OS_from_scratch_Overview

==> Overview

* An Operating system is software that manages a computer's hardware.

* It also provides a bases for application programs and acts as an intermediary between the computer used and the computer hardware.

==> What Operating Systems Do

 A computer system can be divided roughly in four components:
 	- the hardware
 	- the operating system
 	- the application programs
 	- a User
 	
Hardware - the central processing unit (CPU)
	   the memory
	   the input/output(I/O) devices
																																																															application programs - such as word processors
		        spreadsheets
		        compilers
		        web browsers
		        
* Exploring OS from two viewpoints:
			- From the user perspective
			- From the system perspective
			
	-> User View: User with a laptop or in front of a PC consisting monitor, keyboard and mouse. Such a syustem is designed for one user to monopolize its resources.
	The goal is to maximize the work(or play) that the user is performing.
	Designed for ease os use, with some attention paid to performance and security and none paid to resource utilization - how various hardware and softwware resources are shared.
	
	-> System View:
		- From the computer's point of view, the operating system is the program most intimately involved with the hardware. In this context, we can view an operating system as a "resource allocator". 	
		- A computer system has many resources that may be required to solve a problem: CPU time, memory spacce, storage space, I/O devices, and so on.
		
		- A control program manages the execution of user programs to prevent errors and improper use of the computer. It is espcially concerned with the operation and control of I/O devices 			   																																	
	
==> Computer-System Organization	
	- A modern general-purpose computer system consists of one or more CPUs and a number of device controller connected through a common bus that provides access between components and shared memory. Each device controller is in charge of a specific type of device (for example, a disk drive, audio device, or graphics display)
	
	- Depending on the controller, more than one device may be attached. For instance, one system USB port can connect to a USB hub, to which several devices can connect
	
	- A device controller maintains some local buffer storage and a set of special-purpose registers

	- The device controller is responsible for moving the data between the peripheral devices that it controls and its local buffer storage
	
	- Typically, operating systems have a device driver for each device controller. This device driver understands the device controller and provides the operating system with a uniform interface to the device.
	- The CPU and the device controllers can execute in parallel, competing for memory cycles. To ensure orderly access to the shared memory, a memory controller synchronizes access to memory
	- 3 key aspects of the system: 1] Interrupts (which alert the CPU to events that require attention)
				       2] Storage structure
				       3] I/O structure