Win16 Memory Management

I've been recently working with Classic Mac OS programming[0] and just that memory model (also using dealing with the lack of virtual memory using opaque handles to memory that need to be locked when used) is painful enough[1] - having to deal with segment addressing on top of that does not sound like fun. Thank god for the Motorola 68000!

[0]Made an AppleTalk chat client/server https://github.com/kalleboo/GlobalTalk-Chat

[1]The equivalent to HeapWalker I used was Metroweks ZoneRanger which was bundled with their compiler. It has a nice visualization of how fragmented the memory is https://bitbang.social/@kalleboo/116302075194704555

In 1994 I was 2 years out of school. I'd written one windows shareware application and a whole lot of unix-y things. People were excited about the internet but most people didn't have access. Unix shell accounts via dialup were common though.

One day I was encouraged to write a Windows Sockets emulation layer for ordinary dial-up shell accounts like those offered by netcom. The idea was to allow the use of the recently released Mosaic browser without an actual internet connection. I figured sure, no problem. I'll use curl or some other tool in the shell account to do the actual fetching of URLs, transfer styles over zmodem, and simulate all the tcp/ip calls in the DLL.

I couldn't even get started. The reason is that I couldn't understand how the different Windows applications could all share memory allocated at runtime in the winsock.dll.

I asked a highly experienced ex Microsoft person, and he just said what are you talking about. There's no API to allocate shared memory.

So I gave up. 6 months later someone else did it.

Around then I realized the truth: Windows 3.1 had no memory protection at all. Specifically all global variables in DLLs were shared by default. The hard part wasn't sharing memory among users of a DLL. If anything, the hard part was having good discipline to avoid sharing it.

Since I'd only used multiuser Unix in school, and I knew Windows supported multitasking (even if only the cooperative kind), I just couldn't wrap my head around the idea that I'm multitasking operating system could exist without memory protection.

Pretty good detail in this article! But what really surprises me is how some ideas just keep coming back.

When I wrote a binary translator, I ended up having to keep a translated return stack to optimize RET opcodes. That put me in exactly the same position as the Win16 kernel with regard to having to patch pointers (in case of Win16, just the segment part) on stack.

Of course I did not have the benefit of my guests calling a lock function, so I ended up having to run a garbage collection operation to determine which pointers are in use & take exceptions on now-invalidated segments. Lots of extra work that Windows didn't need: it's nice to be king :-)

If you think programming in Win16 (or whatever we want to call it), you should try teaching people to do it. I worked as a commercial trainer on C and Windows way back when - C and the Windows API were no bed of roses, but the different memory models were mind-numbing for us tutors and the poor punters, many of whom didn't know C!

Sometimes I think that if it were the old days, I probably wouldn't have been able to program. I remember that these days we program on top of 64bit virtual addresses, but how did developers do it back then

> Exports are used for application code which is externally called.

This was the magic moment for me, learning Windows 3.0 programming. The idea that my program is no longer master of it's world, but instead is just something that gets loaded and called by Windows.

Thank god for the 386.

I posted the same thing a few days ago:

https://news.ycombinator.com/item?id=48424862

I'll just stop posting on HN.

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