Operating System Overview: Understanding the Role and Components of an OS, Slides of Computer Science

Download Operating System Overview: Understanding the Role and Components of an OS and more Slides Computer Science in PDF only on Docsity! OPERATING SYSTEMS OVERVIEW Docsity.com WHAT IS AN OPERATING SYSTEM? • An interface between users and hardware - an environment "architecture” • Allows convenient usage; hides the tedious stuff • Allows efficient usage; parallel activity, avoids wasted cycles • Provides information protection • Gives each user a slice of the resources • Acts as a control program. OPERATING SYSTEM OVERVIEW Docsity.com The CPU is wasted if a job waits for I/O. This leads to: • Multiprogramming ( dynamic switching ). While one job waits for a resource, the CPU can find another job to run. It means that several jobs are ready to run and only need the CPU in order to continue. CPU scheduling is the subject of Chapter 6. All of this leads to: • memory management • resource scheduling • deadlock protection which are the subject of the rest of this course. OPERATING SYSTEM OVERVIEW Components Docsity.com Other Characteristics include: • Time Sharing - multiprogramming environment that's also interactive. • Multiprocessing - Tightly coupled systems that communicate via shared memory. Used for scientific applications. Used for speed improvement by putting together a number of off- the-shelf processors. • Distributed Systems - Loosely coupled systems that communicate via message passing. Advantages include resource sharing, speed up, reliability, communication. • Real Time Systems - Rapid response time is main characteristic. Used in control of applications where rapid response to a stimulus is essential. OPERATING SYSTEM OVERVIEW Characteristics Docsity.com OPERATING SYSTEM OVERVIEW Characteristics Interrupts: • Interrupt transfers control to the interrupt service routine generally, through the interrupt vector, which contains the addresses of all the service routines. • Interrupt architecture must save the address of the interrupted instruction. • Incoming interrupts are disabled while another interrupt is being processed to prevent a lost interrupt. • A trap is a software-generated interrupt caused either by an error or a user request. • An operating system is interrupt driven. Docsity.com OPERATING SYSTEM OVERVIEW Hardware Support This is O.S. Bookkeeping. These structures are necessary to keep track of IO in progress. Docsity.com Very fast storage is very expensive. So the Operating System manages a hierarchy of storage devices in order to make the best use of resources. In fact, considerable effort goes into this support. OPERATING SYSTEM OVERVIEW Storage Hierarchy Fast and Expensive Slow an Cheap Docsity.com OPERATING SYSTEM Storage OVERVIEW Hierarchy Performance: Level 1 2 3 4 Name registers cache main memory disk storage Typical size <1KB > 16 MB > 16 GB > 100 GB Implementation custom memory with | on-chip or off-chip] CMOS DRAM magnetic disk technology multiple ports, CMOS | CMOS SRAM Access time (ns) 0.25 - 0.5 ORS 5) 80 — 250 5,000.000 Bandwidth (MB/sec) | 20,000 — 100,000 5000 - 10,000 1000 - 5000 20-150 Managed by compiler hardware operating system | operating system Backed by cache main memory disk CD or tape Docsity.com Memory A user program can only access its own logical memory. For instance, it can't modify supervisor code. Depends on an address translation scheme such as that shown here. OPERATING SYSTEM OVERVIEW Protection Docsity.com CPU A clock prevents programs from using all the CPU time. This clock causes an interrupt that causes the operating system to gain control from a user program. OPERATING SYSTEM OVERVIEW Protection For machines connected together, this protection must extend across: Shared resources, Multiprocessor Architectures, Clustered Systems The practice of this is called “distributed operating systems”. Docsity.com WRAPUP We’ve completed our first overview of an Operating System – this was the equivalent of a Satellite picture. The next view will be at the level of a high flying plane. After that, we’ll be at ground level, looking at pieces in detail. OPERATING SYSTEM OVERVIEW Docsity.com