PC Operating Systems

Once loaded, the operating system's tasks fall into six broad categories:
• Processor management - Breaking the tasks down into manageable chunks and prioritizing them before sending to the CPU
• Memory management - Coordinating the flow of data in and out of RAM and determining when virtual memory is necessary
• Device management - Providing an interface between each device connected to the computer, the CPU and applications
• Storage management - Directing where data will be stored permanently on hard drives and other forms of storage
• Application Interface - Providing a standard communications and data exchange between software programs and the computer
• User Interface - Providing a way for you to communicate and interact with the computer
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Say, for example, that you open up a word processing program and type a letter, save it and then print it out. Several components work together to make this happen:
 The keyboard and mouse send your input to the operating system.
 The operating system determines that the word-processing program is the active program and accepts your input as data for that program.
 The word-processing program determines the format that the data is in and, via the operating system, stores it temporarily in RAM.
 Each instruction from the word-processing program is sent by the operating system to the CPU. These instructions are intertwined with instructions from other programs that the operating system is overseeing before being sent to the CPU.
 All this time, the operating system is steadily providing display information to the graphics card, directing what will be displayed on the monitor.
 When you choose to save the letter, the word-processing program sends a request to the operating system, which then provides a standard window for selecting where you wish to save the information and what you want to call it. Once you have chosen the name and file path, the operating system directs the data from RAM to the appropriate storage device.
 You click on "Print." The word-processing program sends a request to the operating system, which translates the data into a format the printer understands and directs the data from RAM to the appropriate port for the printer you requested.
 You open up a Web browser and check out HowStuffWorks. Once again, the operating system coordinates all of the action. This time, though, the computer receives input from another source, the Internet, as well as from you. The operating system seamlessly integrates all incoming and outgoing information.
 You close the Web browser and choose the "Shut Down" option.
 The operating system closes all programs that are currently active. If a program has unsaved information, you're given an opportunity to save it before closing the program.
 The operating system writes its current settings to a special configuration file so that it will boot up next time with the same settings.
 If the computer provides software control of power, then the operating system will completely turn off the computer when it finishes its own shut-down cycle. Otherwise, you will have to turn the power off manually.
We'll look at the future of PCs next.

Powering Up a PC

A typical computer session begins with turning on the power. Here's what happens in that process:
1. You press the "On" button on the computer and the monitor.
2. You see the BIOS software doing its thing, called the power-on self-test (POST). On many machines, the BIOS displays text describing such data as the amount of memory installed in your computer and the type of hard disk you have. During this boot sequence, the BIOS does a remarkable amount of work to get your computer ready to run.
• The BIOS determines whether the video card is operational. Most video cards have a miniature BIOS of their own that initializes the memory and graphics processor on the card. If they don't, there is usually video-driver information on another ROM on the motherboard that the BIOS can load.
• The BIOS checks to see if this is a cold boot or a reboot. It does this by checking the value at memory address 0000:0472. A value of 1234h indicates a reboot, in which case the BIOS skips the rest of POST. Any other value is considered a cold boot.
• If your computer is undergoing a cold boot, the BIOS verifies RAM by performing a read/write test of each memory address. It checks for a keyboard and a mouse. It looks for an expansion bus and, if it finds one, checks all the connected cards. If the BIOS finds any errors during the POST, it notifies you with a series of beeps or a text message displayed on the screen. An error at this point is almost always a hardware problem.
• The BIOS displays some details about your system. This typically includes information about the following:
o Processor
o Floppy and hard drive
o Memory
o BIOS revision and date
o Display
• Any special drivers, such as those for expansion cards, are loaded from the adapter and the BIOS displays the information.
• The BIOS looks at the sequence of storage devices identified as boot devices in the complementary metal-oxide semiconductor (CMOS) setup. Boot is short for "bootstrap," as in the old phrase "Pull yourself up by your bootstraps." Boot refers to the process of launching the operating system. The BIOS tries to initiate the boot sequence from the first device using the bootstrap loader.
3. The bootstrap loader loads the operating system into memory and allows it to begin operation. It does this by setting up the divisions of memory that hold the operating system, user information and applications. The bootstrap loader then establishes the data structures that are used to communicate within and between the sub-systems and applications of the computer. Finally, it turns control of the computer over to the operating system.

PC Connections

A typical computer connects to the world around it in three different ways: input/output devices, ports and networking.
No matter how powerful the components inside your computer are, you need a way to interact with them. This interaction is called input/output (I/O). The most common types of I/O in PCs are:
• Monitor - The monitor is the primary device for displaying information from the computer.
• Keyboard - The keyboard is the primary device for entering information into the computer.
• Mouse - The mouse is the primary device for navigating and interacting with the computer.
• Removable storage - Removable storage devices allow you to add new information to your computer very easily, as well as save information that you want to carry to a different location. There are several types of removable storage:
o CD-ROM - CD-ROM (compact disc, read-only memory) is a popular form of distribution of commercial software. Many systems now offer CD-R (recordable) and CD-RW (rewritable), which can also record. CD-RW discs can be erased and rewritten many times.
o Flash memory - Based on a type of ROM called electrically erasable programmable read-only memory (EEPROM), Flash memory provides fast, permanent storage. CompactFlash, SmartMedia and PCMCIA cards are all types of Flash memory.
o DVD-ROM - DVD-ROM (digital versatile disc, read-only memory) is similar to CD-ROM but is capable of holding much more information.

You may use Bluetooth or Wi-Fi to sync your music player or print driving directions, but many computers still have ports to help you connect to a wide selection of peripherals. While there have been others, two are most commonly found on newer computers:
• Universal Serial Bus (USB) - The most popular external connection, USB ports offer power and versatility and are incredibly easy to use.
• FireWire (IEEE 1394) - FireWire is a very popular method of connecting digital-video devices, such as camcorders or digital cameras, to your computer.
Networking, especially to the Internet, is very important to today's computer users. Your computer can probably use one or more of these methods:
• Modem - This is the standard method of connecting to the Internet.
• Local area network (LAN) card - This is used by many computers, particularly those in an Ethernet office network, to connect to one another.
• Cable modem - This type of modem uses the cable system in your home, like the kind you might use to subscribe to cable TV, to connect to the Internet.
• Digital Subscriber Line (DSL) modem - This is a high-speed connection that works over a standard telephone line.
• Very high bit-rate DSL (VDSL) modem - A newer variation of DSL, VDSL requires that your phone line have fiber-optic cables. An even faster version called the gigabit per second DSL (GDSL) may follow [source: Cioffi, et al.].
Now that you're familiar with the parts of a PC, let's see what happens in a typical computer session.

How PCs Work

When you mention the word "technology," most people think about computers. Virtually every facet of our lives has some computerized component. The appliances in our homes have microprocessors built into them, as do our televisions. Even our cars have computers. But the computer that everyone thinks of first is typically the personal computer, or PC.
A PC is a general-purpose tool built around a microprocessor. It has lots of different parts -- including memory, a hard disk, a modem, and more -- that work together. "General purpose" means that you can do many different things with a PC. You can use it to type documents, send e-mail, browse the Internet and play games.
PCs trace their history back to the 1970s, when a man named Ed Roberts began to sell computer kits based on a microprocessor chip designed by Intel. Roberts called his computer the Altair 8800 and sold the unassembled kits for $395. Popular Electronics ran a story about the kid in its January 1975 issue, and to the surprise of just about everyone, the kits became an instant hit and the era of the personal computer began [source: The Computer History Project].
A few years¬ later, the dynamic duo of Steve Jobs and Steve Wozniak unleashed the Apple II computer on the world. From that point on, the personal computer really began to take off. Other manufacturers followed suit, and soon there were computers from Commodore, Atari and Texas Instruments. Not long after the debut of the Apple II, IBM got into the personal computer game. ¬
¬Today, when someone says PC, chances are they mean a machine running on the Microsoft Windows operating system with an x86-compatible microprocessor. While Apple Macintosh computers are technically personal computers, most people wouldn't call them PCs.
In this article, we will talk about PCs in the general sense and all the different parts that go into them. You'll learn about the various components and how they work together in a basic operating session. You'll also find out what the future may hold for these machines. ¬ ¬
PC Parts
Let's take a look at the main components of a typical desktop computer:
• Central processing unit (CPU) - The microprocessor "brain" of the computer system is called the central processing unit. It's a chip that holds a complete computational engine. It uses assembly language as its native language. Everything that a computer does is overseen by the CPU.
• Memory - This is very fast storage used to hold data. It has to be fast because it connects directly to the microprocessor. There are several specific types of memory in a computer:
• Random-access memory (RAM) - Used to temporarily store information with which the computer is currently working
• Read-only memory (ROM) - A permanent type of memory storage used by the computer for important data that doesn't change
• Basic input/output system (BIOS) - A type of ROM that is used by the computer to establish basic communication when the computer is first powered on
• Caching - The storing of frequently used data in extremely fast RAM that connects directly to the CPU
• Virtual memory - Space on a hard disk used to temporarily store data and swap it in and out of RAM as needed
• Flash memory - a solid state storage device, Flash memory requires no moving parts and retains data even after the computer powers off
Motherboard - This is the main circuit board to which all of the other internal components connect. The CPU and memory are usually on the motherboard. Other systems may be found directly on the motherboard or connected to it through a secondary connection. For example, a sound card can be built into the motherboard or connected through an expansion slot.
• Power supply - An electrical transformer regulates the electricity used by the computer.
• Hard disk - This is large-capacity permanent storage used to hold information such as programs and documents. Traditional hard drives contain moving parts -- the drive has platters on which it stores data. The drive spins the platters to record and read data. But some newer hard drives are flash-based with no moving parts. These drives are called solid-state drives.
• Operating system - This is the basic software that allows the user to interface with the computer.
• Integrated Drive Electronics (IDE) Controller - This is the primary interface for the hard drive, CD-ROM and floppy disk drive.
• Accelerated Graphics Port (AGP) - This is a very high-speed connection used by the graphics card to interface with the computer.
• Sound card - This is used by the computer to record and play audio by converting analog sound into digital information and back again.
• Graphics card - This translates image data from the computer into a format that can be displayed by the monitor. Some graphics cards have their own powerful processing units (called a GPU -- graphics processing unit). The GPU can handle operations that normally would require the CPU.
• Ports - In computer hardware terms, a port is an interface that allows a computer to communicate with peripheral equipment.

• Real-time clock - Every PC has a clock containing a vibrating crystal. By referring to this clock, all the components in a computer can synchronize properly.
• Complementary Metal-oxide Semiconductor - The CMOS and CMOS battery allow a computer to store information even when the computer powers down. The battery provides uninterrupted power.
• Fans, heat sinks and cooling systems - The components in a computer generate heat. As heat rises, performance can suffer. Cooling systems keep computers from overheating.
In the next section, we'll look at how your computer connects to the outside world.

How PCI Express Works

Peripheral Component Interconnect (PCI) slots are such an integral part of a computer's architecture that most people take them for granted. For years, PCI has been a versatile, functional way to connect sound, video and network cards to a motherboard.
But PCI has some shortcomings. As processors, video cards, sound cards and networks have gotten faster and more powerful, PCI has stayed the same. It has a fixed width of 32 bits and can handle only 5 devices at a time. The newer, 64-bit PCI-X bus provides more bandwidth, but its greater width compounds some of PCI's other issues.
A new protocol called PCI Express (PCIe) eliminates a lot of these shortcomings, provides more bandwidth and is compatible with existing operating systems. In this article, we'll examine what makes PCIe different from PCI. We'll also look at how PCI Express makes a computer faster, can potentially add graphics performance, and can replace the AGP slot.

High-Speed Serial Connection
In the early days of computing, a vast amount of data moved over serial connections. Computers separated data into packets and then moved the packets from one place to another one at a time. Serial connections were reliable but slow, so manufacturers began using parallel connections to send multiple pieces of data simultaneously.
It turns out that parallel connections have their own problems as speeds get higher and higher -- for example, wires can interfere with each other electromagnetically -- so now the pendulum is swinging back toward highly-optimized serial connections. Improvements to hardware and to the process of dividing, labeling and reassembling packets have led to much faster serial connections, such as USB 2.0 and FireWire.
PCI Express is a serial connection that operates more like a network than a bus. Instead of one bus that handles data from multiple sources, PCIe has a switch that controls several point-to-point serial connections. (See How LAN Switches Work for details.) These connections fan out from the switch, leading directly to the devices where the data needs to go. Every device has its own dedicated connection, so devices no longer share bandwidth like they do on a normal bus. We'll look at how this happens in the next section.

Before the Internet

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In the 1950s and early 1960s, prior to the widespread inter-networking that led to the Internet, most communication networks were limited in that they only allowed communications between the stations on the network. Some networks had gateways or bridges between them, but these bridges were often limited or built specifically for a single use. One prevalent computer networking method was based on the central mainframe method, simply allowing its terminals to be connected via long leased lines. This method was used in the 1950s by Project RAND to support researchers such as Herbert Simon, at Carnegie Mellon University in Pittsburgh, Pennsylvania, when collaborating across the continent with researchers in Sullivan, Illinois, on automated theorem proving and artificial intelligence.
Three terminals and an ARPfb
Main articles: RAND and ARPANET
A fundamental pioneer in the call for a global network, J.C.R. Licklider, articulated the ideas in his January 1960 paper, Man-Computer Symbiosis.
"A network of such [computers], connected to one another by wide-band communication lines [which provided] the functions of present-day libraries together with anticipated advances in information storage and retrieval and [other] symbiotic functions."
—J.C.R. Licklider, [2]
In October 1962, Licklider was appointed head of the United States Department of Defense's Advanced Research Projects Agency, now known as DARPA, within the information processing office. There he formed an informal group within DARPA to further computer research. As part of the information processing office's role, three network terminals had been installed: one for System Development Corporation in Santa Monica, one for Project Genie at the University of California, Berkeley and one for the Compatible Time-Sharing System project at the Massachusetts Institute of Technology (MIT). Licklider's identified need for inter-networking would be made obvious by the apparent waste of resources this caused.
"For each of these three terminals, I had three different sets of user commands. So if I was talking online with someone at S.D.C. and I wanted to talk to someone I knew at Berkeley or M.I.T. about this, I had to get up from the S.D.C. terminal, go over and log into the other terminal and get in touch with them. [...] I said, it's obvious what to do (But I don't want to do it): If you have these three terminals, there ought to be one terminal that goes anywhere you want to go where you have interactive computing. That idea is the ARPAnet."
—Robert W. Taylor, co-writer with Licklider of "The Computer as a Communications Device", in an interview with the New York Times, [3]
Packet switching
Main article: Packet switching
At the tip of the internetworking problem lay the issue of connecting separate physical networks to form one logical network. During the 1960s, Paul Baran (RAND Corporation), produced a study of surviveable networks for the US military. This was based on small 'message-blocks' Donald Davies (National Physical Laboratory, UK), proposed and developed a network based on packet-switching, a technology which had also been studied and analysed by Leonard Kleinrock (MIT). Packet-switching provided better bandwidth utilization and response times than the traditional cicuit-switching technology used for telephony, particularly on resource-limited interconnection links.
Packet switching is a rapid store-and-forward networking design that divides messages up into arbitrary packets, with routing decisions made per-packet. Early networks used message switched systems that required rigid routing structures prone to single point of failure. This led Paul Baran's US Military funded research to focus on using message-blocks to include network redundancy,[4] which in turn led to the widespread urban legend that the Internet was designed to resist nuclear attack

History of the Internet

Before the wide spread of internetworking that led to the Internet, most communication networks were limited by their nature to only allow communications between the stations on the local network and the prevalent computer networking method was based on the central mainframe computer model. Several research programs began to explore and articulate principles of networking between physically separate networks, leading to the development of the packet switching model of digital networking. These research efforts included those of the laboratories of Donald Davies (NPL), Paul Baran (RAND Corporation), and Leonard Kleinrock at MIT and at UCLA. The research led to the development of several packet-switched networking solutions in the late 1960s and 1970s,[1] including ARPANET and the X.25 protocols. Additionally, public access and hobbyist networking systems grew in popularity, including unix-to-unix copy (UUCP) and FidoNet. They were however still disjointed separate networks, served only by limited gateways between networks. This led to the application of packet switching to develop a protocol for internetworking, where multiple different networks could be joined together into a super-framework of networks. By defining a simple common network system, the Internet Protocol Suite, the concept of the network could be separated from its physical implementation. This spread of internetworking began to form into the idea of a global network that would be called the Internet, based on standardized protocols officially implemented in 1982. Adoption and interconnection occurred quickly across the advanced telecommunication networks of the western world, and then began to penetrate into the rest of the world as it became the de-facto international standard for the global network. However, the disparity of growth between advanced nations and the third-world countries led to a digital divide that is still a concern today.
Following commercialization and introduction of privately run Internet service providers in the 1980s, and the Internet's expansion for popular use in the 1990s, the Internet has had a drastic impact on culture and commerce. This includes the rise of near instant communication by electronic mail (e-mail), text based discussion forums, and the World Wide Web. Investor speculation in new markets provided by these innovations would also lead to the inflation and subsequent collapse of the Dot-com bubble. But despite this, the Internet continues to grow.