Tiêu đề OS-Material.pdf ✅

UNIT-1 NOTES Operating Systems Fundamentals Page 2 Operating System Definition • An operating system as a resource allocator. A computer system has many resources that may be required to solve a problem: CPU time, memory space, file-storage space, I/O devices, and so on. The operating system acts as the manager of these resources. • Decides between conflicting requests for efficient and fair resource use • OS is a control program A control program manages the execution of user programs to prevent errors and improper use of the computer. It is especially concerned with the operation and control of I/O devices. • “OS is the one program running at all times on the computer” is the kernel. Everything else is either a system program (ships with the operating system) or an application program • System programs which are associated with the operating system but are not part of the kernel, and application programs which include all programs not associated with the operation of the system.) Computer Startup • bootstrap program is loaded at power-up or reboot • Typically stored in ROM or EPROM, generally known as firmware • Initializes all aspects of system • Loads operating system kernel and starts execution • Once the kernel is loaded and executing, it can start providing services to the system and its users. Some services are provided outside of the kernel, by system programs that are loaded into memory at boot time to become system processes, or system daemons that run the entire time the kernel is running. On UNIX, the first system process is “init,” and it starts many other daemons. Once this phase is complete, the system is fully booted, and the system waits for some event to occur. Computer System Organization • Computer-system operation • One or more CPUs, device controllers connect through common bus providing access to shared memory • Concurrent execution of CPUs and devices competing for memory cycles

UNIT-1 NOTES Operating Systems Fundamentals Page 4 Interrupt Timeline I/O Structure • A general-purpose computer system consists of CPUs and multiple device controllers that are connected through a common bus. Each device controller is in charge of a specific type of device. Depending on the controller, more than one device may be attached. For instance, seven or more devices can be attached to the small computer- systems interface (SCSI) controller. • 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 rest of the operating system with a uniform interface to the device. • To start an I/O operation, the device driver loads the appropriate registers within the device controller. The device controller, in turn, examines the contents of these registers to determine what action to take (such as “read a character from the keyboard”). The controller starts the transfer of data from the device to its local buffer. Once the transfer of data is complete, the device controller informs the device driver via an interrupt that it has finished its operation. The device driver then returns control to the operating system, possibly returning the data or a pointer to the data if the operation was a read. For other operations, the device driver returns status information. • System call – request to the operating system to allow user to wait for I/O completion • Device-status table contains entry for each I/O device indicating its type, address, and state