ajaynitt/OperatingSystem.cpp

## OperatingSystem.cpp
Main memory and the registers built into the processor itself are the only
storage that the CPU can access directly

Registers that are built into the CPU are generally accessible within one
cycle of the CPU clock

A base and a limit register define a logical address space

We can provide this protection by using two registers, usually
a base and a limit

The base register is now called a relocation register.
The value in the relocation register is added to every address generated by a
user process at the time it is sent to memory

The memory-mapping
hardware converts logical addresses into physical addresses.

The run-time mapping from virtual to physical addresses is done by a
hardware device called the memory-management unit (MMU).

For efficient CPU utilization, we want the execution time for each process
to be long relative to the swap time

The relocation register contains the value of the
smallest physical address; the limit register contains the range of logical
addresses

VIMU maps the logical address dynamically by adding the value in the relocation
register

When the CPU scheduler selects a process for execution, the dispatcher
loads the relocation and limit registers with the correct values as part of the
context switch. Because every address generated by the CPU is checked against
these registers, we can protect both the operating system and the other users'
programs and data from being modified by this running process.


If a device driver (or other operating-system service)
is not commonly used, we do not want to keep the code and data in memory, as
we might be able to use that space for other purposes. Such code is sometimes
called transient operating-system code; it comes and goes as needed

given N allocated blocks, another 0.5 N blocks will be lost to fragmentation.
That is, one-third of memory may be unusable! This property is known as the
50-percent rule
	Main memory and the registers built into the processor itself are the only
	storage that the CPU can access directly

	Registers that are built into the CPU are generally accessible within one
	cycle of the CPU clock

	A base and a limit register define a logical address space

	We can provide this protection by using two registers, usually
	a base and a limit

	The base register is now called a relocation register.
	The value in the relocation register is added to every address generated by a
	user process at the time it is sent to memory

	The memory-mapping
	hardware converts logical addresses into physical addresses.

	The run-time mapping from virtual to physical addresses is done by a
	hardware device called the memory-management unit (MMU).

	For efficient CPU utilization, we want the execution time for each process
	to be long relative to the swap time

	The relocation register contains the value of the
	smallest physical address; the limit register contains the range of logical
	addresses

	VIMU maps the logical address dynamically by adding the value in the relocation
	register

	When the CPU scheduler selects a process for execution, the dispatcher
	loads the relocation and limit registers with the correct values as part of the
	context switch. Because every address generated by the CPU is checked against
	these registers, we can protect both the operating system and the other users'
	programs and data from being modified by this running process.


	If a device driver (or other operating-system service)
	is not commonly used, we do not want to keep the code and data in memory, as
	we might be able to use that space for other purposes. Such code is sometimes
	called transient operating-system code; it comes and goes as needed

	given N allocated blocks, another 0.5 N blocks will be lost to fragmentation.
	That is, one-third of memory may be unusable! This property is known as the
	50-percent rule