Earlier this week (May 5) Microsoft Windows 7 Release Candidate was released to the general public and like many technology enthusiasts I downloaded a copy early in the morning hours on Tuesday, shortly after Microsoft made it available on its website.

The RC build of Windows 7 (build 7100) has many tweaks over the previous beta build I have (build 7000) and I have not yet played with it long enough to come up with any meaningful conclusions. However, this is not the point of this article. As you might have noticed from the title of this article, I was not about to talk about my experience with Windows 7 (maybe I will write about it later). What I noticed the first thing in Windows 7 is that the DEBUG command is nowhere to be found.

I was just old enough to remember the very early days of DEBUG under MS-DOS. In fact, I was fascinated with such a small and yet powerful tool that came with every version of MS-DOS distribution. the DEBUG command was so powerful that you could do almost anything with your machine with sometimes just a few key strokes.

For a long time, I used DEBUG to learn x86 assembly language and to learn about disk (both floppy disks and harddrives) structures and file systems. And occasionally, I would use DEBUG to edit binary files.

I remembered that I could use commands like

-l 100 0 0 1

to load the boot sector from floppy A and inspect whether the boot sector was infected with any virus and if so, I would find a clean floppy disk and using DEBUG to write its boot sector to the disk that was infected.

And routinely, I would use the following commands to inspect the partition table of my harddrive to make sure that it was free from any infections:

mov ax, 0201
mov bx, 1000
mov cx, 0001
mov dx, 0080
int 13
int 3
-g 100
-d 1000

Remember this one?

jmp ffff:0000

I remembered that someone at my high school used to play the pranks by changing the very first few bytes on floppy disks to EA:00:00:FF and placed the disks in computers in the lab so that whenever someone turned on the computer, it would enter an infinite reboot cycle.

And when CIH stroke in the late nineties, my friends and I would use DEBUG to inspect the virus’s code to see how the instructions could actually be used to cause real physical damage to the hardware.

After Windows came along, I still used DEBUG often. After all, deep inside Windows (up till Windows ME), there was MS-DOS and for years, user were allowed to operate in real mode if they so inclined to. With the advent of Windows 2000 and then later Windows XP people started to forget about DEBUG since the operating system became true 32bit and the DOS prompt became just an emulator. You could still view files and write assembly code within DEBUG, but it was in a protected environment and everything you do was pretty safe and you couldn’t really do anything harmful to the hardware (of course, you could still overwrite sectors in floppy disks if you wanted to).

Ah, those were the good old days. Just like QBasic disappeared from later versions MS-DOS, DEBUG has gradually become obsolete. It remained in Windows Vista, but it is no where to be found in Windows 7. At last, Windows has shed one of its last vintage applications from the MS-DOS era.

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