Simple OS, MS-DOS Layer Structure, More complex OS: Multiple Apps
In This Topic & Blog Having Any Query Then Post your Comment and Suggestion Below
Simple OS: What if only one application?• Examples:
– Very early computers
– Early PCs
– Embedded controllers (elevators, cars, etc)
• OS becomes just a library of standard
services
– Standard device drivers
– Interrupt handlers
– Math libraries
MS-DOS Layer Structure
Application Program
Resident System Program
MS-DOS Device Drivers
ROM BIOS Device Drivers
More thoughts on Simple OS
• What about Cell-phones, etc?
– Is this organization enough?
– What about an Android or iPhone phone?
• Can OS be encoded in ROM/Flash ROM?
• Does OS have to be software?
– Can it be Hardware?
– Custom Chip with predefined behavior
– Are these even OSs?
More complex OS: Multiple Apps
• Full Coordination and Protection
– Manage interactions between different users
– Multiple programs running simultaneously
– Multiplex and protect Hardware Resources
• CPU, Memory, I/O devices like disks, printers, etc
• Facilitator
– Still provides Standard libraries, facilities
• Would this complexity make sense if there
were only one application that you cared
about?
Example: Protecting Processes from Each Other
• Problem: Run multiple applications in such a way
that they are protected from one another
• Goal:
– Keep User Programs from Crashing OS
– Keep User Programs from Crashing each other
– [Keep Parts of OS from crashing other parts?]
• (Some of the required) Mechanisms:
– Address Translation
– Dual Mode Operation
• Simple Policy:
– Programs are not allowed to read/write memory of
other Programs or of Operating System