Operating Systems

Categories of Software System Software –Operating Systems (OS) –Language Translators –Utility Programs Application Software

Operating Systems It is the job of the operating system to manage the computers resources and control the execution of programs. Computer resources include –memory –device drivers for peripheral devices The OS is the interface between the hardware and the user/application program.

Layers of interaction Hardware System Software Application Software Users

OS Evolution Computer Operators, No OS Basic OS Multi-program Task switching Multi-tasking Preemptive Multi-tasking

Computer Operators, No OS Programs were load and run by the Computer Operator. Computer operator –Specified the memory locations to load a program and data –Specified the starting memory location for a program –Pressed the run button to run the program

Basic OS User manually started programs The OS handled the memory management. The OS handled disk management e.g. DOS = Disk Operating System

Multi-Program Multiple programs were loaded into memory at the same time. Only one program could run at any given time. User would manually switch between program. e.g. Mac System 1(a GUI interface)

Task Switching Allow the OS to switch between programs Each program needed to run to completion or be halted by the user before the OS would switch to the next program. Keep in mind that the CPU could only run one program at any given time.

Multi-tasking Gives the illusion that multiple programs are running at one time. A second is divided up into time slices (e.g. a millisecond) and each program is allowed to run for a time slice in a round robin fashion. If two program took 5 minutes each to run they would now both complete in 10 minutes.

Process & I/O bound It was observed that a running program may be in one of two states: –Processor (CPU) bound Program is running as fast as the CPU can execute its commands –I/O bound Program is waiting for input from a device, or Program is waiting to output to a device, or Program is waiting for an event to occur

Preemptive Multi-tasking Rather than giving each program its time slice the OS looks at the program state. –If program ready to run it gets it slice. –If program is not ready it is skipped. Since many programs spend most of their time an I/O bound state throughput can be significantly increased.

Common Operating Systems CP/M DOS Windows 3.1 Windows 95 Windows NT Windows Vista Windows 7, 8, 10 OS/2 System 7, 8, 9 Mac OSX Linux UNIX VMS VM/CMS

More CPU / RAM / HDD OSCPURAMHDD DOS KHz512 KB5 MB Windows KHz3 MB14 MB Windows 9512 KHZ4 MB35 MB Windows 9866 MHz16MB205 MB Windows ME150 MHz32 MB480 MB Windows XP233 MHz64 MB1.5 GB Windows Vista, 7,8,101 GHz1 GB / 2 GB16 GB / 20 GB 32-bit/64-bit