Parallel Computation

Quantum Computation

Cloud Computing

What is cloud computing?

Cloud computing means that instead of all the computer hardware and software you're using sitting on your desktop, or somewhere inside your company's network, it's provided for you as a service by another company and accessed over the Internet, usually in a completely seamless way. Exactly where the hardware and software is located and how it all works doesn't matter to you, the user—it's just somewhere up in the nebulous "cloud" that the Internet represents.

Cloud computing is a buzzword that means different things to different people. For some, it's just another way of describing IT (information technology) "outsourcing"; others use it to mean any computing service provided over the Internet or a similar network; and some define it as any bought-in computer service you use that sits outside your firewall. However we define cloud computing, there's no doubt it makes most sense when we stop talking about abstract definitions and look at some simple, real examples—so let's do just that.

Simple examples of cloud computing

Most of us use cloud computing all day long without realizing it. When you sit at your PC and type a query into Google, the computer on your desk isn't playing much part in finding the answers you need: it's no more than a messenger. The words you type are swiftly shuttled over the Net to one of Google's hundreds of thousands of clustered PCs, which dig out your results and send them promptly back to you. When you do a Google search, the real work in finding your answers might be done by a computer sitting in California, Dublin, Tokyo, or Beijing; you don't know—and most likely you don't care!

The same applies to Web-based email. Once upon a time, email was something you could only send and receive using a program running on your PC (sometimes called a mail client). But then Web-based services such as Hotmail came along and carried email off into the cloud. Now we're all used to the idea that emails can be stored and processed through a server in some remote part of the world, easily accessible from a Web browser, wherever we happen to be. Pushing email off into the cloud makes it supremely convenient for busy people, constantly on the move.

Preparing documents over the Net is a newer example of cloud computing. Simply log on to a web-based service such as Google Documents and you can create a document, spreadsheet, presentation, or whatever you like using Web-based software. Instead of typing your words into a program like Microsoft Word or OpenOffice, running on your computer, you're using similar software running on a PC at one of Google's world-wide data centers. Like an email drafted on Hotmail, the document you produce is stored remotely, on a Web server, so you can access it from any Internet-connected computer, anywhere in the world, any time you like. Do you know where it's stored? No! Do you care where it's stored? Again, no! Using a Web-based service like this means you're "contracting out" or "outsourcing" some of your computing needs to a company such as Google: they pay the cost of developing the software and keeping it up-to-date and they earn back the money to do this through advertising and other paid-for services.

What makes cloud computing different?

It's managed

Most importantly, the service you use is provided by someone else and managed on your behalf. If you're using Google Documents, you don't have to worry about buying umpteen licenses for word-processing software or keeping them up-to-date. Nor do you have to worry about viruses that might affect your computer or about backing up the files you create. Google does all that for you. One basic principle of cloud computing is that you no longer need to worry how the service you're buying is provided: with Web-based services, you simply concentrate on whatever your job is and leave the problem of providing dependable computing to someone else.

It's "on-demand"

Cloud services are available on-demand and often bought on a "pay-as-you go" or subscription basis. So you typically buy cloud computing the same way you'd buy electricity, telephone services, or Internet access from a utility company. Sometimes cloud computing is free or paid-for in other ways (Hotmail is subsidized by advertising, for example). Just like electricity, you can buy as much or as little of a cloud computing service as you need from one day to the next. That's great if your needs vary unpredictably: it means you don't have to buy your own gigantic computer system and risk have it sitting there doing nothing.

It's public or private

Now we all have PCs on our desks, we're used to having complete control over our computer systems—and complete responsibility for them as well. Cloud computing changes all that. It comes in two basic flavors, public and private, which are the cloud equivalents of the Internet and Intranets. Web-based email and free services like the ones Google provides are the most familiar examples of public clouds. The world's biggest online retailer, Amazon, became the world's largest provider of public cloud computing in early 2006. When it found it was using only a fraction of its huge, global, computing power, it started renting out its spare capacity over the Net through a new entity called Amazon Web Services. Private cloud computing works in much the same way but you access the resources you use through secure network connections, much like an Intranet. Companies such as Amazon also let you use their publicly accessible cloud to make your own secure private cloud, known as a Virtual Private Cloud (VPC), using virtual private network (VPN) connections.

Types of cloud computing

IT people talk about three different kinds of cloud computing, where different services are being provided for you. Note that there's a certain amount of vagueness about how these things are defined and some overlap between them.

• Infrastructure as a Service (IaaS) means you're buying access to raw computing hardware over the Net, such as servers or storage. Since you buy what you need and pay-as-you-go, this is often referred to as utility computing. Ordinary web hosting is a simple example of IaaS: you pay a monthly subscription or a per-megabyte/gigabyte fee to have a hosting company serve up files for your website from their servers.
• Software as a Service (SaaS) means you use a complete application running on someone else's system. Web-based email and Google Documents are perhaps the best-known examples. Zoho is another well-known SaaS provider offering a variety of office applications online.
• Platform as a Service (PaaS) means you develop applications using Web-based tools so they run on systems software and hardware provided by another company. So, for example, you might develop your own ecommerce website but have the whole thing, including the shopping cart, checkout, and payment mechanism running on a merchant's server. Force.com (from salesforce.com) and the Google App Engine are examples of PaaS.

Advantages and disadvantages of cloud computing

What's good and bad about cloud computing?

Advantages

The pros of cloud computing are obvious and compelling. If your business is selling books or repairing shoes, why get involved in the nitty gritty of buying and maintaining a complex computer system? If you run an insurance office, do you really want your sales agents wasting time running anti-virus software, upgrading word-processors, or worrying about hard-drive crashes? Do you really want them cluttering your expensive computers with their personal emails, illegally shared MP3 files, and naughty YouTube videos—when you could leave that responsibility to someone else? Cloud computing allows you to buy in only the services you want, when you want them, cutting the upfront capital costs of computers and peripherals. You avoid equipment going out of date and other familiar IT problems like ensuring system security and reliability. You can add extra services (or take them away) at a moment's notice as your business needs change. It's really quick and easy to add new applications or services to your business without waiting weeks or months for the new computer (and its software) to arrive.

Drawbacks

Instant convenience comes at a price. Instead of purchasing computers and software, cloud computing means you buy services, so one-off, upfront capital costs become ongoing operating costs instead. That might work out much more expensive in the long-term.

If you're using software as a service (for example, writing a report using an online word processor or sending emails through webmail), you need a reliable, high-speed, broadband Internet connection functioning the whole time you're working. That's something we take for granted in countries such as the United States, but it's much more of an issue in developing countries or rural areas where broadband is unavailable.

If you're buying in services, you can buy only what people are providing, so you may be restricted to off-the-peg solutions rather than ones that precisely meet your needs. Not only that, but you're completely at the mercy of your suppliers if they suddenly decide to stop supporting a product you've come to depend on. (Google, for example, upset many users when it announced in September 2012 that its cloud-based Google Docs would drop support for old but de facto standard Microsoft Office file formats such as .DOC, .XLS, and .PPT, giving a mere one week's notice of the change—although, after public pressure, it later extended the deadline by three months.) Critics charge that cloud-computing is a return to the bad-old days of mainframes and proprietary systems, where businesses are locked into unsuitable, long-term arrangements with big, inflexible companies. Instead of using "generative" systems (ones that can be added to and extended in exciting ways the developers never envisaged), you're effectively using "dumb terminals" whose uses are severely limited by the supplier. Good for convenience and security, perhaps, but what will you lose in flexibility? And is such a restrained approach good for the future of the Internet as a whole? (To see why it may not be, take a look at Jonathan Zittrain's eloquent book The Future of the Internet—And How to Stop It.)

Types of Distributed Systems

The conclution of Mobile Computing Effects to Education Computing Progress.

The conclution of Mobile Computing Effects to Education Computing Progress.

In the mobile computing digital era has many roles in improving the quality in world of education. Because it could help and facilitate the day-to-day learning. The capabilities and characteristics of mobile computing also allows the distance learning process to be more effective and efficient and get better result. Even according to M. Mukhopadhay M., 1992 “Globalization has triggered a shift in education from to-face education conventional to more open education.

Many developed countries already implementing mobile computing technology in teaching and learning process. For example, mobile computing in developed countries is learning together in their education, or called collaborative learning, has been proven to improve test score and reduce dropouts by 22%. Mobile technology has found a way to be able to perform collaborative learning, in wich various students can discuss in the web forum to make database together, about anything based their location each other. In France, the project “Flexible Learning” has been applied to the system of education. It is reminiscent of Ivan Illich forecast early 70s on “Education without school (Deschooling Socieiy)”. Meanwhile in developing countries like Malaysia, “Problem Based Learning” with mobile learning technology or M-Learning is said still new in terms of its implementation. For Harvard Medical School project, ArcStream Solutions was hired to develop solutions based on the Palm OS mobile platform that facilitates communication between students and faculty, and which provide detailed program information. Florida State University College of Medicine is used to develop a solution ArcStream Clinical Data Collection System ( CDC ) which allows students to take and edit patient reports . But development continued in order to obtain good results for the quality of education in Indonesia .

The advantages of mobile computing:

• ·         The use of e-books to be efficient in the learning process.
• ·         Being less expensive because of the lack of accommodation for buildings, school supplies, and    transportation.
• ·         Academic students can be controlled by the parents.

Disadvantages of mobile computing:

• ·         The storage capacity of mobile computing technology becomes a problem
• ·         Depending on the sophistication of the Internet and mobile devices
• ·         In terms of psychology, socialization or interaction of neighbor will be reduced this will result in people tend to be apathetic.

Proses Thread

Thread

Thread adalah sebuah alur kontrol dari sebuah proses. Kontrol thread tunggal ini hanya memungkinkan proses untuk menjalankan satu tugas pada satu waktu. Banyak sistem operasi modern telah memiliki konsep yang dikembangkan agar memungkinkan sebuah proses untuk memiliki eksekusi multi-threads, agar dapat secara terus menerus mengetik dan menjalankan pemeriksaan ejaan didalam proses yang sama, maka sistem operasi tersebut memungkinkan proses untuk menjalankan lebih dari satu tugas pada satu waktu. Suatu proses yang multithreaded mengandung beberapa perbedaan alur kontrol dengan ruang alamat yang sama.

Keuntungan dari multithreaded meliputi peningkatan respon dari pengguna, pembagian sumber daya proses, ekonomis, dan kemampuan untuk mengambil keuntungan dari arsitektur multiprosesor. Thread merupakan unit dasar dari penggunaan CPU, yang terdiri dari Thread_ID, program counter, register set, dan stack. Sebuah thread berbagi code section, data section, dan sumber daya sistem operasi dengan Thread lain yang dimiliki oleh proses yang sama. Thread juga sering disebut lightweight process. Sebuah proses tradisional atau heavyweight process mempunyai thread tunggal yang berfungsi sebagai pengendali.

Perbedaan antara proses dengan thread tunggal dan proses dengan thread yang banyak adalah proses dengan thread banyak dapat mengerjakan lebih dari satu tugas pada satu satuan waktu.

Gambar 3.1. Thread

Banyak perangkat lunak yang berjalan pada PC modern dirancang secara multi-threading. Sebuah aplikasi biasanya diimplementasi sebagai proses yang terpisah dengan beberapa thread yang berfungsi sebagai pengendali. Contohnya sebuah web browser mempunyai thread untuk menampilkan gambar atau tulisan sedangkan thread yang lain berfungsi sebagai penerima data dari network.

Kadang kala ada situasi dimana sebuah aplikasi diperlukan untuk menjalankan beberapa tugas yang serupa. Sebagai contohnya sebuah web server dapat mempunyai ratusan klien yang mengaksesnya secara concurrent. Kalau web server berjalan sebagai proses yang hanya mempunyai thread tunggal maka ia hanya dapat melayani

Proses Hal. 1 Sistem Terdistribusi

satu klien pada pada satu satuan waktu. Bila ada klien lain yang ingin mengajukan permintaan maka ia harus menunggu sampai klien sebelumnya selesai dilayani. Solusinya adalah dengan membuat web server menjadi multi-threading. Dengan ini maka sebuah web server akan membuat thread yang akan mendengar permintaan klien, ketika permintaan lain diajukan maka web server akan menciptakan thread lain yang akan melayani permintaan tersebut.

Keuntungan Thread

Keuntungan dari program yang multithreading dapat dipisah menjadi empat kategori:

1. Responsi: Membuat aplikasi yang interaktif menjadi multithreading dapat membuat sebuah program terus berjalan meski pun sebagian dari program tersebut diblok atau melakukan operasi yang panjang, karena itu dapat meningkatkan respons kepada pengguna. Sebagai contohnya dalam web browser yang multithreading, sebuah thread dapat melayani permintaan pengguna sementara thread lain berusaha menampilkan image.

2. Berbagi sumber daya: thread berbagi memori dan sumber daya dengan thread lain yang dimiliki oleh proses yang sama. Keuntungan dari berbagi kode adalah mengizinkan sebuah aplikasi untuk mempunyai beberapa thread yang berbeda dalam lokasi memori yang sama.

3. Ekonomi: dalam pembuatan sebuah proses banyak dibutuhkan pengalokasian memori dan sumber daya. Alternatifnya adalah dengan penggunaan thread, karena thread berbagi memori dan sumber daya proses yang memilikinya maka akan lebih ekonomis untuk membuat dan context switch thread. Akan susah untuk mengukur perbedaan waktu antara proses dan thread dalam hal pembuatan dan pengaturan, tetapi secara umum pembuatan dan pengaturan proses lebih lama dibandingkan thread. Pada Solaris, pembuatan proses lebih lama 30 kali dibandingkan pembuatan thread, dan context switch proses 5 kali lebih lama dibandingkan context switch thread.

     4. Utilisasi arsitektur multiprocessor: Keuntungan dari multithreading dapat sangat meningkat pada   arsitektur multiprocessor, dimana setiap thread dapat berjalan secara pararel di atas processor yang berbeda. Pada arsitektur processor tunggal, CPU menjalankan setiap thread secara bergantian tetapi hal ini berlangsung sangat cepat sehingga menciptakan ilusi pararel, tetapi pada kenyataannya hanya satu thread yang dijalankan CPU pada satu-satuan waktu (satu-satuan waktu pada CPU biasa disebut time slice atau quantum). 


source:
http://naeli.staff.gunadarma.ac.id/Downloads/folder/0.1
http://www.itinfopoint.com/contentsimages/20130603-multithread.png
http://dee-x-cisadane.webs.com/apps/blog/show/10299581-perbedaan-proses-dan-thread-perbedaan-file-service-file-system-dan-file-server-beserta-contohnya-

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Remote Procedure Call

Definisi RPC

RPC adalah suatu protokol yang menyediakan suatu mekanisme

komunikasi antar proses yang mengijinkan suatu program untuk berjalan

pada suatu komputer tanpa terasa adanya eksekusi kode pada sistem yang

jauh (remote system). RPC mengasumsi keberadaan dari low-level protokol

transportasi seperti TCP atau UDP untuk membawa pesan data dalam

komunikasi suatu program. Protokol RPC dibangun diatas protokol eXternal

Data Representation (XDR), yang merupakan standar dari representasi data

dalam komunikasi remote. Protokol XDR mengubah parameter dan hasil dari

tiap servis RPC yang disediakan.

Protokol RPC mengijinkan pengguna (users) untuk bekerja dengan

prosedur remote sebagaimana bekerja dengan prosedur lokal. Prosedur

panggilan remote (remote procedure calls) didefinisikan melalui rutin yang

terkandung didalam protokol RPC. Tiap message dari panggilan akan

disesuaikan dengan message balikan. Protokol RPC sendiri sebenarnya adalah

suatu protokol untuk ”meneruskan pesan” yang mengimplemntasikan

protokol non-RPC lain seperti panggilan remote batching dan broadcasting.

Protokol ini juga mendukung adanya prosedur callback dan select subroutine pada sisi server.

Kelebihan dan Kekurangan RPC
Kelebihan RPC

-Relatif mudah digunakan : Pemanggilan remote procedure tidak jauh berbeda dibandingkan pemanggilan local procedure. Sehingga pemrogram dapat berkonsentrasi pada software logic, tidak perlu memikirkan low level details seperti socket, marshalling & unmarshalling.

-Robust (Sempurna): Sejak th 1980-an RPC telah banyak digunakan dlm pengembangan mission-critical application yg memerlukan scalability, fault tolerance, & reliability.

Kekurangan RPC

- Tidak fleksibel terhadap perubahan: hubungan anatara client dan server bersifat static.

- Berdasarkan prosedural/structured programming yang sudah ketinggalan jaman dibandingkan OOP.


Prinsip Dasar RPC

Skema RPC ini dilakukan juga pada proses-proses 

Langkah-langkah dalam RPC 

1. Prosedur client memanggil client stub
2. Client stub membuat pesan dan memanggil OS client
3. OS client mengirim pesan ke OS server
4. OS server memberikan pesan ke server stub
5. Server stub meng-unpack parameter-parameter untuk memanggil server
6. Server mengerjakan operasi, dan mengembalikan hasilnya ke server stub
7. Server stub mem-pack hasil tsb dan memanggil OS server
8. OS server mengirim pesan (hasil) ke OS client
9. OS client memberikan pesan tersebut ke client stub
10. Client stub meng-unpack hasil dan mengembalikan hasil tersebut ke Clientyang running di komputer berlainan

Sebelum mekanisme RPC digunakan, data harus di-packaging ke dalam format transimisi. Langkah ini dinamakan marshalling. Proxy bertanggung jawab untuk marshalling data, kemudian mengirimkan data dan meminta instans dari komponen (remote). Stub menerima request, unmarshall data, dan memanggil method yang diminta. Kemudian proses mengembalikan nilai yang diinginkan (Stub adalah kode untuk mengkonversi parameter yang dipassing saat RPC berjalan).




source:

http://naeli.staff.gunadarma.ac.id/Downloads/files/8465/Komunikasi_revisi.pdf

http://kambing.ui.ac.id/bebas/v06/Kuliah/SistemOperasi/BUKU/SistemOperasi-4.X-1/ch17s06.html

http://en.wikipedia.org/wiki/Remote_procedure_call


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