| Permission is granted for the below article to | | | | command lineinterface that lets users communicate |
| forward,reprint, distribute, use for ezine, newsletter, | | | | more directly withthe operating system and with |
| website,offer as free bonus or part of a product for | | | | hardware devices through the |
| sale as longas no changes are made and the byline, | | | | BIOS. The most familiar command line interface is the |
| copyright, and theresource box below is included. | | | | DOS |
| Understanding the Software Layers of a Computer | | | | Command Prompt. |
| By Stephen Bucaro | | | | At the DOS command prompt you can type "print" |
| You're typing in a word processor and you decide it | | | | followed bythe name of a document and a printed |
| wouldbe nice to have a hard copy. You select File | | | | | copy will be generated. |
| Print inthe menu and the printer comes to life, feeding | | | | But don't expect fancy fonts or formatting. Although |
| out a copyof your document on paper. It seems like a | | | | thecommand line interface can be very powerful for |
| simple process,but in reality your request passed | | | | some tasks,for other tasks it is very crude. |
| through many layers ofsoftware before reaching your | | | | When you first start your computer, it has no |
| printer. | | | | softwareloaded. You could say your computer is "brain |
| Although you requested the print through a menu of | | | | dead". Itdoesn't even know how to use the hard disk |
| yourword processing application, that application did | | | | drive to loadthe operating system. |
| notcontact the printer directly. Instead, the aplication | | | | The BIOS is non-volatile memory built into the |
| madea request to the computer's operating system. | | | | computersmotherboard. Non-volatile means that the |
| Remember,today's computers are multi-tasking. That | | | | instructions inthe memory are not lost when you turn |
| means they canperform more than one task at a time. | | | | the power off. |
| The operating systemmediates the priority of multiple | | | | When you first start your computer, it is hard-wired |
| tasks requesting to usea hardware device. | | | | tostart reading the first instruction in the BIOS. The |
| The operating system did not contact the printer | | | | BIOSis not usually all in a single chip. As the BIOS |
| directly. | | | | starts,it looks for other parts of the BIOS that reside in |
| Remember, today's computers can have a multitude | | | | chipson expansion cards. From these instructions, it |
| ofdifferent hardware attached. There are thousands | | | | learns howto check itself out (Power-on Self Test) |
| ofdifferent kinds of printers, and a computer may | | | | and how tolocate and load the operating system. The |
| haveseveral printers attached. Instead, the operating | | | | computer "BOOTS" |
| systemcommunicates with a piece of software called | | | | (pulls itself up by its bootstraps). |
| a "devicedriver", specific to the printer that you | | | | The last thing the BIOS does is locate the drive |
| selected. | | | | containingthe operating system and begin loading the |
| The device driver did not contact the printer directly. | | | | operating system. |
| Instead, the device driver contacted a program called | | | | Because the hard disk has vastly more storage |
| the | | | | capacity thana BIOS chip, the operating system |
| BIOS (Basic Input/Output System). Whereas all the | | | | software can be large andpowerful. As the operating |
| programsup to this point had been loaded from the | | | | system loads, it begins loadingdevice drivers and |
| computers harddrive, the BIOS was loaded from a | | | | configuring the hardware. |
| memory chip. Finally,the BIOS communicates directly | | | | In the early days, BIOS programs where stored in |
| with the electroniccircuits of the printer. | | | | ROM (readonly memory). Todays computers usually |
| [Application]--[Operating System]--[Device Driver]-- | | | | store BIOS programsin a type of memory, called |
| [BIOS]--[Hardware] | | | | "Flash memory" that can berewritten. This allows you |
| The above explanation describes the common | | | | to reprogram the BIOS to fixbugs, or to update it. For |
| software layersof a computer. Each of the software | | | | example, You might download a |
| layers described abovemay itself consist of many | | | | BIOS update program from the Web and run it from a |
| layers. An application maycommunicate with the | | | | floppy disk. |
| operating system through a piece ofsoftware called a | | | | The important thing to understand is that your |
| DLL (Dynamic Link Library). | | | | computer haslayers of software. You should |
| The operating system especially is constructed of | | | | understand where each layerresides in the path from |
| manylayers. Sometimes the operating system is | | | | user to hardware. You should nowunderstand that |
| described to belike an onion. At the center of the onion | | | | when you dial out with your web browser,the request |
| is the operatingsystems kernal. Only other layers of | | | | is passed to the operating system, which passesit to |
| the operating systemare allowed to communicate | | | | the modem driver, which communicates with a BIOS |
| directly with the kernal. Theouter layer of the operating | | | | onthe modem. That BIOS is the program that actually |
| system consists of programscalled services which | | | | works theelectronics of your modem. |
| applications can communicate withdirectly. | | | | Resource Box: |
| It is possible to communicate with the printer directly | | | | Copyright(C)2004 Bucaro TecHelp. |
| (well almost). Most operating systems have a | | | | |