Use of a system call to perform io silberschatz

Use of A System Call to Perform I/O
Silberschatz, Galvin and Gagne  2002 2.22 Operating System Concepts
Memory Protection
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Must provide memory protection at least for the interrupt
vector and the interrupt service routines.
■
In order to have memory protection, add two registers
that determine the range of legal addresses a program
may access:
✦
Base register – holds the smallest legal physical memory
address.
✦
Limit register – contains the size of the range
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Memory outside the defined range is protected.

Silberschatz, Galvin and Gagne  2002 2.23 Operating System Concepts
Use of A Base and Limit Register
Silberschatz, Galvin and Gagne  2002 2.24 Operating System Concepts
Hardware Address Protection

Silberschatz, Galvin and Gagne  2002 2.25 Operating System Concepts
Hardware Protection
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When executing in monitor mode, the operating system
has unrestricted access to both monitor and user ’ s
memory.
■
The load instructions for the base and limit registers are
privileged instructions.
Silberschatz, Galvin and Gagne  2002 2.26 Operating System Concepts
CPU Protection
■
Timer – interrupts computer after specified period to
ensure operating system maintains control.
✦
Timer is decremented every clock tick.
✦
When timer reaches the value 0, an interrupt occurs.
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Timer commonly used to implement time sharing.
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Time also used to compute the current time.
■
Load-timer is a privileged instruction.

Silberschatz, Galvin and Gagne  2002 2.27 Operating System Concepts
Network Structure
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Local Area Networks (LAN)
■
Wide Area Networks (WAN)
Silberschatz, Galvin and Gagne  2002 2.28 Operating System Concepts
Local Area Network Structure

Silberschatz, Galvin and Gagne  2002 2.29 Operating System Concepts
Wide Area Network Structure