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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 Users Application Software System Software Hardware 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 OS CPU RAM HDD DOS 6.22 4 KHz 512 KB 5 MB Windows 3.0 12 KHz 3 MB 14 MB Windows 95 12 KHZ 4 MB 35 MB Windows 98 66 MHz 16MB 205 MB Windows ME 150 MHz 32 MB 480 MB Windows XP 233 MHz 64 MB 1.5 GB 1 GB / 2 GB 16 GB / 20 GB 32-bit/64-bit 32-bit/64-bit Windows Vista, 7,8,10 1 GHz http://www.osfiles.com/index.htm