Ernesto L Zanabria | First Project

Operating Systems Fundamentals

An Introduction to Operating Systems

A computer's functions and features can be broken down into three basic tasks all computers perform: input, processing, and output. Information is input to a computer from a device such as keyboard of from storage device such as hard drive; the central processing unit (CPU) processes the information, and then output is usually created. An operating system (OS) is a specialized computer program that provides the following features:

User interface—The user interface provides a method for users to interact with the computer, usually with a keyboard and mouse or touch screen. A user clicks, touches, or types; the computer processes the input and provides some type of output.

File system—The file system is the method by which an OS stores and organizes files and manages access to files on a storage device, such as a hard drive.

Processes and services—A process is a program that's loaded into memory and run by the CPU. It can be an application a user interacts with, such as a word-processing program or a Web browser, or a program with no user interface that communicates with and provides services to other processes. This type of process is usually called a service in Windows and a daemon in Linux, and is said to run in the background because there's no user interface.

Kernel—The Kernel is the heart of the OS and runs with the highest priority. It schedules processes to run, making sure high-priority processes are taken care of first; manages memory to ensure that two applications don't attempt to use the same memory space; and makes sure I/O devices are accessed by only one process at a time, in addition to other tasks.

The Central Processing Unit

The CPU is the chip that performs the actual computational and logic work. Most modern PCs have one such chip, and are referred to as single-processor computers. In reality, to ensure complete functionality,the CPU requires several support chips, such as chips that help manage communication with devices and device drivers. Chip technology continues to develop with the addition of multicore processors. A processor core is the part of the CPU that reads and executes basic instrucions, such as reading and writing data from and to memory or executing an arithmetic operation. CPUs were originally created to have only one core and thus perform only one instruction at a time. A multicore processor has two or more cores—for exmaple, a dual-core processor contains two cores and a quad-core processor has four. The most processor cores used in a traditional PC desktops and servers is 16 as of this writing, but high-end CPUs, such as Intel's Knights Landing, have up to 72 cores. Development continues in this area, and scientists so far have put as many as 1000 cores on a single CPU chip.

Basic CPU Architecture

Most CPUs are composed of the following elements:

Control unit—The control unit (CU) is the director of operations in the CPU. The control unit provides timing and cordination between the other parts of the CPU, such as the arithmetic logic unit, registers, and system bus. For example, when a new instruction should be executed, the control unit receives and decodes the instruction and tells the arithmetic logic unit to execute it.

Arithmetic logic unit—The arithmetic logic unit (ALU) performs the primary task of any CPU, which is to execute instructions. These might be arithmetic instructions, such as addition or multiplication of integers, or logic instructions, such as binary AND or binary OR instructions. Most CPUs also contain a floating point unit (FPU) that performs floating point operations.

Registers—A register is a temporary holding location on a CPU where data must be placed before the CPU can use it. There are instruction registers that hold the instruction the CPU executes, such as add, multiply, or store. Also, the CPU uses address registers to access data stored in RAM, and data registers that hold the data the CPU is currently working with, such as two numbers used in an add or multiply instruction.

System bus—The system bus is a series of lanes that are used to communicate between the CPU and other major parts of the computer, such as RAM and input/output (I/O) devices. There are actually three types of buses: the control bus,address bus, and data bus. The control bus carries status signal between the CPU and other devices. Status signals inform the CPU that a device needs attention; for example, when an input device has data ready, the CPU must execute the device driver code to read the data from the device. The address bus carries address signals to indicate where data should be read from or written to in the system's memory. The data bus carries actual data that is being read from or written to the system memory.

Cloud Computing Fundamentals

Cloud computing is a networking model in which data, applications, and processing power are managed by servers on the Internet; users of these resources pay for what they use rather than for the equipment and software needed to provide resources. It's like paying only for cell phone minutes you use instead of paying for the towers and switching equipment needed to make your phone work. The word cloud is used to obscure the details of equipment and software that actually provide resources. For the most part, customers don't care whether equipment consists of Windows or Linux servers, large tower computers, or rack- mounted computers, as long it works. For many companies, cloud computing's allure is based on the following benefits: reduced physical plant cost, recude upfront cost, and reduced personnel costs. Although cloud computing has seemingly limitless applications, three main categories of cloud computing have taken center stage:

Software as a service
Platform as a service
Infrastructure as a service

The prhase as a service simply means that the resource resides on another server or network than the one using the resource, and customers use it as a paid service. You might also hear the term SPI model, which is based on the combination of the three aforementioned "as a service" terms (Software, Platform, Infrastructure).

Software as a Service

Software as a service (SaaS) is also called hosted applications or on-demand applications becasue the customer doesn't actually buy any software that's installed on its own equipment. Instead, the customer pays for the use of applications that run on a service provider's network.The most wellknown examples are Google Apps and Microsoft Office 365.

Platform as a Service

Platform as a service (PaaS)—aslo called hosted platform—is similar to SaaS, but the customer develops aplications with the service provider's tool and infrastructure. After applications are developed, they can be delivered to the customer's users from the provider's servers. This setup differs from SaaS, in which the service provider owns the applications delivered to users; with PaaS, the customer develops and owns the application and then delivers it to a third party. The most common PaaS products are Salesforce.com's Apex, Azure for Windows, Google's App Engine for Python and Java, WaveMaker for Ajax, and Engine Yard for Ruby on Rails.

Infrastructure as a Service

Infrastructure as a service (IaaS), or hosted infrastructure, allows companies to use a vendor's storage or even entire virtual servers as needed. Traditionally, if a company needs another 100GB of storage to house a new database, it has to buy a new hard drive—assuming the server can accommodate a new hard drive. By using IaaS, the company simply pays for another 100GB of space without worrying about how the space is actually provided. In addition, if a customer needs another server to handle its application workload, it simply pays for the amount of processing and storage the additional server actually requires instead of paying for the physical device. In most cases, IaaS run as virutal machines on more powerful physical servers.

Configuring a Network Connection

The Fundamentals of Network Communication

A computer network consists of two or more computers connected by some kind of transmission medium, such as a cable or airwaves. After they're connected, correctly configured computers can communicate with one another. The primary motivations for networking are to share resources, such as printers and hard drives; to share information, such as word-processing files; and to communicate by using applications such as e-mail. These motivations are important, especially for businesses, but another motivating factor for both businesses and home users is to "get online"—to access the Internet.

Network Components

These are the required components to network a computer:

Network interface card (NIC)—A NIC (pronounced nick) is an add-on card that's plugged into a motherboard expansion slot and provides a connection between the computer and the network. Most computers have a NIC built into the motherboard, so an additional card is not necessary.

Network medium—This cable plugs into the NIC and makes the connection between a computer and the rest of the network. In networks with just two computers, the other end of the cable can plug into the second computer's NIC. More likely, the other end of the cable plugs into an interconnecting device that accommodates several computer connections. Network media can also be airwaves, as in wireless networks. In this case, the connection is made between the antenna on the NIC and the antenna on another NIC or interconnecting device.

Interconnecting device—Although this component isn't always necessary becasue two computers can be connected directly with a cable and small wireless networks can be configured without an interconnecting device, most networks include one or several of these components. They allow computers to communicate on a network without being connected directly. Interconnecting devices include switches, hubs, routers, and wireless access point.

The preceding hardware components make a stand-alone computer into a networked computer, but software is also needed to interact with network hardware and communicate with other computers on the network. Network software transform a stand-alone OS into a network OS. It's the software that allows a word-processing program to open a document on a server and knows how to request a Web page or send an e-mail. It's also the software that communicates between the OS and network hardware.

Network software can be divided into the following:

Network clients and servers—Network client software request information that's stored on another network computer or device. Network server software allows a computer to share its resources by responding to resource request generated by network clients. Network client software can be an integral part of well-known aplications, such as Web browsers and e-mail programs.

Protocols—When clients and servers need to send information on the network, they must pass it to network protocols, which define the rules and formats a computer must use when sending information accross the network. A network protocol can be likened to a human language. Just as two people communicate by speaking the same language, two computers communicate by using the same protocol. An example of a network protocol is TCP/IP. Network protocols perform all the behind-the-scenes tasks required to handle networking functions and most of their complexity.

NIC device driver—After the network protocol has formatted a message correctly, it hands the data off to the NIC driver for transmission onto the network. NIC drivers receive data from protocols and then forward it to the physical NIC, which transmist the data onto the medium. The revese is also true. When data arrives at the NIC from the medium, the NIC hands it off to the NIC driver, which then hands it off to the network protocols. Every NIC installed in a computer must have an associated device driver installed in the OS. The device driver software manages the details of communicating wiht the NIC hardware to send data to network media and receive data from it.