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CCS 2124 OPERATING SYSTEMS I
Introduction
References:
- Abraham Silberschatz, Greg Gagne, and Peter Baer Galvin, "Operating System Concepts, Ninth Edition ", Chapter 1
- https://www2.cs.uic.edu/~jbell/CourseNotes/OperatingSystems/
Here we look at Operating Systems from a number of different viewpoints. No one view really shows the complete picture, but by looking from a number of different views, we can get a pretty good overall picture of what operating systems are all about.
1.1 What Operating Systems Do - For Users, For Applications, etc.?
Figure 1.1 - Abstract view of the components of a computer system
- Computer = HW + OS + Apps + Users
- OS serves as interface between HW and ( Apps & Users )
- OS provides services for Apps & Users
- OS manages resources (Government model, it doesn't produce anything.)
- Debates about what is included in the OS - Just the kernel, or everything the vendor ships? (Consider the distinction between system applications and 3rd party or user apps.)
1.2 Computer-System Organization - What are all the parts, and how do they fit
together?
Figure 1.2 - A modern computer system
1.2.1 Computer-System Operation
- Bootstrap program
- Shared memory between CPU and I/O cards
- Time slicing for multi-process operation
- Interrupt handling - clock, HW, SW
- Implementation of system calls
Figure 1.3 - Interrupt timeline for a single process doing output
1.2.2 Storage Structure
- Main memory ( RAM ) o Programs must be loaded into RAM to run. o Instructions and data fetched from RAM into registers. o RAM is volatile o "Medium" size and speed
- Other electronic (volatile) memory is faster, smaller, and more expensive per bit: o Registers o CPU Cache
- Non-volatile memory ("permanent" storage) is slower, larger, and less expensive per bit: o Electronic disks o Magnetic disks
- Increased reliability o Failure of a CPU slows system, doesn't crash it. o Redundant processing provides system of checks and balances. ( e.g. NASA )
Figure 1.6 - Symmetric multiprocessing architecture
Figure 1.7 - A dual-core design with two cores placed on the same chip
1.3.3 Clustered Systems
- Independent systems, with shared common storage and connected by a high-speed LAN, working together.
- Special considerations for access to shared storage are required, (Distributed lock management), as are collaboration protocols.
Figure 1.8 - General structure of a clustered system
1.4 Operating-System Structure
A time-sharing (multi-user multi-tasking) OS requires:
- Memory management
- Process management
- Job scheduling
- Resource allocation strategies
- Swap space / virtual memory in physical memory
- Interrupt handling
- File system management
- Protection and security
- Inter-process communications
Figure 1.9 - Memory layout for a multiprogramming system
1.5.2 Timer
- Before the kernel begins executing user code, a timer is set to generate an interrupt.
- The timer interrupt handler reverts control back to the kernel.
- This assures that no user process can take over the system.
- Timer control is a privileged instruction, (requiring kernel mode.)
1.6 Process Management
An OS is responsible for the following tasks with regards to process management:
- Creating and deleting both user and system processes
- Ensuring that each process receives its necessary resources, without interfering with other processes.
- Suspending and resuming processes
- Process synchronization and communication
- Deadlock handling
1.7 Memory Management
An OS is responsible for the following tasks with regards to memory management:
- Keeping track of which blocks of memory are currently in use, and by which processes.
- Determining which blocks of code and data to move into and out of memory, and when.
- Allocating and deallocating memory as needed. (E.g. new, malloc)
1.8 Storage Management
1.8.1 File-System Management
An OS is responsible for the following tasks with regards to filesystem management:
- Creating and deleting files and directories
- Supporting primitives for manipulating files and directories. (open, flush, etc.)
- Mapping files onto secondary storage.
- Backing up files onto stable permanent storage media.
1.8.2 Mass-Storage Management
An OS is responsible for the following tasks with regards to mass-storage management:
- Free disk space management
- Storage allocation
Note the trade-offs regarding size, speed, longevity, security, and re-writability between different mass storage devices, including floppy disks, hard disks, tape drives, CDs, DVDs, flash disks etc.
1.8.3 Caching
- There are many cases in which a smaller higher-speed storage space serves as a cache, or temporary storage, for some of the most frequently needed portions of larger slower storage areas.
- The hierarchy of memory storage ranges from CPU registers to hard drives and external storage. (See table below.)
- The OS is responsible for determining what information to store in what level of cache, and when to transfer data from one level to another.
- The proper choice of cache management can have a profound impact on system performance.
- Data read in from disk follows a migration path from the hard drive to main memory, then to the CPU cache, and finally to the registers before it can be used, while data being written follows the reverse path. Each step (other than the registers) will typically fetch more data than is immediately needed, and cache the excess in order to satisfy future requests faster. For writing, small amounts of data are frequently buffered until there is enough to fill an entire "block" on the next output device in the chain.
- The issues get more complicated when multiple processes (or worse multiple computers) access common data, as it is important to ensure that every access reaches the most up-to-date copy of the cached data (amongst several copies in different cache levels.)
Figure 1.11 - Performance of various levels of storage
Figure 1.14 - Doubly linked list
Figure 1.15 - Circularly linked list
1.10.2 Trees
Figure 1.16 - Binary search trees
1.10.3 Hash Functions and Maps
Figure 1.17 - Hash map
1.10.4 Bitmaps
- A string of 1s and 0s used to keep track of the boolean state of a collection of objects, such as the free state of blocks on a disk or pages in memory.
1.11 Computing Environments
1.11.1 Traditional Computing
1.11.2 Mobile Computing
- Computing on small handheld devices such as smart phones or tablets. (As opposed to laptops, which still fall under traditional computing.)
- May take advantage of additional built-in sensors, such as GPS, tilt, compass, and inertial movement.
- Typically connect to the Internet using wireless networking (IEEE 802.11) or cellular telephone technology.
- Limited in storage capacity, memory capacity, and computing power relative to a PC.
- Generally uses slower processors that consume less battery power and produce less heat.
- The two dominant OSes today are Google Android and Apple iOS.
1.11.3 Distributed Systems
- Distributed Systems consist of multiple, possibly heterogeneous, computers connected together via a network and cooperating in some way, form, or fashion.
- Networks may range from small tight LANs to broad reaching WANs. o WAN = Wide Area Network, such as an international corporation o MAN =Metropolitan Area Network, covering a region the size of a city for example. o LAN =Local Area Network, typical of a home, business, single-site corporation, or university campus. o PAN = Personal Area Network, such as the Bluetooth connection between your PC, phone, headset, car, etc.
- Network access speeds, throughputs, reliabilities, are all important issues.
- OS view of the network may range from just a special form of file access to complex well-coordinated network operating systems.
- Shared resources may include files, CPU cycles, RAM, printers, and other resources.
1.11.4 Client-Server Computing
- A defined server provides services (HW or SW) to other systems which serve as clients. (Technically clients and servers are processes, not HW, and may co-exist on the same physical computer.)
- A process may act as both client and server of either the same or different resources.
- Served resources may include disk space, CPU cycles, time of day, IP name information, graphical displays (X Servers), or other resources.
- Virtualization can slow down program that have to run through the VMM, but can also speed up some things if virtual hardware can be accessed through a cache instead of a physical device.
- Depending on the implementation, programs can also run simultaneously on the native OS, bypassing the virtual machines.
Figure 1.20 - VMWare
- To run Linux on a Windows system using VMware, follow these steps:
- Download the free "VMware Player" tool from http://www.vmware.com/download/player and install it on your system
- Choose a Linux version from among hundreds of virtual machine images at http://www.vmware.com/appliances
- Boot the virtual machine within VMware Player.
1.11.7 Cloud Computing
- Delivers computing, storage, and applications as a service over a network.
- Types of cloud computing: o Public cloud - Available to anyone willing to pay for the service. o Private cloud - Run by a company for internal use only. o Hybrid cloud - A cloud with both public and private components. o Software as a Service - SaaS - Applications such as word processors available via the Internet o Platform as a Service - PaaS - A software stack available for application use, such as a database server
o Infrastructure as a Service - IaaS - Servers or storage available on the Internet, such as backup servers, photo storage, or file storage. o Service providers may provide more than one type of service
- Clouds may contain thousands of physical computers, millions of virtual ones, and petabytes of total storage.
- Web hosting services may offer (one or more) virtual machine(s) to each of their clients.
Figure 1.21 - Cloud computing
1.11.8 Real-Time Embedded Systems
- Embedded into devices such as automobiles, climate control systems, process control, and even toasters and refrigerators.
- May involve specialized chips, or generic CPUs applied to a particular task. (Consider the current price of 80286 or even 8086 or 8088 chips, which are still plenty powerful enough for simple electronic devices such as kids’ toys.)
- Process control devices require real-time (interrupt driven) OSes. Response time can be critical for many such devices.
1.12 Open-Source Operating Systems
- ( For more information on the Flourish conference held at UIC on the subject of Free Libre and Open Source Software , visit http://www.flourishconf.com )
- BSD UNIX is not open-source, however, because a license is still needed from ATT.
- In spite of various lawsuits, there are now several versions of BSD UNIX, including Free BSD, NetBSD, OpenBSD, and DragonflyBSD
- The source code is located in /usr/src.
- The core of the Mac operating system is Darwin, derived from BSD UNIX, and is available at http://developer.apple.com/opensource/index.html
1.13.4 Solaris
- Solaris is the UNIX operating system for computers from Sun Microsystems.
- Solaris was originally based on BSD UNIX, and has since migrated to ATT SystemV as its basis.
- Parts of Solaris are now open-source, and some are not because they are still covered by ATT copyrights.
- It is possible to change the open-source components of Solaris, re-compile them, and then link them in with binary libraries of the copyrighted portions of Solaris.
- Open Solaris is available from http://www.opensolaris.org/os/
- Solaris also allows viewing of the source code online, without having to download and unpack the entire package.
1.13.5 Utility
- The free software movement is gaining rapidly in popularity, leading to thousands of ongoing projects involving untold numbers of programmers.
- Sites such as http://freshmeat.net/ and http://distrowatch.com/ provide portals to many of these projects.
