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