View Full Version : 16 bit dos application

March 21st, 2008, 08:01
this is my first post to this forum
plz forgive me for any mistake

i have a dos based accounting software which i Harv to renew every year
recently i got a new pc and moved all my file to my new sys except this software i Harv setup of this program but every time we run that it generate a new key and corresponding that key we have to enter pass key.
i want to do something about it i have tried to load in ollydbg, but olly refused to load it with error that file is not a 32 bit executable when i clicked try to load it any way . when i executed the code freely ntvdm.exe pop up and then setup starts and than crashes
after that i have searched but cant find sol or any thing regrading this
can somebody tell me which type of disassembler should be used with 16 bit dos app.

March 21st, 2008, 09:59
It is apparent that you did NOT actually Read The FAQ or you would know that you should have actually searched on the net for a "disassembler for DOS applications" or you would have found several and numerous tutorials that might assist you.

So how about YOU put "disassembler dos applications" in your favorite search engine and YOU read some of the hits you will get!

In order to do what you want to do, you will need some understanding of assembly language instructions. There are many primers available, some of them listed in the links below.

You have alot to learn if you are going to start reversing the software and your need to start that learning process by YOU doing alot of studying. This is not a place where someone will teach you what you need to learn, but we will give you a helping hand as YOU make the effort to learn what you need to know. First YOU have to do some of the work, including your own basic research.


March 21st, 2008, 11:06
Thanks for the sugg.

March 21st, 2008, 11:30
i hav gone thur FAQ's,tutorial and i know assembly lang.
my problem is that i cant make apporach to reverse tht keygen of setup
i m really interseted in reverse engg. and want to learn it any how i think that my target is really hard for me at this time
i will for that after some time between this if any one intersted and know anything related to dos reversing plz let me know.

March 21st, 2008, 12:16
Dos reversing is a fading art, along with such a gem of an operating system.
ExeTools has a forum dedicated to DOS reversing, but the last time someone publish anything in there was a year ago.

Now: DOS reversing: The protections tended to be naive.
-You need to learn the 16 bit memory management,
-you can disassemble a 16 bit file with IDA.
-you won't get very far doing debugging work on a pure 32 bit Environment. Do your debugging in an old machine running DOS or Windows 95 using either an old version of SoftIce or one of the old DOS debuggers.

March 21st, 2008, 12:47
Find out Turbo debugger and work on it. Its quite good.

There are many sites world wide that allow you to download FREELY, original microsoft DOS

1. Download Microsoft DOS
2. Download VMWARE
3. TRY and run DOS on VMWARE...if not, try Win98
4. Download SoftICe for DOS OR, v3.x for win98.
5. Debug to heart's content...

Have Phun

March 22nd, 2008, 18:10
[Originally Posted by zmintu;73498]i hav gone thur FAQ's
I got this by typing 'wldr +dos' in Google:


Of course, I knew about wldr, but what you need is in the RCE archives.

Softice still has a util16 directory that contains the apps dldr.exe and wldr.exe. These apps can be used even in XP to debug?? 16 bit DOS and NE files.

It sounds to me like you're looking for a quick fix. Whereas that is a good way to learn, it will take 'many' hours of study and ingenuity to get there.