Sistem operasi

Sebuah sistem operasi (OS) adalah sekumpulan software yang mengatur sumber daya di hardware komputer dan memberikan layanan bagi program komputer. Sistem Operasi adalah komponen penting dari sistem perangkat lunak dalam sebuah komputer. Program aplikasi biasanya membutuhkan sistem operasi untuk bisa berfungsi.

Sistem operasi time sharing menjadwal tugas agar dapat secara effisien menggunakan sistem. Hal ini termasuk menghitung alokasi biaya dari waktu processor, harddisk, printing dan berbagai sumber daya lainnya.

Untuk fungsi hardware seperti input dan output dan alokasi memory, sistem operasi berfungsi sebagai perantara antara program dengan komputer hardware. Meskipun demikian aplikasi dijalankan secara langsung oleh hardware dan biasanya akan melakukan sistem call ke fungsi di OS atau di interupsi oleh OS tersebut. Sistem operasi dapat di temukan di hampir semua alat yang mempunyai fungsi komputer mulai dari handphone, video game hingga super komputer dan web server.

Contoh sistem operasi modern termasuk Android, BSD, iOS, Linux, Mac OS X, Microsoft Windows, and IBM z/OS. Semuanya, kecuali Windows dan z/OS, mempunyai akar yang sama yaitu Unix

Tipe Sistem Operasi

Real-time

Sistem operasi real-time adalah sebuah sistem operasi multitasking yang ditujukan untuk menjalankan aplikasi real-time. Sistem Operasi real-time biasanya menspesialisasikan pada algoritma scheduling (penjadwalan) sehingga mereka dapat mencapai perilaku yang deterministik. Tujuan utama sebuah sistem operasi real-time adalah respons yang cepat dan dapat di prediksi untuk berbagai kejadian. Sistem operasi ini di rancang berdasarkan event-driven atau time-sharing atau kedua-nya. Sebuah sistem event-driven melakukan switching antar task berdasarkan prioritas atau kejadian (event) dari luar, sementara sistem operasi time-sharing melakukan switching antar task berbasis pada interupsi clock.

Multi-user

Sistem operasi multi-user memungkinkan banyak pengguna untuk mengakses sistem komputer pada saat yang sama. Sistem time-sharing dan server di Internet dapat dikategorikan sebagai sistem multi-user karena mereka memungkinkan banyak pengguna untuk mengakses komputer dengan cara berbagai waktu (sharing time). Sistem operasi single user hanya satu pengguna tapi dapat menjalankan multiple program pada saat yang sama.

Multi-tasking vs. single-tasking

Sebuah sistem operasi multi-tasking memungkinkan lebih dari satu program untuk berjalan pada satu saat, dilihat dari skala waktu manusia. Sebuah sistem single-tasking hanya dapat menjalankan satu program. Ada dua tipe Multi-tasking, yaitu: (1) pre-emptive dan (2) co-operative. Di pre-emptive multitasking, sistem operasi akan membagi CPU time dan mendedikasikan satu slot untuk setiap program. Di sistem operasi Unix-like, seperti, Solaris dan Linux, biasanya mendukung pre-emptive multitasking, seperti juga AmigaOS. Cooperative multitasking dapat dicapai dengan cara saling mengandalkan satu sama lain untuk memberikan waktu / slot time ke proses yang lain dengan aturan yang baku.

Sistem Terdistribusi

Sebuah sistem operasi terdistribusi mengatur sebuah kelompok dari komputer yang independen dan membuat mereka tampak seperti satu buah komputer. Dengan perkembangan jaringan komputer memungkinkan sambungan dan komunikasi satu sama lain untuk membangun distributed computing. Komputasi terdistribusi dilakukan oleh lebih dari satu mesin. Jika komputer dalam satu group bekerjasama, maka mereka akan membangun sebuah distributed system / sistem terdistribusi.

Sistem Embedded

Sistem operasi embedded di rancang untuk digunakan di sistem komputer embedded. Sistem operasi embedded di operasikan di mesin kecil seperti PDA. Sistem operasi ini dapat beroperasi dengan sumber daya yang sangat terbatas. Sistem operasi ini di rancang agar sangat kecil dan sangat effisien. Contoh dari sistem operasi embedded ini adalah OpenWRT.

Sejarah

Pada awalnya komputer dibuat untuk menjalankan sekumpulan single task, seperti calculator. Sistem operasi belum menampakan diri sampai awal 1960. Dasar fitur sistem operasi mulai dikembangkan tahun 1950, seperti fungsi monitor yang dapat secara automatis menjalankan program yang berbeda dalam rangka mempercepat processing. Fitur hardware di tambahkan untuk membuka kemungkinan untuk menggunakan runtime library, interrupsi, dan parallel processing. Pada saat PC menjadi populer di tahun 1980-an, sistem operasi yang dibuat untuk PC secara konsep sama dengan yang digunakan di komputer yang besar.

Di tahun 1940-an, sistem elektronik digital awal tidak mempunyai sistem operasi.Sistem elektronik pada masa itu di program menggunakan sekumpulan switch mekanik atau dengan kabel jumper di papan board. Sistem ini merupakan sistem special-purpose, sebagai contoh, untuk membuat tabel balistik untuk militer atau mengatur pencetakan slip gaji dari data di punch card. Sesudah komputer aplikasi umum yang programmable dibuat, bahasa mesin (terdiri dari kalimat yang terdiri dari digit 0 dan 1 di kartu punch card) di petkenalkan untuk mempercepat proses programming. OS/360 digunakan pada sebagian besar komputer mainframe IBM di awal tahun 1966, termasuk komputer yang menolong NASA untuk menerbangkan manusia ke bulan.

Di awal tahun 1950, sebuah komputer hanya dapat menjalankan satu program pada satu waktu. Setiap pengguna menggunakan sendiri komputer untuk waktu yang terbatas sesuai dengan jadwal waktu, dengan program dan data yang ada di punch card atau punch tape. Program akan di load ke komputer, dan komputer akan bekerja sampai program selesai atau crash. Program biasanya di debug melalui panel di depan menggunakan switch dan lampu panel.

Belakangan mesin-mesin ini dilengkapi dengan program library, yang di sambungkan (di link) di program user untuk membantu operasi tertentu, seperti, input, output, dan membuat kode komputer yang dapat dibaca manusia. Ini merupakan asal muasal sistem operasi modern. Akan tetapi, mesin masih menjalankan single job pada satu waktu.

Mainframe

Di tahun 1950, banyak fitur di pelopori di bidang sistem operasi, termasuk proses batch, interupsi input/output, buffering, multitasking, spooling, runtime library, link-loading, dan program untuk mengurut catatan di file. Fitur ini tidak dimasukan dalam software aplikasi sebagai pilihan bagi programmer, tapi dibuat sebagai sistem operasi yang terpisah yang digunakan oleh semua aplikasi. Di tahun 1959, sistem operasi SHARE di lepas sebagai utility integrated untuk IBM 704, selanjutnya di mainframe 709 dan 7090 walaupun kemudian digantikan oleh IBSYS/IBJOB di 709, 7090 dan 7094.

Selama tahun 1960, IBM OS/360 memperkenalkan konsep sebuah OS untuk semua produk, yang menjadi sangat penting untuk kesuksesan mesin System/360. Sistem operasi di mainframe IBM saat ini adalah turunan dari sistem awal dan aplikasi yang ditulis untuk OS/360 masih bisa berjalan di mesin yang modern.

OS/360 juga memelopori konsep yang menentukan bahwa sistem operasi akan mencatat semua penggunaan sumber daya, termasuk alokasi memori untuk program dan data, ruang file di harddisk, penguncian file saat update. Jika proses ini di putuskan karena berbagai alasan, semua sumber daya tersebut akan direklamasi oleh sisten operasi.

Alternatif sistem operasi CP-67 untuk S/360-67 memulai sebuah jalur pada sistem operasi IBM yang memfokuskan diri pada mesin virtual. Sistem operasi lainnya yang digunakan di seri mainframe IBM S/360 termasuk sistem yang dikembangkan sendiri oleh IBM: COS/360 (Compatibility Operating System), DOS/360 (Disk Operating System), TSS/360 (Time Sharing System), TOS/360 (Tape Operating System), BOS/360 (Basic Operating System), dan ACP (Airline Control Program), termasuk beberapa sistem non-IBM: MTS (Michigan Terminal System), MUSIC (Multi-User System for Interactive Computing), dan ORVYL (Stanford Timesharing System).

Control Data Corporation mengembangkan sistem operasi SCOPE di tahun 1960-an untuk batch processing. Bekerjasama dengan University of Minnesota, sistem operasi Kronos dan selanjutnya NOS dikembangkan pada tahun 1970-an, yang mendukung batch secara simultan dan penggunaan timesharing. Seperti sistem timesharing komersial lainnya, interfacenya merupakan extensi dari Dartmouth BASIC operating systems, salah satu usaha rintisan dalam timesharing dan bahasa pemrogramman. In akhir tahun 1970-an, Control Data dan University of Illinois mengembangkan sistem operasi PLATO, yang menggunakan display plasma panel dan jaringan time sharing jarak jauh. Plato termasuk cukup inovatif pada masanya, fitur seperti real-time chat, dan game grafis multi-user. Burroughs Corporation memperkenalkan B5000 di tahun 1961 dengan sistem operasi MCP, (Master Control Program). B5000 di rancang sebagai stack machine untuk mendukung bahasa tingkat tinggi tanpa bahasa mesin atau assembler, dan MCP adalah sistem operasi pertama yang ditulis secara exclusif dalam bahasa tingkat tinggi - ESPOL, sebuah dialek dari ALGOL. MCP juga memperkenalkan banyak innovasi baru, seperti implementasi komersial pertama untuk memory virtual. Dalam masa pengembangan AS400, IBM sempat mendekati Burroughs untuk membeli lisensi dari MCP agar dapat di jalankan di hardware AS400. Proposal IBM di tolak oleh manajemen Burroughs untuk melindungi produksi hardware mereka. MCP sampai hari ini masih digunakan di komputer Unisys ClearPath/MCP.

UNIVAC, pembuat komputer komersial pertama, memproduksi sistem operasi EXEC. Seperti halnya sistem mainframe awal, EXEC adalah sistem yang berorientasi batch yang mengatur drum magnetic, disk, card reader dan line printer. Di tahun 1970-an, UNIVAC membuat Real-Time Basic (RTB) system untuk mendukung time sharing skala besar, yang diturunkan Dartmouth BC system.

General Electric dan MIT mengembangkan General Electric Comprehensive Operating Supervisor (GECOS), yang memperkenalkan konsep keamanan yang berlapis. Setelah di akusisi oleh Honeywell, sistem operasi ini di beri nama General Comprehensive Operating System (GCOS).

Digital Equipment Corporation juga mengembangkan banyak sistem operasi untuk berbagai komputernya, termasuk TOPS-10 dan TOPS-20 time sharing system untuk 36-bit PDP-10 class system. Sebelum UNIX banyak digunakan, TOPS-10 adalah sistem operasi yang paling populer di universitas, dan di komunitas awal ARPANET.

Di akhir tahun 1960-an hingga akhir 1970-an, kemampuan hardware berevolusi juga software berhasil di porting agar berjalan di lebih dari satu sistem. Sistem awal banyak menggunakan microprogramming untuk mengimplementasi fitur pada sistem mereka untuk membuat arsitektur komputer menjadi tampak sama seperti yang lain dari seri komputer lainnya. Sebetulnya sebagian besar 360 sesudah 360/40 (kecuali 360/165 dan 360/168) sebetulnya menggunakan implementasi microprogram. implementations. Selanjutnya dipahami kompatibilitas aplikasi terbukti lebih penting.

Banyak sekali investasi software untuk sistem ini dilakukan sejak tahun 1960-an karena kebanyakan pembuat komputer akan mengembangkan sistem operasi yang cocok untuk hardwarenya. Beberapa sistem operasi yang mendukung mainframe adalah:

• Burroughs MCP – B5000, 1961 hingga Unisys Clearpath/MCP, sekarang.
• IBM OS/360 – IBM System/360, 1966 hingga IBM z/OS, sekarang.
• IBM CP-67 – IBM System/360, 1967 hingga IBM z/VM, sekarang.
• UNIVAC EXEC 8 – UNIVAC 1108, 1967, hingga OS 2200 Unisys Clearpath Dorado, sekarang.

Microcomputer

PC-DOS adalah awal sistem operasi untuk personal komputer yang berupa command line interface (CLI). Mac OS dari Apple Computer menjadi sistem operasi pertama yang menggunakan Graphical User Interface (GUI). Banyak dari fitur-nya seperti Windows dan Icon dikemudian hari menjadi ciri GUI.

Mikrokomputer pertama tidak mempunyai kapasitas atau kebutuhan untuk menjalankan sistem operasi yang rumit yang dikembangkan di mainframe atau mini. Sistem operasi minimalistik di kembangkan, kadang kali dimasukan kedalam ROM yang dikenal sebagai monitor. Salah satu sistem operasi awal yang cukup menonjol adalah CP/M, yang di dukung oleh banyak mikrokomputer awal dan sangat mirip dengan Microsoft MS-DOS, yang menjadi sangat populer karena dipilih sebagai sistem operasi IBM PC (versi IBM dari MS-DOS dari dikenal sebagai IBM DOS atau PC DOS). Di tahun 1980-an, Apple Computer Inc. (sekarang Apple Inc.) meninggalkan seri Apple II yang popular untuk memperkenalkan Apple Macintosh computer dengan innovative Graphical User Interface (GUI) dengan Mac OS.

Dengan di perkenalkannya CPU Intel 80386 dengan arsitektur 32-bit dan kemampuan paging, komputer personal mempunyai kemampuan untuk menjalankan sistem operasi multitasking seperti minikomputer dan mainframe yang awal. Microsoft meresponds dengan mengambil Dave Cutler, yang mengembangkan sistem operasi VMS di Digital Equipment Corporation. Dave memimpin pengembangkan sistem operasi Windows NT yang menjadi dasar dari sistem operasi Microsoft. Steve Jobs, salah satu pendiri Apple Inc., memulai NeXT Computer Inc., yang mengembangkan sistem operasi NEXTSTEP. NEXTSTEP dikemudian hari di beli oleh Apple Inc. dan digunakan, bersama dengan code dari FreeBSD sebagai inti dari Mac OS X.

GNU Project di awali oleh seorang was activis dan programmer Richard Stallman dengan tujuan untuk membuat software yang benar-benar free (bebas) sebagai pengganti dari sistem operasi UNIX yang berhak cipta (proprietary). GNU Project secara umum sangat sukses untuk menduplikasi fungsi berbagai hal dari UNIX, tapi mengembangkan sistem operasi GNU Hurd kernel tampaknya kurang produktif. Tahun 1991, seorang mahasiswa komputer science dari finland Linus Torvalds, dengan di bantu oleh banyak relawan berkolaborasi melalui Internet, melepaskan versi pertama kernel Linux. Tak lama kemudian, merger dengan komponen GNU untuk membentuk sebuah sistem operasi yang komplit. Sejak itu, kedua komponen tersebut biasanya di kenal sebagai "Linux" oleh industri software, nama yang sangat di tentang oleh Stallman maupun Free Software Foundation, mereka lebih suka dengan nama GNU/Linux. Berkeley Software Distribution, dikenal sebagai BSD, adalah turunan UNIX yang disebarkan oleh University of California, Berkeley, dimulai sekitar tahun 1970-an. BSD di sebarkan dengan bebbas dan di porting ke banyak minikomputer. BSD akhirnya memperoleh beberapa pengikut di PC, seperti, FreeBSD, NetBSD dan OpenBSD.

Contoh Sistem Operasi

Sistem Operasi UNIX dan UNIX-like

Unix awalnya ditulis menggunakan bahasa assembler. Ken Thompson menulis bahasa B, berbasis pada BCPL, berdasarkan pengalamannya di projek MULTICS. Bahasa B kemudian di ganti oleh bahasa C, dan Unix, ditulis ulang dalam bahasa C, dikembangkan menjadi keluarga sistem operasi yang besar, kompleks dan saling berhubungan yang menjadi sangat berpengaruh pada semua sistem operasi modern.

Keluarga UNIX-like adalah sebuah kelompok sistem operasi yang sangat besar, dengan beberapa sub-kategori utama, termasuk, System V, BSD, dan Linux. Nama "UNIX" adalah merek dagang dari The Open Group yang me-lisensi-kan untuk digunakan di semua sistem operasi yang sesuai dengan definisi mereka. Nama "UNIX-like" lebih sering digunakan untuk menyebutkan sistem operasi yang mirip dengan UNIX yang orisinil.

Sistem Unix-like berjalan di berbagai arsitektur komputer. Mereka banyak digunakan di server untuk usaha / bisnis, juga di workstation untuk lingkungan akademik dan engineering. Varian UNIX yang free, seperti Linux dan BSD, sangat populer di wilayah ini.

Ada empat (4) sistem operasi yang di sertifikasi oleh The Open Group (pemegang merek dagang UNIX) sebagai Unix. Sistem Operasi tersebut adalah HP-UX dan IBM AIX keduanya adalah turunan dari System V original dan hanya dapat di jalankan di hardware masing-masing vendir tersebut. Sedangkan, Sistem Operasi Solaris dari Sun Microsystem dapat dijalankan di berbagai hardware, termasuk x86 dan Sparc server, dan PC. Apple OS X,

In contrast, Sun Microsystems's Solaris Operating System can run on multiple types of hardware, including x86 and Sparc servers, and PCs. Apple's OS X, a replacement for Apple's earlier (non-Unix) Mac OS, is a hybrid kernel-based BSD variant derived from NeXTSTEP, Mach, and FreeBSD.

Unix interoperability was sought by establishing the POSIX standard. The POSIX standard can be applied to any operating system, although it was originally created for various Unix variants. BSD and its descendants

The first server for the World Wide Web ran on NeXTSTEP, based on BSD. Main article: Berkeley Software Distribution

A subgroup of the Unix family is the Berkeley Software Distribution family, which includes FreeBSD, NetBSD, and OpenBSD. These operating systems are most commonly found on webservers, although they can also function as a personal computer OS. The Internet owes much of its existence to BSD, as many of the protocols now commonly used by computers to connect, send and receive data over a network were widely implemented and refined in BSD. The world wide web was also first demonstrated on a number of computers running an OS based on BSD called NextStep.

BSD has its roots in Unix. In 1974, University of California, Berkeley installed its first Unix system. Over time, students and staff in the computer science department there began adding new programs to make things easier, such as text editors. When Berkely received new VAX computers in 1978 with Unix installed, the school's undergraduates modified Unix even more in order to take advantage of the computer's hardware possibilities. The Defense Advanced Research Projects Agency of the US Department of Defense took interest, and decided to fund the project. Many schools, corporations, and government organizations took notice and started to use Berkeley's version of Unix instead of the official one distributed by AT&T.

Steve Jobs, upon leaving Apple Inc. in 1985, formed NeXT Inc., a company that manufactured high-end computers running on a variation of BSD called NeXTSTEP. One of these computers was used by Tim Berners-Lee as the first webserver to create the World Wide Web.

Developers like Keith Bostic encouraged the project to replace any non-free code that originated with Bell Labs. Once this was done, however, AT&T sued. Eventually, after two years of legal disputes, the BSD project came out ahead and spawned a number of free derivatives, such as FreeBSD and NetBSD.

OS X

Main article: OS X The standard user interface of OS X

OS X (formerly "Mac OS X") is a line of open core graphical operating systems developed, marketed, and sold by Apple Inc., the latest of which is pre-loaded on all currently shipping Macintosh computers. OS X is the successor to the original Mac OS, which had been Apple's primary operating system since 1984. Unlike its predecessor, OS X is a UNIX operating system built on technology that had been developed at NeXT through the second half of the 1980s and up until Apple purchased the company in early 1997. The operating system was first released in 1999 as Mac OS X Server 1.0, with a desktop-oriented version (Mac OS X v10.0 "Cheetah") following in March 2001. Since then, six more distinct "client" and "server" editions of OS X have been released, the most recent being OS X 10.8 "Mountain Lion", which was first made available on February 16, 2012 for developers, and was then released to the public on July 25, 2012. Releases of OS X are named after big cats.

Prior to its merging with OS X, the server edition - OS X Server - was architecturally identical to its desktop counterpart and usually ran on Apple's line of Macintosh server hardware. OS X Server included work group management and administration software tools that provide simplified access to key network services, including a mail transfer agent, a Samba server, an LDAP server, a domain name server, and others. With Mac OS X v10.7 Lion, all server aspects of Mac OS X Server have been integrated into the client version and the product re-branded as "OS X" (dropping "Mac" from the name). The server tools are now offered as an application.[6]

Linux and GNU

Main articles: GNU, Linux, and Linux kernel Ubuntu, desktop Linux distribution Android, a popular mobile operating system using the Linux kernel

Linux (or GNU/Linux) is a Unix-like operating system that was developed without any actual Unix code, unlike BSD and its variants. Linux can be used on a wide range of devices from supercomputers to wristwatches. The Linux kernel is released under an open source license, so anyone can read and modify its code. It has been modified to run on a large variety of electronics. Although estimates suggest that Linux is used on 1.82% of all personal computers,[7][8] it has been widely adopted for use in servers[9] and embedded systems[10] (such as cell phones). Linux has superseded Unix in most places[which?], and is used on the 10 most powerful supercomputers in the world.[11] The Linux kernel is used in some popular distributions, such as Red Hat, Debian, Ubuntu, Linux Mint and Google's Android.

The GNU project is a mass collaboration of programmers who seek to create a completely free and open operating system that was similar to Unix but with completely original code. It was started in 1983 by Richard Stallman, and is responsible for many of the parts of most Linux variants. Thousands of pieces of software for virtually every operating system are licensed under the GNU General Public License. Meanwhile, the Linux kernel began as a side project of Linus Torvalds, a university student from Finland. In 1991, Torvalds began work on it, and posted information about his project on a newsgroup for computer students and programmers. He received a wave of support and volunteers who ended up creating a full-fledged kernel. Programmers from GNU took notice, and members of both projects worked to integrate the finished GNU parts with the Linux kernel in order to create a full-fledged operating system.

Google Chromium OS

Main article: Google Chromium OS

Chromium is an operating system based on the Linux kernel and designed by Google. Since Chromium OS targets computer users who spend most of their time on the Internet, it is mainly a web browser with no ability to run local applications. Instead, it relies on Internet applications (or Web apps) used in the web browser to accomplish tasks such as word processing and media viewing, as well as online storage for storing most files. Microsoft Windows Main article: Microsoft Windows Bootable Windows To Go USB flash drive Microsoft Windows 7 Desktop

Microsoft Windows is a family of proprietary operating systems designed by Microsoft Corporation and primarily targeted to Intel architecture based computers, with an estimated 88.9 percent total usage share on Web connected computers.[8][12][13][14] The newest version is Windows 8 for workstations and Windows Server 2012 for servers. Windows 7 recently overtook Windows XP as most used OS.[15][16][17]

Microsoft Windows originated in 1985 as an operating environment running on top of MS-DOS, which was the standard operating system shipped on most Intel architecture personal computers at the time. In 1995, Windows 95 was released which only used MS-DOS as a bootstrap. For backwards compatibility, Win9x could run real-mode MS-DOS[18][19] and 16 bits Windows 3.x[20] drivers. Windows ME, released in 2000, was the last version in the Win9x family. Later versions have all been based on the Windows NT kernel. Current versions of Windows run on IA-32 and x86-64 microprocessors, although Windows 8 will support ARM architecture. In the past, Windows NT supported non-Intel architectures.

Server editions of Windows are widely used. In recent years, Microsoft has expended significant capital in an effort to promote the use of Windows as a server operating system. However, Windows' usage on servers is not as widespread as on personal computers, as Windows competes against Linux and BSD for server market share.[21][22]

Lainnya

There have been many operating systems that were significant in their day but are no longer so, such as AmigaOS; OS/2 from IBM and Microsoft; Mac OS, the non-Unix precursor to Apple's Mac OS X; BeOS; XTS-300; RISC OS; MorphOS and FreeMint. Some are still used in niche markets and continue to be developed as minority platforms for enthusiast communities and specialist applications. OpenVMS formerly from DEC, is still under active development by Hewlett-Packard. Yet other operating systems are used almost exclusively in academia, for operating systems education or to do research on operating system concepts. A typical example of a system that fulfills both roles is MINIX, while for example Singularity is used purely for research.

Other operating systems have failed to win significant market share, but have introduced innovations that have influenced mainstream operating systems, not least Bell Labs' Plan 9.

Components

The components of an operating system all exist in order to make the different parts of a computer work together. All user software needs to go through the operating system in order to use any of the hardware, whether it be as simple as a mouse or keyboard or as complex as an Internet component.

Kernel

A kernel connects the application software to the hardware of a computer. Main article: Kernel (computing)

With the aid of the firmware and device drivers, the kernel provides the most basic level of control over all of the computer's hardware devices. It manages memory access for programs in the RAM, it determines which programs get access to which hardware resources, it sets up or resets the CPU's operating states for optimal operation at all times, and it organizes the data for long-term non-volatile storage with file systems on such media as disks, tapes, flash memory, etc.

Program execution

Main article: Process (computing)

The operating system provides an interface between an application program and the computer hardware, so that an application program can interact with the hardware only by obeying rules and procedures programmed into the operating system. The operating system is also a set of services which simplify development and execution of application programs. Executing an application program involves the creation of a process by the operating system kernel which assigns memory space and other resources, establishes a priority for the process in multi-tasking systems, loads program binary code into memory, and initiates execution of the application program which then interacts with the user and with hardware devices.

Interrupts

Main article: Interrupt

Interrupts are central to operating systems, as they provide an efficient way for the operating system to interact with and react to its environment. The alternative — having the operating system "watch" the various sources of input for events (polling) that require action — can be found in older systems with very small stacks (50 or 60 bytes) but are unusual in modern systems with large stacks. Interrupt-based programming is directly supported by most modern CPUs. Interrupts provide a computer with a way of automatically saving local register contexts, and running specific code in response to events. Even very basic computers support hardware interrupts, and allow the programmer to specify code which may be run when that event takes place.

When an interrupt is received, the computer's hardware automatically suspends whatever program is currently running, saves its status, and runs computer code previously associated with the interrupt; this is analogous to placing a bookmark in a book in response to a phone call. In modern operating systems, interrupts are handled by the operating system's kernel. Interrupts may come from either the computer's hardware or from the running program.

When a hardware device triggers an interrupt, the operating system's kernel decides how to deal with this event, generally by running some processing code. The amount of code being run depends on the priority of the interrupt (for example: a person usually responds to a smoke detector alarm before answering the phone). The processing of hardware interrupts is a task that is usually delegated to software called device driver, which may be either part of the operating system's kernel, part of another program, or both. Device drivers may then relay information to a running program by various means.

A program may also trigger an interrupt to the operating system. If a program wishes to access hardware for example, it may interrupt the operating system's kernel, which causes control to be passed back to the kernel. The kernel will then process the request. If a program wishes additional resources (or wishes to shed resources) such as memory, it will trigger an interrupt to get the kernel's attention.

Modes

Main articles: Protected mode and Supervisor mode Privilege rings for the x86 available in protected mode. Operating systems determine which processes run in each mode.

Modern CPUs support multiple modes of operation. CPUs with this capability use at least two modes: protected mode and supervisor mode. The supervisor mode is used by the operating system's kernel for low level tasks that need unrestricted access to hardware, such as controlling how memory is written and erased, and communication with devices like graphics cards. Protected mode, in contrast, is used for almost everything else. Applications operate within protected mode, and can only use hardware by communicating with the kernel, which controls everything in supervisor mode. CPUs might have other modes similar to protected mode as well, such as the virtual modes in order to emulate older processor types, such as 16-bit processors on a 32-bit one, or 32-bit processors on a 64-bit one.

When a computer first starts up, it is automatically running in supervisor mode. The first few programs to run on the computer, being the BIOS or EFI, bootloader, and the operating system have unlimited access to hardware – and this is required because, by definition, initializing a protected environment can only be done outside of one. However, when the operating system passes control to another program, it can place the CPU into protected mode.

In protected mode, programs may have access to a more limited set of the CPU's instructions. A user program may leave protected mode only by triggering an interrupt, causing control to be passed back to the kernel. In this way the operating system can maintain exclusive control over things like access to hardware and memory.

The term "protected mode resource" generally refers to one or more CPU registers, which contain information that the running program isn't allowed to alter. Attempts to alter these resources generally causes a switch to supervisor mode, where the operating system can deal with the illegal operation the program was attempting (for example, by killing the program).

Memory management

Main article: Memory management

Among other things, a multiprogramming operating system kernel must be responsible for managing all system memory which is currently in use by programs. This ensures that a program does not interfere with memory already in use by another program. Since programs time share, each program must have independent access to memory.

Cooperative memory management, used by many early operating systems, assumes that all programs make voluntary use of the kernel's memory manager, and do not exceed their allocated memory. This system of memory management is almost never seen any more, since programs often contain bugs which can cause them to exceed their allocated memory. If a program fails, it may cause memory used by one or more other programs to be affected or overwritten. Malicious programs or viruses may purposefully alter another program's memory, or may affect the operation of the operating system itself. With cooperative memory management, it takes only one misbehaved program to crash the system.

Memory protection enables the kernel to limit a process' access to the computer's memory. Various methods of memory protection exist, including memory segmentation and paging. All methods require some level of hardware support (such as the 80286 MMU), which doesn't exist in all computers.

In both segmentation and paging, certain protected mode registers specify to the CPU what memory address it should allow a running program to access. Attempts to access other addresses will trigger an interrupt which will cause the CPU to re-enter supervisor mode, placing the kernel in charge. This is called a segmentation violation or Seg-V for short, and since it is both difficult to assign a meaningful result to such an operation, and because it is usually a sign of a misbehaving program, the kernel will generally resort to terminating the offending program, and will report the error.

Windows 3.1-Me had some level of memory protection, but programs could easily circumvent the need to use it. A general protection fault would be produced, indicating a segmentation violation had occurred; however, the system would often crash anyway.

Virtual memory

Main article: Virtual memory Further information: Page fault Many operating systems can "trick" programs into using memory scattered around the hard disk and RAM as if it is one continuous chunk of memory, called virtual memory.

The use of virtual memory addressing (such as paging or segmentation) means that the kernel can choose what memory each program may use at any given time, allowing the operating system to use the same memory locations for multiple tasks.

If a program tries to access memory that isn't in its current range of accessible memory, but nonetheless has been allocated to it, the kernel will be interrupted in the same way as it would if the program were to exceed its allocated memory. (See section on memory management.) Under UNIX this kind of interrupt is referred to as a page fault.

When the kernel detects a page fault it will generally adjust the virtual memory range of the program which triggered it, granting it access to the memory requested. This gives the kernel discretionary power over where a particular application's memory is stored, or even whether or not it has actually been allocated yet.

In modern operating systems, memory which is accessed less frequently can be temporarily stored on disk or other media to make that space available for use by other programs. This is called swapping, as an area of memory can be used by multiple programs, and what that memory area contains can be swapped or exchanged on demand.

"Virtual memory" provides the programmer or the user with the perception that there is a much larger amount of RAM in the computer than is really there.[23]

Multitasking

Main articles: Computer multitasking and Process management (computing) Further information: Context switch, Preemptive multitasking, and Cooperative multitasking

Multitasking refers to the running of multiple independent computer programs on the same computer; giving the appearance that it is performing the tasks at the same time. Since most computers can do at most one or two things at one time, this is generally done via time-sharing, which means that each program uses a share of the computer's time to execute.

An operating system kernel contains a piece of software called a scheduler which determines how much time each program will spend executing, and in which order execution control should be passed to programs. Control is passed to a process by the kernel, which allows the program access to the CPU and memory. Later, control is returned to the kernel through some mechanism, so that another program may be allowed to use the CPU. This so-called passing of control between the kernel and applications is called a context switch.

An early model which governed the allocation of time to programs was called cooperative multitasking. In this model, when control is passed to a program by the kernel, it may execute for as long as it wants before explicitly returning control to the kernel. This means that a malicious or malfunctioning program may not only prevent any other programs from using the CPU, but it can hang the entire system if it enters an infinite loop.

Modern operating systems extend the concepts of application preemption to device drivers and kernel code, so that the operating system has preemptive control over internal run-times as well.

The philosophy governing preemptive multitasking is that of ensuring that all programs are given regular time on the CPU. This implies that all programs must be limited in how much time they are allowed to spend on the CPU without being interrupted. To accomplish this, modern operating system kernels make use of a timed interrupt. A protected mode timer is set by the kernel which triggers a return to supervisor mode after the specified time has elapsed. (See above sections on Interrupts and Dual Mode Operation.)

On many single user operating systems cooperative multitasking is perfectly adequate, as home computers generally run a small number of well tested programs. The AmigaOS is an exception, having pre-emptive multitasking from its very first version. Windows NT was the first version of Microsoft Windows which enforced preemptive multitasking, but it didn't reach the home user market until Windows XP (since Windows NT was targeted at professionals).

Disk access and file systems

Main article: Virtual file system Filesystems allow users and programs to organize and sort files on a computer, often through the use of directories (or "folders")

Access to data stored on disks is a central feature of all operating systems. Computers store data on disks using files, which are structured in specific ways in order to allow for faster access, higher reliability, and to make better use out of the drive's available space. The specific way in which files are stored on a disk is called a file system, and enables files to have names and attributes. It also allows them to be stored in a hierarchy of directories or folders arranged in a directory tree.

Early operating systems generally supported a single type of disk drive and only one kind of file system. Early file systems were limited in their capacity, speed, and in the kinds of file names and directory structures they could use. These limitations often reflected limitations in the operating systems they were designed for, making it very difficult for an operating system to support more than one file system.

While many simpler operating systems support a limited range of options for accessing storage systems, operating systems like UNIX and Linux support a technology known as a virtual file system or VFS. An operating system such as UNIX supports a wide array of storage devices, regardless of their design or file systems, allowing them to be accessed through a common application programming interface (API). This makes it unnecessary for programs to have any knowledge about the device they are accessing. A VFS allows the operating system to provide programs with access to an unlimited number of devices with an infinite variety of file systems installed on them, through the use of specific device drivers and file system drivers.

A connected storage device, such as a hard drive, is accessed through a device driver. The device driver understands the specific language of the drive and is able to translate that language into a standard language used by the operating system to access all disk drives. On UNIX, this is the language of block devices.

When the kernel has an appropriate device driver in place, it can then access the contents of the disk drive in raw format, which may contain one or more file systems. A file system driver is used to translate the commands used to access each specific file system into a standard set of commands that the operating system can use to talk to all file systems. Programs can then deal with these file systems on the basis of filenames, and directories/folders, contained within a hierarchical structure. They can create, delete, open, and close files, as well as gather various information about them, including access permissions, size, free space, and creation and modification dates.

Various differences between file systems make supporting all file systems difficult. Allowed characters in file names, case sensitivity, and the presence of various kinds of file attributes makes the implementation of a single interface for every file system a daunting task. Operating systems tend to recommend using (and so support natively) file systems specifically designed for them; for example, NTFS in Windows and ext3 and ReiserFS in Linux. However, in practice, third party drives are usually available to give support for the most widely used file systems in most general-purpose operating systems (for example, NTFS is available in Linux through NTFS-3g, and ext2/3 and ReiserFS are available in Windows through third-party software).

Support for file systems is highly varied among modern operating systems, although there are several common file systems which almost all operating systems include support and drivers for. Operating systems vary on file system support and on the disk formats they may be installed on. Under Windows, each file system is usually limited in application to certain media; for example, CDs must use ISO 9660 or UDF, and as of Windows Vista, NTFS is the only file system which the operating system can be installed on. It is possible to install Linux onto many types of file systems. Unlike other operating systems, Linux and UNIX allow any file system to be used regardless of the media it is stored in, whether it is a hard drive, a disc (CD,DVD...), a USB flash drive, or even contained within a file located on another file system.

Device drivers

Main article: Device driver

A device driver is a specific type of computer software developed to allow interaction with hardware devices. Typically this constitutes an interface for communicating with the device, through the specific computer bus or communications subsystem that the hardware is connected to, providing commands to and/or receiving data from the device, and on the other end, the requisite interfaces to the operating system and software applications. It is a specialized hardware-dependent computer program which is also operating system specific that enables another program, typically an operating system or applications software package or computer program running under the operating system kernel, to interact transparently with a hardware device, and usually provides the requisite interrupt handling necessary for any necessary asynchronous time-dependent hardware interfacing needs.

The key design goal of device drivers is abstraction. Every model of hardware (even within the same class of device) is different. Newer models also are released by manufacturers that provide more reliable or better performance and these newer models are often controlled differently. Computers and their operating systems cannot be expected to know how to control every device, both now and in the future. To solve this problem, operating systems essentially dictate how every type of device should be controlled. The function of the device driver is then to translate these operating system mandated function calls into device specific calls. In theory a new device, which is controlled in a new manner, should function correctly if a suitable driver is available. This new driver will ensure that the device appears to operate as usual from the operating system's point of view.

Under versions of Windows before Vista and versions of Linux before 2.6, all driver execution was co-operative, meaning that if a driver entered an infinite loop it would freeze the system. More recent revisions of these operating systems incorporate kernel preemption, where the kernel interrupts the driver to give it tasks, and then separates itself from the process until it receives a response from the device driver, or gives it more tasks to do.

Networking

Main article: Computer network

Currently most operating systems support a variety of networking protocols, hardware, and applications for using them. This means that computers running dissimilar operating systems can participate in a common network for sharing resources such as computing, files, printers, and scanners using either wired or wireless connections. Networks can essentially allow a computer's operating system to access the resources of a remote computer to support the same functions as it could if those resources were connected directly to the local computer. This includes everything from simple communication, to using networked file systems or even sharing another computer's graphics or sound hardware. Some network services allow the resources of a computer to be accessed transparently, such as SSH which allows networked users direct access to a computer's command line interface.

Client/server networking allows a program on a computer, called a client, to connect via a network to another computer, called a server. Servers offer (or host) various services to other network computers and users. These services are usually provided through ports or numbered access points beyond the server's network address. Each port number is usually associated with a maximum of one running program, which is responsible for handling requests to that port. A daemon, being a user program, can in turn access the local hardware resources of that computer by passing requests to the operating system kernel.

Many operating systems support one or more vendor-specific or open networking protocols as well, for example, SNA on IBM systems, DECnet on systems from Digital Equipment Corporation, and Microsoft-specific protocols (SMB) on Windows. Specific protocols for specific tasks may also be supported such as NFS for file access. Protocols like ESound, or esd can be easily extended over the network to provide sound from local applications, on a remote system's sound hardware.

Security

Main article: Computer security

A computer being secure depends on a number of technologies working properly. A modern operating system provides access to a number of resources, which are available to software running on the system, and to external devices like networks via the kernel.

The operating system must be capable of distinguishing between requests which should be allowed to be processed, and others which should not be processed. While some systems may simply distinguish between "privileged" and "non-privileged", systems commonly have a form of requester identity, such as a user name. To establish identity there may be a process of authentication. Often a username must be quoted, and each username may have a password. Other methods of authentication, such as magnetic cards or biometric data, might be used instead. In some cases, especially connections from the network, resources may be accessed with no authentication at all (such as reading files over a network share). Also covered by the concept of requester identity is authorization; the particular services and resources accessible by the requester once logged into a system are tied to either the requester's user account or to the variously configured groups of users to which the requester belongs.

In addition to the allow/disallow model of security, a system with a high level of security will also offer auditing options. These would allow tracking of requests for access to resources (such as, "who has been reading this file?"). Internal security, or security from an already running program is only possible if all possibly harmful requests must be carried out through interrupts to the operating system kernel. If programs can directly access hardware and resources, they cannot be secured.

External security involves a request from outside the computer, such as a login at a connected console or some kind of network connection. External requests are often passed through device drivers to the operating system's kernel, where they can be passed onto applications, or carried out directly. Security of operating systems has long been a concern because of highly sensitive data held on computers, both of a commercial and military nature. The United States Government Department of Defense (DoD) created the Trusted Computer System Evaluation Criteria (TCSEC) which is a standard that sets basic requirements for assessing the effectiveness of security. This became of vital importance to operating system makers, because the TCSEC was used to evaluate, classify and select trusted operating systems being considered for the processing, storage and retrieval of sensitive or classified information.

Network services include offerings such as file sharing, print services, email, web sites, and file transfer protocols (FTP), most of which can have compromised security. At the front line of security are hardware devices known as firewalls or intrusion detection/prevention systems. At the operating system level, there are a number of software firewalls available, as well as intrusion detection/prevention systems. Most modern operating systems include a software firewall, which is enabled by default. A software firewall can be configured to allow or deny network traffic to or from a service or application running on the operating system. Therefore, one can install and be running an insecure service, such as Telnet or FTP, and not have to be threatened by a security breach because the firewall would deny all traffic trying to connect to the service on that port.

An alternative strategy, and the only sandbox strategy available in systems that do not meet the Popek and Goldberg virtualization requirements, is the operating system not running user programs as native code, but instead either emulates a processor or provides a host for a p-code based system such as Java.

Internal security is especially relevant for multi-user systems; it allows each user of the system to have private files that the other users cannot tamper with or read. Internal security is also vital if auditing is to be of any use, since a program can potentially bypass the operating system, inclusive of bypassing auditing.

User interface

A screenshot of the Bourne Again Shell command line. Each command is typed out after the 'prompt', and then its output appears below, working its way down the screen. The current command prompt is at the bottom. Main article: Operating system user interface

Every computer that is to be operated by an individual requires a user interface. The user interface is usually referred to as a shell and is essential if human interaction is to be supported. The user interface views the directory structure and requests services from the operating system that will acquire data from input hardware devices, such as a keyboard, mouse or credit card reader, and requests operating system services to display prompts, status messages and such on output hardware devices, such as a video monitor or printer. The two most common forms of a user interface have historically been the command-line interface, where computer commands are typed out line-by-line, and the graphical user interface, where a visual environment (most commonly a WIMP) is present. Graphical user interfaces A screenshot of the KDE Plasma Desktop graphical user interface. Programs take the form of images on the screen, and the files, folders (directories), and applications take the form of icons and symbols. A mouse is used to navigate the computer.

Most of the modern computer systems support graphical user interfaces (GUI), and often include them. In some computer systems, such as the original implementation of Mac OS, the GUI is integrated into the kernel.

While technically a graphical user interface is not an operating system service, incorporating support for one into the operating system kernel can allow the GUI to be more responsive by reducing the number of context switches required for the GUI to perform its output functions. Other operating systems are modular, separating the graphics subsystem from the kernel and the Operating System. In the 1980s UNIX, VMS and many others had operating systems that were built this way. Linux and Mac OS X are also built this way. Modern releases of Microsoft Windows such as Windows Vista implement a graphics subsystem that is mostly in user-space; however the graphics drawing routines of versions between Windows NT 4.0 and Windows Server 2003 exist mostly in kernel space. Windows 9x had very little distinction between the interface and the kernel.

Many computer operating systems allow the user to install or create any user interface they desire. The X Window System in conjunction with GNOME or KDE Plasma Desktop is a commonly found setup on most Unix and Unix-like (BSD, Linux, Solaris) systems. A number of Windows shell replacements have been released for Microsoft Windows, which offer alternatives to the included Windows shell, but the shell itself cannot be separated from Windows.

Numerous Unix-based GUIs have existed over time, most derived from X11. Competition among the various vendors of Unix (HP, IBM, Sun) led to much fragmentation, though an effort to standardize in the 1990s to COSE and CDE failed for various reasons, and were eventually eclipsed by the widespread adoption of GNOME and K Desktop Environment. Prior to free software-based toolkits and desktop environments, Motif was the prevalent toolkit/desktop combination (and was the basis upon which CDE was developed).

Graphical user interfaces evolve over time. For example, Windows has modified its user interface almost every time a new major version of Windows is released, and the Mac OS GUI changed dramatically with the introduction of Mac OS X in 1999.[24]

Real-time operating systems

Main article: Real-time operating system

A real-time operating system (RTOS) is a multitasking operating system intended for applications with fixed deadlines (real-time computing). Such applications include some small embedded systems, automobile engine controllers, industrial robots, spacecraft, industrial control, and some large-scale computing systems.

An early example of a large-scale real-time operating system was Transaction Processing Facility developed by American Airlines and IBM for the Sabre Airline Reservations System.

Embedded systems that have fixed deadlines use a real-time operating system such as VxWorks, PikeOS, eCos, QNX, MontaVista Linux and RTLinux. Windows CE is a real-time operating system that shares similar APIs to desktop Windows but shares none of desktop Windows' codebase.[citation needed] Symbian OS also has an RTOS kernel (EKA2) starting with version 8.0b.

Some embedded systems use operating systems such as Palm OS, BSD, and Linux, although such operating systems do not support real-time computing.

Operating system development as a hobby

See also: Hobbyist operating system development

Operating system development is one of the most complicated activities in which a computing hobbyist may engage. A hobby operating system may be classified as one whose code has not been directly derived from an existing operating system, and has few users and active developers. [25]

In some cases, hobby development is in support of a "homebrew" computing device, for example, a simple single-board computer powered by a 6502 microprocessor. Or, development may be for an architecture already in widespread use. Operating system development may come from entirely new concepts, or may commence by modeling an existing operating system. In either case, the hobbyist is his/her own developer, or may interact with a small and sometimes unstructured group of individuals who have like interests.

Examples of a hobby operating system include ReactOS and Syllable. Diversity of operating systems and portability

Application software is generally written for use on a specific operating system, and sometimes even for specific hardware. When porting the application to run on another OS, the functionality required by that application may be implemented differently by that OS (the names of functions, meaning of arguments, etc.) requiring the application to be adapted, changed, or otherwise maintained.

This cost in supporting operating systems diversity can be avoided by instead writing applications against software platforms like Java or Qt. These abstractions have already borne the cost of adaptation to specific operating systems and their system libraries.

Another approach is for operating system vendors to adopt standards. For example, POSIX and OS abstraction layers provide commonalities that reduce porting costs.

Referensi

• http://en.wikipedia.org/wiki/Operating_system
• http://www.mui.or.id/konten/fatwa-mui/fatwa-tentang-hak-kekayaan-intelektual - Haram Membajak Software!

Pranala Menarik

• Linux
• Ubuntu