Lesson #35 - An Introduction To DOS/Windows

When the A+ program was first introduced, the standards for operating systems were a fair amount different from what we know now.  Each computer company used their own proprietary ROM operating systems to start their computers, and software ran from these BIOS-driven systems.

The Beginnings of DOS

The original DOS program was designed to give a standardization to how a computer ran.  It was a cross-platform interface that used specific rules to allow programs to interface with.  By using the operating system as a medium between the hardware and the software, it became easier to write programs for a wide range of computer systems.  It standardized the computer landscape into a single useable format.

Windows is an extension of the DOS system.  Where DOS was a text-driven operating system, Windows offers a graphical user interface (GUI) system that makes computers both easier to use and more powerful to write programs for.  With the introduction of Windows 95, DOS became totally obsolete, and is no longer used in Windows 98, ME, or 2000.  

For the pre-2000 series A+ exam you were required to know certain aspects of the DOS/Windows word.  The current A+ exam doesn't require the DOS knowledge any more, and only requires Command Prompt, Windows 9x, and Windows 2000 knowledge.  Today I'm going to give a short tutorial on some of the old DOS/Windows knowledge only as a backdrop for next week's lesson on Windows.

Command Prompt

As we said before, DOS is a text-line operating system.  There was no mouse used to click icons in the DOS word.  Commands were typed in on the keyboard at the command prompt (c:>), and the only time you had graphics was if the program you were running allowed them.

DOS also was not a multi-tasking operating system.  It ran programs one at a time.  If you wanted to open a file in another application, you had to close down the application you were running and then open the new application.  Can you see why Windows was such an improvement yet?

The other major difference you'll notice with DOS is that it didn't have any virtual memory.  In fact, DOS was limited in many ways in the way it used conventional RAM technologies, and the concept of Virtual Memory wasn't brought about until Windows came about.

File Systems

One major change that you will see on the exam is filing systems.  File systems tell the hard drive and the operating system how to store information.  They use File Allocation Tables (FAT) to state how information is spread out on a hard drive, and tell the drive how to retrieve that information later.

DOS used a simple FAT system that supported 16 bit entries.  When Windows 95 came around, it used something called VFAT, or Virtual File Allocation Table.  This was a 32 bit filing system that supported long file names, beyond the 16 character limitations of DOS.  Later versions of Windows support FAT32, a more complex FAT system, and NTFS, which is the NT filing system.

DOS Memory List

To finish off today, I'm going to give you some quick facts about DOS that might not directly be on the test but will help you remember key elements about the DOS/Windows environment.

•  The DOS root directory is limited to 512 files.

• DOS has 3 memory areas - Conventional Memory (below 640K), Expanded or Upper Memory (between 640K and 1MB) and Extended Memory (above 1MB)

• DOS used a high memory system that consisted of the first 64K of extended memory.

• EMM386.EXE enables expanded memory and the use of upper memory as system memory.  

• HIMEM.SYS is the driver used to allow DOS to use Expanded and Extended Memory (Above 640K)

• ****VERY IMPORTANT****  The DOS boot sequence is IO.SYS, MSDOS.SYS, CONFIG.SYS, COMMAND.COM, AUTOEXEC.BAT

• Device Drivers in DOS are loaded through the CONFIG.SYS file, although this file DOES NOT need to be present to load DOS.  Device Drivers are loaded as TSRs, or Terminate-Stay Resident programs.

• COMMAND.COM is the program that creates the command prompt (c:>)

• To change the attributes of any DOS file or folder, use the ATTRIB command.  To delete a folder with all it's files and subdirectories, use the DELTREE command.

• For Windows 3.X to run, you run DOS first.  Windows 9X does not require DOS, but instead runs a DOS emulator to allow you to run older DOS applications.

That is all you should need to know about DOS.  Next week we're going to look deep into the Windows world and find out how it varies from DOS, and what you need to know about Windows to pass the OS section of the A+ exam.