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