December, 2007

Some time ago, somebody clicked the "Contact me" link in the navigation bar, and despite the warnings, asked a technical question. I responded, "If you have a question you can post it to the suggestion box." The reply:

Please, don't use a bot which pretends to be you to answer e-mails. Especially such a poorly-designed one.

Maybe those people were right. Perhaps I'm a robot. (It would certainly be a lot easier for me if I were.)

Steve Makofsky found this article on how you can assemble a 10-day survival pack to keep in your car for just $25. Possible Christmas gift idea? Who knows.

Don't forget the duct tape.

For good or ill, email is the most heavily used communication system at Microsoft, so much so that most people at Microsoft are known by their email addresses, sometimes more so than by their legal names! For example, most everybody at Microsoft knows Stephen Toulouse by his email address, "stepto" (pronounced as if it were spelled "steptoe"). Notice that the name of his personal domain is www.stepto.com; he has basically adopted his email address as his persona. This example is hardly an unusual one of how one's identity becomes wrapped up in one's email address. It's more likely to happen if your email address results in something catchy and easy-to-say (like stepto). Though most people don't take to this extreme; he tells me that he doesn't typically respond to the name "Stephen" any more!

All this is a rather long set-up for today's story, which is an amusing look at what happens when somebody new to the company hasn't quite incorporated the Microsoft email culture into their world view. The names have been changed, of course, but the essence of the story is true.

From: X
To: Y
Subject: What is adamsmit's email address, I need some bug info

Thanks in advance.

Y manages to keep a straight face in the reply.

From: Y
To: X
Subject: RE: What is adamsmit's email address, I need some bug info
Cc: Adam Smith (adamsmit@microsoft.com)

adamsmit

Todd Gallagher answers the weird sports questions you always wondered but knew were too stupid even to ask. Think of it as the sports version of Mythbusters.

• Would a team of midgets be the greatest offense in baseball history, because they would draw walk after walk after walk?
• Could a morbidly obese goalie shut out an NHL team?
• Could an average person beat a professional tennis player if the pro had to use a frying pan instead of a racquet?

Well, he sort of gives away the answer to the last question in the title of his book, Andy Roddick Beat Me with a Frying Pan. The stories behind how he set about finding the answers to these absurd questions are even more entertaining than the answers themselves! Here's an interview with Only a Game's Bill Littlefield. [Direct link - Real format]

On a somewhat concidental note, tonight I'm going to watch the Seattle Thunderbirds take on the Tri-City Americans, making good on my earlier admission of the possibility of seeing another hockey game. Hopefully with normal-sized goalies.

Although the theoretical maximum file size on NTFS is 2⁶⁴−1 clusters, the current implementation of the NTFS driver supports files up to "only" 16TB minus 64KB. (In other words, the disk format supports files up to 2⁶⁴−1 clusters, but the current drivers won't go above 16TB−64KB.)

Back in 2002, in order to verify that the drivers did indeed support files as big as their design maximum, the NTFS test team sat down, created a volume slightly bigger than 16TB, and then created a file of the maximum supported size, filling it with a known pattern. After the file was successfully created, they then ran another program that read the entire file back into memory and verified that the contents were correct. (They ran other tests, too, of course, but those are the ones that are important to this story.)

How long did it take to create this nearly-16TB file?

Around three days.

Verifying that the data was written correctly took about four days.

(Yes, it's strange that reading was slower than writing. I don't know why, but I can guess and so can you. Maybe the read test did a bunch of extra verification. Maybe the read test used random access as well as sequential access. Or maybe there was just rounding error in the reporting of the duration. I wasn't there, so I don't know for sure.)

Back in 16-bit Windows, MS-DOS cast a long and dark shadow. The really ugly low-level munging was very much in the MS-DOS spirit. You opened files by setting up registers and issuing an int 21h, just like in MS-DOS. Although the interrupt went to Windows instead, Windows maintained the MS-DOS calling convention. Process startup followed the same "real men write in assembly language" philosophy.

All the parameters to a 16-bit program were passed in registers. The entry point to a 16-bit process received the following parameters on Windows 3.1:

Hey, nobody said that 16-bit Windows was designed for portability.

The first thing a 16-bit program did was call the InitTask function. This function receives its parameters in registers, precisely in the format that they are received by the program entry point. The InitTask function initializes the stack, the data segment, the heap, retrieves and prepares the command line, recovers the nCmdShow parameter that was passed to WinExec, all the normal startup stuff. It even edits the stack of the caller so that real-mode stack walking works (critical for memory management in real-mode). When InitTask is all finished, it returns with the registers set for the next phase:

Once InitTask returns, the stack, heap, and data segment are "ready to run," and if you have no other preparations to do, you can head right for the application's WinMain function. Minimal startup code therefore would go like this:

    call    far InitTask
    test    ax, ax
    jz      exit
    push    di      ; hInstance
    push    si      ; hPrevInstance
    push    es      ; lpszCmdLine selector
    push    bx      ; lpszCmdLine offset
    push    dx      ; nCmdShow

    ... some lines of code that aren't important to the discussion ...

    call    far WinMain ; call the application's WinMain function

    ; return value from WinMain is in the AL register,
    ; conveniently positioned for the exit process coming up next

exit:
    mov     ah, 4Ch ; exit process function code
    int     21h     ; do it

Why wasn't the application entry point called main? Well, for one thing, the name main was already taken, and Windows didn't have the authority to reserve an alternate definition. There was no C language standardization committee back then; C was what Dennis said it was, and it was hardly guaranteed that Dennis would take any special steps to preserve Windows source code compatibility in any future version of the C language. Since K&R didn't specify that implementations could extend the acceptable forms of the main function, it was entirely possible that there was a legal C compiler that rejected programs that declared main incorrectly. The current C language standard explicitly permits implementation-specific alternate definitions for main, but requiring all compilers to support this new Windows-specific version in order to compile Windows programs would gratuitously restrict the set of compilers you could use for writing Windows programs.

If you managed to overcome that obstacle, you'd have the problem that the Windows version of main would have to be something like this:

int main(int argc, char *argv[], HINSTANCE hinst,
         HINSTANCE hinstPrev, int nCmdShow);

Due to the way C linkage was performed, all variations of a function had to agree on the parameters they had in common. This means that the Windows version would have to add its parameters onto the end of the longest existing version of main, and then you'd have to cross your fingers and hope that the C language never added another alternate version of main. If you went this route, your crossed fingers failed you, because it turns out that a third parameter was added to main some time later, and it conflicted with your Windows-friendly version.

Suppose you managed to convince Dennis not to allow that three-parameter version of main. You still have to come up with those first two parameters, which means that every program's startup code needs to contain a command line parser. Back in the 16-bit days, people scrimped to save every byte. Telling them, "Oh, and all your programs are going to be 2KB bigger" probably wouldn't make you a lot of friends. I mean, that's four sectors of I/O off a floppy disk!

But probably the reason why the Windows entry point was given a different name is to emphasize that it's a different execution environment. If it were called main, people would take C programs designed for a console environment, throw them into their Windows compiler, and then run them, with disastrous results.