Win16 Memory Management

6/7/2026 at 12:32:11 PM

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

by kalleboo

6/7/2026 at 1:12:48 PM

It wasn't really the processor architecture. Segmented addressing was actually fairly easy if the processor was used only in the way that protected mode was envisioned as working. As the headlined article observes, a lot of this stuff simply wasn't necessary in OS/2 1.x, even though that too had DLLs, callback window procedures, and the multiple tiny/small/medium/large/compact/huge memory models.

The differences were (a) that DOS+Windows was designed so that the same programs could run in both real mode, with overlaying, and 286 protected mode, with segmented virtual memory; and (b) that to really save on RAM DOS+Windows had ideas such as the data segments for DLLs being globally shared across all processes. These added all of the complications mentioned in the headlined article and more besides. It was the operating system, not the processor architecture.

by JdeBP

6/7/2026 at 1:34:45 PM

I understood it as Windows developers had to manually deal with segment limitations since Windows supported running on pre-286 CPUs without protected mode (Wikipedia says Windows 1-3 all supported the 8088). OS/2 just made the 286 a minimum requirement so they could rely on a CPU with more modern features.

The 68k didn't come with an MMU like the 286 so MacOS couldn't rely on virtual memory like OS/2 did but at least the flat memory space meant you didn't have to juggle 64k segments

by kalleboo

6/7/2026 at 5:30:43 PM

But like real-mode Windows, the Macintosh OS was designed with small amounts of RAM. 32K limits pop up in various APIs. Handle memory allocation.

Not as much of a strait jacket as Windows segmented-memory programming, but compared to Unix, it did feel constricting.

by canucker2016

6/7/2026 at 1:49:52 PM

Yes, outwith the idea of Family API programs (which couldn't use Presentation Manager and whatnot anyway) OS/2 1.x did target the 286 as a minimum. But that doesn't mean that DOS+Windows didn't use the features.

It did. It was bi-modal. There were at one point switches to the WIN command to tell it whether to come up in real mode or 286 protected mode. In the latter it definitely did use the features of protected mode.

It was the bi-modal nature that was the problem. Essentially, they had to design a whole layer that simulated when in real mode all of the load-on-demand stuff that the processor architecture supplied for free in 286 protected mode, and make it so that the thing would all work either way with no changes to applications.

by JdeBP

6/7/2026 at 3:51:50 PM

> There were at one point switches to the WIN command to tell it whether to come up in real mode or 286 protected mode. In the latter it definitely did use the features of protected mode.

Windows 3.0’s WIN.COM supported:

/R for real mode (8086)

/S for standard mode (16-bit protected mode)

/E for 386 Enhanced Mode (32-bit virtual machine manager (VMM), running Windows in VM1, and DOS apps in VM2+)

by skissane

6/8/2026 at 7:41:22 PM

I actually found programming on the Mac a lot more painful due to the +/-32K max displacement for BRA/BSR, in MPW you had to manually shuffle blocks of code around to get them into the 32K jump range while in Windows the tools took care of it for you.

by pseudohadamard

6/9/2026 at 5:55:43 AM

Early editions of Inside Macintosh implied that code segments couldn't exceed 32 KB, so you'd never run into that situation. (It's not clear whether this was an enforced limitation or just a recommendation.) Instead, developers were expected to divide their applications into multiple CODE segments, using jump table entries in the A5 world to branch between segments.

Later in the operating system's lifecycle, applications typically used a single code segment and a custom loader to apply relocations, allowing them to use JSR within that segment.

by duskwuff

6/7/2026 at 9:25:16 PM

Windows never had a global name space for dynamic symbol resolution.

IMHO one of the best design decisions they made; the Unix dynamic linking model seems absolutely like an absurd workaround in comparison.

Also, no mention of FixDS? https://www.geary.com/fixds.html

by userbinator

6/8/2026 at 8:36:01 AM

Not all UNIXes, Aix dynamic link model is XCOFF and quite similar to Windows.

by pjmlp

6/8/2026 at 6:27:51 AM

> the Unix dynamic linking model

What? It's just like static linking! Only, you know, we do it at load time. At least the filenames of the shared objects to load are included into the executable — we could instead just load and search the whole of /usr/lib in unspecified order, you know!

by Joker_vD

6/7/2026 at 9:43:46 AM

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

by jdw64

6/7/2026 at 8:02:43 PM

I think programming often was easier back then. You didn’t have to know about 120 AWS services or security issues. The world was pretty small and you could mostly understand all details of the system you worked on. But it was more tedious for sure.

by vjvjvjvjghv

6/8/2026 at 3:30:15 PM

It was. I learned so much by reading books and computer magazines. Now we have layers of layers of cruft to wade through.

by icedchai

6/7/2026 at 12:33:27 PM

As someone who grew up coding after it was mostly 32-bit, I can't say this with certainty, but my gut feeling is that paradoxically you would have and it would've made you stronger.

by jchw

6/7/2026 at 2:45:07 PM

I think it'd be mixed.

I think the knowledge of underlying hardware is useful and good to know.

But also that sort of knowledge got dated pretty quickly in the early computer era. Further, the capabilities of things like optimizing compilers quickly got to a point where they'd outpace most hand written assembly. Today, it's basically just floating point operations where you can still do better than a compiler.

In the early days, you'd have the correct impression that the C compilers spat out utter garbage which was a lot slower than what you could hand craft. As optimization techniques got better and better, the work you did because the compiler was dumb ultimately would have gotten in the way.

by cogman10

6/7/2026 at 12:59:09 PM

Exactly. I'd argue that all those programming Gods and Gods because they went through that period. Whatever didn't kill them made them stronger. We should replicate that experience by deliberately writing in low level C and assembly for a few years.

by hnthrowaway0315

6/7/2026 at 10:09:02 PM

>"by deliberately writing in low level C and assembly for a few years"

Ha. kid's stuff. I started with punching machine codes straight into memory

by FpUser

6/7/2026 at 10:09:48 AM

Attention spans were longer.

by kev009

6/7/2026 at 10:48:48 AM

I've been wondering about this lately. As a kid, I spent hour upon hour learning about computing: typing in Basic code from a magazine into a Commodore 64, playing with music on an Atari STe, learning my way around a DOS command line, dabbling with 3D modelling... just so much stuff that my own kids would never have the patience for.

I wonder if it's just that kids today (gods that makes me sound old!) are constantly surrounded by entertaining things to do - gaming, TV/films, music, social media.

by GordonS

6/7/2026 at 10:55:41 AM

I think that's actually a pretty accurate observation. I'm not a cognitive science expert, so I don't know the details, but there have been articles about 'popcorn brain' due to sustained attention issues, right? Personally, I use LLMs for coding quite often (in my environment, I'm often forced to use them). Compared to the past, when I use an LLM, the answers come immediately, so it seems harder to focus deeply than before. The generation younger than me, which is more focused on Shorts, probably has it even worse

by jdw64

6/7/2026 at 11:25:01 AM

I think it's an adaptation. Instead of living in a world with limited valuable information we're now living at the end of a firehose of never-ending near-useless information which has to be filtered at high speed.

by trumpdong

6/7/2026 at 10:52:01 AM

Thats correct - and I notice that on myself. There are just much more things reachable at any point in time compared to our youth it takes real effort to focus.

by Braini

6/7/2026 at 1:12:18 PM

I have been shielding my 6 years old son from electronics, except 40 minutes of TV twice a week. I have no idea how to grow his patience and perseverance, though. He is like me, who doesn't have a lot of patience to begin with, so I can't really guide him through some of the situations. We have been taking him to some activities as well as reading to him but nothing really sticks.

I just hope eventually he loves reading and learns in a more traditional way instead of from laptops and pads.

by hnthrowaway0315

6/7/2026 at 1:18:16 PM

We struggled to get our son into reading too, but he took straight away to comics, and from there he had a long stint with graphic novels (e.g. Percy Jackson, Artemis Fowl). You can get more mature graphic novels as they mature and progress, e.g. City of Dragons. And eventually he picked up an Alex Rider book, and hasn't stopped since. He's now how I remember myself as a kid - nose stuck in a book, completely engrossed!

by GordonS

6/7/2026 at 6:43:27 PM

6 is pretty early to enjoy reading books, so I wouldn't worry.

by the-smug-one

6/7/2026 at 1:05:41 PM

I have been wondering how to train my 6-year old son and myself to increase my attention span.

Some rules are obvious -- cutoff mobiles and pads completely (he doesn't have access to them so it's for me), sit in the library and study from books (I believe this is even possible for programming topics as I can write on paper). Basically, cutting off everything electronics definitely helps -- even putting my phone in the bag improves productivity significantly.

But the problem is, my son is unruly. If I put him in the library, most likely he runs around and messes things up, which ends up we leave early without doing anything.

by hnthrowaway0315

6/7/2026 at 3:48:48 PM

> But the problem is, my son is unruly. If I put him in the library, most likely he runs around and messes things up, which ends up we leave early without doing anything.

Some potential ideas to explore. Take what you want, leave what you don't.

a) if you're training for attention span, make sure the target is appropriate and also within reach of your child.

b) have a plan for the visit: when I helped at a school library, classes for kids in your kid's age group would come in, the librarian would read them a story, then the kids would look for a book, check out at the desk and read (or look at the book anyway) quietly until the end of the visit. I think we'd get about 40 minutes for a visit. Most days, at least some of the kids would be getting ansy before it was time to go.

c) Plan around your kid's activity needs. Some kids will do long still antention tasks better after doing some amount of physical activity. Some kids will do these kinds of things better after a meal. Some will do it better in the morning or the afternoon. Many kids will have a harder time if the library visit was a surprise. You know your kid, try to have your library visits when they're likely to work well. If he likes story time, try to visit when there's a story time available.

d) don't expect that you can both go to the library and work independently. You're going to the library with him, and he's going to need you to help him out for much of the time. But you might be able to find him a book together, then find you a book together, then sit down and read for a bit together.

e) if all you can get done is finding a book, no big deal. You can read at home too.

If a lion can figure out how to behave in the library, so can your kid ;) https://www.michelleknudsen.com/library_lion_77788.htm

by toast0

6/7/2026 at 3:24:10 PM

It's easy when it's the only way to get things done. Think about how nobody who was learning programming before 2023 was seriously thinking "This would be so much easier if the computer wrote it all for me".

by unleaded

6/7/2026 at 12:03:44 PM

16-bit x86 processors took 20-bit pointers, expressed as a 16-bit segment and a 16-bit offset. The segment was shifted four bits left and then the offset added. Which means there are lots of different segment:offset pointers that point to the same address. Segments are loaded into a segment register (one of CS, DS, ES, or SS) and then combined with an offset pointer in another register to create a pointer in this way. For example, 1e37:0008 would become 1e378.

It's complicated and janky as all get-out, but it made more sense if you were coming from 8080/Z80 development, as this was a scheme to ensure some degree of compatibility with 16-bit 8080 addressing while providing access to much more memory. 8086 was not binary compatible with 8080, but was designed so that 8080 programs could be machine converted to 8086 ones.

In languages like C, this took the form of three different types of pointers: NEAR, FAR, and HUGE. NEAR pointers were 16-bit offsets only, and dereferenced with respect to the current segment (usually in DS). FAR pointers were full segment:offset pairs but pointer arithmetic was only done on the offset which meant objects could be 64K max. HUGE pointers allowed for objects larger than 64k but at a significant performance cost.

by bitwize

6/7/2026 at 10:32:32 AM

16 bit programs used 16 bit addresses, generally speaking.

Even with 32bit systems where you’d want more than 4GB RAM, application software still had 32 bit addresses (and thus 4GB memory limit).

I think it was a lot more common for 8bit systems to allow for 16 bit addressing though.

It’s been a while though. So hopefully I’m not misremembering things.

by hnlmorg

6/7/2026 at 11:11:51 AM

You had to deal with two flavors of pointer, near and far. Far pointers came with segment selector, for accessing more than 64k. Your choice of memory model influenced the defaults. You might use near pointers for internal references in a module, and far pointers for external references.

by barrkel

6/7/2026 at 11:27:05 AM

I guess it was awkward to use languages that had higher level than assembly in order to write 16-bit programs that required more than 64KiB of memory. And also not quite portable, since they were all tied to x86 CPU. Those were messy times I guess. A somewhat similar story was 32-bit PAE, where the the CPU could address more than 4GiB physical memory, but software was still 32-bit and virtual addresses were capped at 4GiB. Linus was right that you must have more virtual memory (preferably 10+ times more) than physical, otherwise you have to jump through hoops. https://cl4ssic4l.wordpress.com/2011/05/24/linus-torvalds-ab...

by senfiaj

6/7/2026 at 4:50:49 PM

"portable" used to mean "able to be ported" rather than the "comes automatically ported if you just change compiler options" that it means today

by trumpdong

6/7/2026 at 9:05:09 PM

All software is portable by that former definition.

When people talked about portable before, they meant code that used an abstraction that was platform agnostic. And that’s how it’s still used today. It’s just we have better abstractions now so our expectations of what is “portable” have gotten stricter.

Eg the P in POSIX (which is nearly 40 years old now) is “portable”. The point of POSIX was to provide common abstractions that one could build against to run on multiple different operating systems. It wasn’t about porting software, it was about preventing people from needing to constantly write platform-specific ports.

by hnlmorg

6/7/2026 at 10:46:12 PM

It was about making software easier to port. You still couldn't necessarily just write software for all operating systems at once, but you had less porting work because less stuff was different because of the standardisation. So open(argv[1], O_RDONLY) works on all POSIX systems, but if you want to create a pseudoterminal, it's different on each, and if you want to create a container, they don't even use the same concepts.

by trumpdong

6/7/2026 at 10:57:09 PM

> but if you want to create a pseudoterminal, it's different on each

This is somewhat outdated information. POSIX.1-2001 added "posix_openpt" to create a pseudoterminal, and most POSIX implementations now support it–at least Linux, macOS, FreeBSD, NetBSD, OpenBSD, Solaris, z/OS, AIX, HP-UX, QNX, Minix and Cygwin do. (Of course, that's only true of current versions, if you go back a decade or more you'll find many of them hadn't implemented it yet.)

by skissane

6/8/2026 at 7:47:46 AM

But you’re now arguing the same point I am: Portable means low effort porting.

Saying something “can” be ported doesn’t make it portable. People would port games from the NES to the Master System, to 8 bit Micros but in most cases they were effectively complete rewrites because there wasn’t any common abstractions between those platforms.

Where as tools like POSIX provided abstractions to make code portable.

As I said before, the only reason you think the term has changed over the years is because the abstractions have gotten better and thus people’s expectations for how much effort should be required to port have gotten stricter. But that doesn’t mean the term means something totally new.

And by the way, I have authored portable terminal emulators and $SHELLs. ;)

by hnlmorg

6/7/2026 at 12:15:06 PM

> I think it was a lot more common for 8bit systems to allow for 16 bit addressing though.

The 6502 and Z80 could use 16 bit addressing to access up to 64kb of memory. The 6502 had various other addressing systems, including iirc 8 bits, but none of them were wider tha 16 bits.

by andyjohnson0

6/7/2026 at 10:49:48 PM

> The 6502 and Z80 could use 16 bit addressing to access up to 64kb of memory. The 6502 had various other addressing systems, including iirc 8 bits, but none of them were wider tha 16 bits.

Many 6502 and Z80 systems used bank switching to support more than 64KB of memory. That way you could have 128KB or more physical RAM in a machine with an only 16-bit address bus. MP/M–the multitasking/multiuser version of CP/M–had support for this as a standard feature, since it was hard to fit multiple processes/users into only 64KB; it was ported to the single-user/single-tasking version in CP/M 3.0

Essentially, this was doing virtual memory, not inside the CPU, but in one or more external chips. Actually, back in the 70s and 80s, it wasn't uncommon for a memory management unit (MMU) to be a separate chip (or even PCB) rather than an integrated part of the CPU–for many systems it was an optional add-on if you needed more memory, or wanted to run more advanced operating systems.

by skissane

6/7/2026 at 1:11:08 PM

Oh yeah. I had loads of 6502 and Z80 systems (still do in fact). Can’t believe I forgot about that!

Though in fairness, I do mostly now just use those systems to teach my kids BASIC

by hnlmorg

6/7/2026 at 3:41:05 PM

Just curious how do you teach kids BASIC. I’m sure my 6 year old won’t sit tight.

by markus_zhang

6/7/2026 at 8:57:29 PM

I usually start with game: guess the number.

The computer generates a random number between 1 and 100. And you have to guess. When you’re too high, the computer says “too high” and likewise when you’re too low.

It’s a great starter program because it teaches you strings (the output printed), integers, comparisons, conditionals, and iteration (you keep guessing until you get it right). And the whole thing only take around 20 lines (give or take).

Then the kids plays a few games of that.

And after the novelty of that game wears off, I tell them to customise it however they want. Eg different messages, different ranges to guess from, etc.

It’s the same way I teach Python to primary school / kindergarten kids.

The nice things about this is even if the kids don’t learn and remember the basic primitives, they still get a feel of “proper” coding in the same way that we did when we grew up. And they still get something they can play, even if the game itself is super basic (no pun intended).

I’m not saying this will work with every child, though. All kids are different. But it’s been super successful both at home and in the schools I’ve helped out at.

by hnlmorg

6/8/2026 at 1:08:35 AM

Thanks! This is a good idea. I was thinking about typing games and such because he needs to learn words before doing anything useful, but guessing games are definitely fun, too. I can definitely write simple games using QBASIC (was preparing a Dospian on Rpi 4 as his 6 years old birthday gift).

Do you have any blog, or any recommendation of books to read for such topics? Maybe I can find some "Programming for kids" book back from the 90s. I find teaching kids in general very hard, much harder than teaching myself because kids don't have the cognitive capacity as an adult.

by markus_zhang

6/8/2026 at 3:31:20 AM

My parents got me this QBASIC book when I was in elementary school and I remember it being pretty accessible even for very young readers.

https://www.abebooks.com/Absolute-Beginners-Guide-Qbasic-Per...

Also the Usborne series are classics and a lot of them have been made freely available:

https://usborne.com/us/books/computer-and-coding-books

by vunderba

6/9/2026 at 3:19:30 AM

Thank you! That's an expensive book. And looks like all QBASIC books are like that because they were rare to find anyway.

Maybe I'll just leverage my programming experience and build something using online tutorials and a Dosbian box.

by markus_zhang

6/9/2026 at 3:21:38 AM

Haha yeah that's a pretty stupid price. You can get it on eBay for $12 but you'd better bid fast because I'm sure it's going to be a very competitive auction. :)

https://ebay.io/m/zzT1Xf

by vunderba

6/8/2026 at 7:53:56 AM

To be honest I just picked moments when the kids were bored and wanted daddy time but weren’t buzzing around the house with excess energy to burn.

It wasn’t something I specifically planned in advance for. Which meant though whole experience was less like homework for them.

As I’m sure you know, sometimes kids just want to experience the stuff their parents do. And when they’re in that kind of mood it’s a lot easier to sit that at a computer than it would be normally.

by hnlmorg

6/9/2026 at 3:18:06 AM

Thanks. I think I'll prepare that Dospian box, learn QBASIC myself quickly, and let him try it out gradually. At least he should get some typing and arithmetic "game" experience, even when he is too young for any programming.

by markus_zhang

6/7/2026 at 1:30:52 PM

Well, most of the addressing modes of the Z80 used a 16-bit register pair (i.e. 0 to 64K-1 bytes) to address, the 6502 used a somewhat stranger set of addressing modes, but once again you could address 0 to 64K-1 bytes.

by zabzonk

6/7/2026 at 12:24:47 PM

Psst! Let's blow their minds and tell them about the MC68008. (-:

by JdeBP

6/7/2026 at 2:43:51 PM

And the 32-bit 4GB limit was often really "just a bit under 2GB" depending on the hardware, OS, etc

by bluedino

6/7/2026 at 4:39:36 PM

3/1 split was common, though. Especially towards the end of 32-bit era.

by vardump

6/7/2026 at 12:43:56 PM

Not really. 16-bit programs on x86 used 32-bit pointers (effectively 20-bit due to the segment mechanism).

8-bit microprocessors used 16-bit addresses.

by cyberax

6/7/2026 at 6:01:20 PM

Some of this was automatically handled by the compiler and wouldn't have been an issue. Current x86-64 ABIs, for instance, require function entry to use specific forms annotated by metadata to support stack walking to support exception handling. Like the far entry here, this is invisible to most programmers -- the compiler does it for you.

Similarly, while locking and unlocking memory blocks is no longer generally a concern, most programs still deal with files, and graphics programs still have to call map/unmap functions to access graphics data. All the same tools apply -- helper functions/libraries, RAII, and leak/sanitizer tools to dynamically detect usage errors.

by ack_complete

6/7/2026 at 11:43:37 AM

I first found out about segmenting in 16 bit systems in 2016 by reading a lively explanation from an older edition of Duntemann's Assembly Language Step by Step (the newer editions focus largely on Linux and 32/64-bit systems).

by bananaflag

6/7/2026 at 1:37:52 PM

Memory mapping/bank switching was fairly common on 8-bit and 16-bit systems, where a small memory window was used to select different memory banks, allowing a program to access more memory in chunks.

Game consoles like NES, SNES and Game Boy had additional hardware built in the cartridge to support memory mapping/bank switching.

For PCs, EMS (memory) provided a similar concept. It reserved a 64 kB window divided in 16 kB pages in the first 1 MB and allowed to map up to 32 MB.

by icelusxl

6/7/2026 at 11:05:03 AM

You had to figure out so much on your own back then - and reinvent the wheel.

For me it is fascinating how today I can learn a foreign language, or how to code by interacting with the LLM.

by rvba

6/8/2026 at 2:08:30 AM

I can tell you about my experiences with this, which from what I hear are unusual. I first learned programming in C128 BASIC. Then on the PC it was QBasic and Turbo Pascal, and later Perl.

What all of these languages have in common is that you can write meaningful programs entirely without pointers or manual memory management. In particular, all of these languages handle strings in a natural, high-level way (treating them as a value) and don't require you to allocate and free buffers for them. Perl goes a step further with arrays and hashmaps and employs a full garbage collector.

I have vague memories of trying C for the first time and getting completely lost and bogged down by all the pointers and memory management. My reaction was the same as yours: how does anyone program in this. Why bother with this complexity when you can just use Pascal where you simply don't have to.

Of course, the Pascal compiler was likely written in C or assembly and all the memory management still had to happen even if it was hidden away from me. To some people, this might mean that I “lost” something, but to me, it meant greater freedom as I was able to explore the world of higher-level programming which I found interesting, and not have to bother with the low-level details which I found tedious and even infuriating.

by Timwi

6/8/2026 at 9:41:06 AM

On the contrary, Pascal compilers were usually written Pascal with a bit of assembly where needed :)

by andrewshadura

6/7/2026 at 2:54:56 PM

https://news.ycombinator.com/item?id=48435428

by rramadass

6/7/2026 at 5:40:48 PM

You just had to live with the constraints.

It biased your selection of data structures and algorithms.

Max 64KB array size meant pointers to allocated structs and linked lists were much more popular back then versus 1 large array of structs.

The Win16 HANDLE memory allocation also meant you had to worry about how you handle structs which had pointers to others structs (a FAR ptr may not be a stable value, unless you locked the HANDLE for the duration of the allocation)

Then you had to worry about stuff that no college programming book talked about (ignore the lack of error checking):

  char FAR *p;
  char FAR *mem = farmalloc(65536);

  for (p = &mem[65535]; p >= &mem[0]; p--) {
    dostuff(p);
  }

Welcome to an infinite loop...

by canucker2016

6/7/2026 at 6:13:29 PM

  char FAR *p;
  char FAR *mem = farmalloc(65536);

  for (p = &mem[65535]; p >= &mem[0]; p--) {
    dostuff(p);
  }

Nice one.

To be fair to Windows, good C courses should still teach this, but I'm not sure if they do :-)

It's UB to set a pointer to before the first element of an array, or after the last element plus one. So, if it knows the call to farmalloc/malloc returns the start of an object, a modern C compiler on a modern architecture may, in principle, optimise the above to an infinite loop.

I've seen something similar on architectures (long ago) where a zero-bit-pattern pointer was a valid memory address you might actually access. Of course p-1 is not less than p when p is zero.

by jlokier

6/7/2026 at 6:23:54 PM

None of my college CS courses used programming languages that featured FAR pointers.

The above example would cause an infinite loop on Win16's seg:off far memory model, but compiling on Win32 would not cause an infinite loop.

Problem is that far pointers only affect the offset, not the segment. So decrementing a 0 value offset would just wrap around to 0xFFFF and the segment would stay the same, so you're going from mem[0] to mem[65535] not mem[-1].

by canucker2016

6/8/2026 at 6:35:01 AM

My point is the example code has a generic C bug, not depending on FAR, which is why it should be taught in good C courses.

Although the code worked on Win32, and works on most modern C compilers, it's not guaranteed to work on modern C compilers, especially with aggressive optimisation turned on.

by jlokier

6/8/2026 at 5:48:08 PM

I'm not disputing your point.

I'm explaining why the infinite loop actually occurs for those who haven't encountered the problem.

The problem would happen for an array whose beginning element starts at offset 0 for a particular segment and an iteration stop condition that uses ">= 0th element" that scans down the array. I used a 64K allocated array to ensure that the array base would match offset 0.

Problem would also occur if the end of the array aligns with the segment limit and the iteration end condition was "<= end element" and the scan moves up the array.

For either situation, the array could be < 64KB. One byte would be sufficient.

by canucker2016

6/7/2026 at 11:02:23 AM

I think they learned by reading books such as Undocumented Windows or Windows Internals (not to be confused with Windows NT internals), and Microsoft documents.

In fact, I’d argue it was more fun than programming Javascript these days.

by markus_zhang

6/7/2026 at 12:56:20 PM

It wasn't really the 'Undocumented' and 'Internals' books. Pretty much everything in the headlined article was to be found in the SDK, Microsoft Press publications, and in many third party books about DOS+Windows programming.

Petzold's Programming Windows book, for example, devoted an entire chapter (chapter 7) to memory management, with diagrams and examples. In the 2nd edition (which I just pulled off the shelf to check) that chapter runs to some 40 pages.

by JdeBP

6/7/2026 at 2:08:06 PM

Yeah you are right. I just listed two random books.

by markus_zhang

6/7/2026 at 2:52:22 PM

Good informative article.

Win16 programming was an important formative phase in my career. There is a lot of wisdom in old solutions to thorny problems and knowing them often clues you to how one may adapt them to today's problem. For example, when CPU+GPU programming appeared i immediately imagined CPU memory accessed with "near" pointers and GPU memory accessed with "far" pointers with a switch to a pseudo-segment register.

It also conditioned a programmer to learn about various complexities involved and be careful in their programming i.e. it taught you discipline. You understood your compiler, OS and hardware better and how to write code keeping them all in mind. For example, i often say my study of embedded programming started with Win16!

Another bit of cleverness was "Thunking" between 16-bit and 32-bit code. Here is Raymond Chen on how it worked there and Why can’t you thunk between 32-bit and 64-bit Windows? - https://devblogs.microsoft.com/oldnewthing/20081020-00/?p=20...

by rramadass

6/7/2026 at 1:37:59 PM

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.

by boutell

6/7/2026 at 9:59:08 PM

> Windows 3.1 had no memory protection at all

All of the below is... IIRC

Win16, even in protected mode, in general didn't unless you opted out of the shared VDM. This was to preserve compatibility with how non-protected mode code worked. That said 32bit code or code that specifically marked itself as protected mode got it's own memory space.

> I just couldn't wrap my head around the idea that I'm multitasking operating system could exist without memory protection

NGL... I was shocked when I found out that MacOS before 10... really didn't have much protections at all.

by leeter

6/8/2026 at 8:39:28 AM

Owning reference books like Petzold, already doing C++ and TP coding on Windows 3.x, I am quite sure that the protection was there for Win16 applications in 386 Enhanced mode.

Now in regards to DLLs it all depended on which memory segments were being used, and the respective code on DllMain in regards to the thread/process attachment code and related handles.

Knowing what to search for quickly gave me this article from back in the day,

https://learn.microsoft.com/en-us/archive/msdn-magazine/2000...

by pjmlp