Single User - Contiguous Storage

• Single user program in memory - and size of program fits memory
• Part of the memory held the operating system, the remainder the user program
• OS protected from user programs (to prevent user program overwriting OS code)
• OS protection by the user of a single boundary register built into the CPU
• Boundary register checked on each storage request
• However, if the user needs to use certain OS features (which it definitely will), use OS features through a kernel or supervisor call
• The size of programs in memory is restricted by the space available

What if multiple jobs active in memory simultaneously ?
Need for protection from each other and protection of OS