address 0 in this example), and there would be one run-ning program (a process) that currently sat in physical memory (starting at physical address 64k in this example) and used the rest of memory. There were few illusions here, and the user didn’t expect much from the OS. Life was sure easy for OS developers in those days, wasn’t it? ma