[bigstrat2003]

One of the craziest Raymond Chen stories is one where a Windows API call would return a pointer to a data structure the OS had allocated for the operation. The programmers at Microsoft made the data structure bigger than they needed, for future expansion. But some third party devs noticed the extra space, and started to use it to store data for their program. Then when Windows tried to start using the extra space, those applications would crash.

Reasonable people can disagree on a lot of things in programming. But I still do not understand how one can consider writing to memory the OS owns to be ok. It's sheer professional malpractice to do that kind of thing. With stuff like that, I don't think that any amount of documentation would have helped. The issue was that those programmers simply did not care about anything except getting their own program working, and did whatever the most expedient method was to get there.

[acuozzo]

> But I still do not understand how one can consider writing to memory the OS owns to be ok.

Go to Vogons and look at all of the memory tricks people will use to get various games running on MS-DOS. This kind of juggling exactly which drivers to load, etc. is why Microsoft added the boot menu in MS-DOS 6.0 to CONFIG.SYS.

I'm not necessarily saying that this was the case here, but it smells like that to me.

[Hackbraten]

Back then, many programmers originally learned their ropes in an 8-bit home computer era (or earlier), where it used to be completely normal and even necessary that you used whatever memory region you got away with.

For example, on the C64, you would get away with using the memory locations $02, $2A, $52, $FB to $FE, $02A7 to $02FF, and $0313 as scratch space for your own programs. Memory was incredibly scarce. I can’t blame programmers for sticking with their habits and for taking several years to unlearn and adjust their misconceptions about who owns what if they came from a home computer era where that pattern used to be the only way to get stuff done.

[Legend2440]

>I still do not understand how one can consider writing to memory the OS owns to be ok.

Things were different back then. People did a lot of hacky stuff to fit their programs into memory, because you were genuinely constrained by hardware limitations.

Not to mention, the idea of the OS owning the machine was not as well developed as it is today. Windows 3.11 was just another program, it didn't have special permissions like modern OSes, and you would routinely bypass it to talk to the hardware directly.

[jasonfarnon]

"Not to mention, the idea of the OS owning the machine "

I agree--back then when computers had <=4MB or RAM I would've called hogging unused memory for some selfish speculative future use "professional malpractice".

[chihuahua]

Some of that attitude survives to this day:

When an OS uses any memory that's otherwise unused as a file cache, which is instantly available if an application wants more memory, but isn't shown as "unused": "This OS is terrible, I have 16GB of RAM but all of it is being used!"

When an OS doesn't do this: "This OS is terrible, I bought all this RAM and the OS doesn't use it!"

[ErroneousBosh]

> Things were different back then. People did a lot of hacky stuff to fit their programs into memory, because you were genuinely constrained by hardware limitations.

Are you going to tell them what "32-bit Clean" meant for Mac developers, or will we let them find out that particular horror movie for themselves?

[jjmarr]

> But I still do not understand how one can consider writing to memory the OS owns to be ok.

Your manager tells you to reduce memory usage of the program "or else".

[badsectoracula]

TBH i think a more likely explanation is that they needed to somehow identify separate instances of that data structure and they thought to store some ID or something in it so that when they encountered it next they'd be able to do that without keeping copies of all the data in it and then comparing their data with the system's.

[topspin]

^^ The voice of experience, here.

[topspin]

Or you desperately need to tag some system object and the system provides no legitimate means to do so. That can be invaluable when troubleshooting things, or even just understanding how things work when the system fails to document behavior or unreasonably conceals things.

I've been there and done it, and I offer no apologies. The platform preferred and the requirements demanded by The Powers That Be were not my fault.

[gzread]

Ask the Zig people, who just started relying on undocumented unstable Windows behaviour intentionally due to some kind of religious belief: https://codeberg.org/ziglang/zig/issues/31131