All kidding aside, this is a great insight into how memory is organised in MS-DOS. As far as I remember having all network drivers in HMA backfired, removing XMS to just below required amount of DOOM. But Extenders like DOS/16M[0] did this transparently fast by having a real-mode process handle DOS interactions. #1. Trust me, it wasn’t a conscious decision, they simply didn’t understand the difference. Most PCs being sold in the very early 90s were still 16-bit; 386 PCs still cost thousands of pounds then. There is a single GDT shared by all code on the system. Even if you never wanted to go back to real mode, the 80286 was brain dead because of the way they laid out the bits in selectors. > On a 286 you do not have access to real mode when in protected mode. 2-player Lemmings or Settlers). I never understood my friends who traded this simplicity for some svga graphics. Thankfully, I’m a little too young to have experienced that… though it was also partly that BASIC was all I had learning materials for, so my father’s Microsoft C/C++ 7.0 and Windows 3.1 SDK floppies and reference manuals were cool but effectively useless toys and what I pined for was QuickBasic 4.5’s compiler. AT compatibles generally included that behavior in their keyboard controllers for compatibility. A crazy trick that did work is to cause a triple fault in protected mode. Also the Amiga 3000 released in 1990 was considered to the best overall computer of its time. The documentation I read at the time claimed that this was to make sharing pieces of segments easier (or perhaps they wanted to encourage people to make zillions of very small segments, e.g., one per procedure). I remember when I discovered that microsoft memory manager was not the only solution. That's where IBM positioned the 5150 it in the market in 1981. It was not 100% PC compatible, but PC business apps often needed only a few small patches to work on the 2000, so official and unofficial ports were available. What in the hell about this post got it downvoted? An Amiga 500 was around $600. Let's look at this from the point of view of a user mode C program running on a protected mode operating system. And even then, the Amiga would still beat the pc in some areas. All kidding aside, this is a great insight into how memory is organised in MS-DOS. You need a 386 for that. A couple of months ago, I actually looked at some code I write in the mid 90’s. Largest executable program size 640,288 (625K) Largest free upper memory block 31,776 (31K) Available space in High Memory Area 15,920 (16K) MS-DOS is resident in the high memory area. A must for anyone who ran a different config for different scenarios. If the paragraph size had been 256 bits (just shift another four bits) then the x86 would have had a logical address space of 16MB, just like the 68K at the time. (edit: $700) A Sun 3 color workstation could easily be $20,000 or more. It was not untill Os/2 that the PC got a real operating system. (-: This, combined with doing the IRQ ISA slot shuffle makes me very glad for modern PC architecture and OSes. Windows 95 was still an extender started from DOS and using its file access subsystem. Memmaker was a godsent little program that MS released with those last versions of real MS-Dos. Microsoft Word) was unstable enough to, from time to time, crash even on NT. The point of this comparison is precisely to tell that despite being theoretically far more powerful than an Amiga 500, PC in the 90s where crippled by all the legacy baggage. I don't think DOS/16M contradicts anything said there. At the beginning of the ’90s, the PC platform was often mocked by its rivals. Those were the days...I remember getting a brand new game, loading it and getting "You need at least 587 KiB of conventional memory to run this game". Which is why I find Windows 95 a truly fascinating OS: A window to the future built on DOS. It was between 92 and 94 that both PC’s and Amiga’s were kind of equal. > Then I learned about boot disks. While each 32-bit app gets it's own 'allocated' memory space, they all must share the lower 4 GB of memory because they can't address memory above 4 GB. By 1990 no one cared anymore. An of course, the absence of a chunky mode made the Amiga line irrelevant for FPS in mid-90s. > Windows 95 was still an extender started from DOS and using its file access subsystem. Look to the '020 machines Sun and others were shipping for examples that make it more attractive. The effort that so many went to in order to grab a few K of memory here and there in the DOS world to get some game to load or to otherwise cram something into a limited address space. In fact, back then a lot of people still used monochrome displays. And it helped that menuitem was a feature as well. The Legend teaches us that Bill Gates once declared that “640 KB ought to be enough for anybody”, then designed MS-DOS to enforce this limitation. And there were lots of 8086-based PCs still being sold in the early 90s, and indeed new models released (e.g. However, in order to keep the "DOS box" working and make sure DOS knew about all the changes to the file system, Windows 95 had to update the DOS structures in memory. I still have near, far, huge pointers and all their variants burnt into my memory! On top of that DOS games came with their own sound drivers and there were only two options adlib and sound blaster pro (again IIRC). Pinball fantasies, dreams and illusions were still better on the Amiga. It wasn't until the mid-80's and the mess that was 286 protected mode[1] that people started to sour on it. Added 640×480 in 256, 64k then 16m colors. I’m the author of this article and also à daily reader of osnews. The default was to launch Windows 95 (from autoexec.bat?) There were a couple ways to do this. Strange comparing an Amiga 500 from the 80s to early 90s PCs, probably “cutting edge” upgraded. Maybe among those who haven’t heard of Next machines? And Watcom C was available from the middle 1980s, too. So I taught myself C using nothing but the K&R book. > None of these segmented memory issues and 640K or 16M limitations existed on that superior processor of the day. None of these segmented memory issues and 640K or 16M limitations existed on that superior processor of the day. > A solution might have been to switch back and forth from Protected Mode. What use is any of this these days? Definitely something to bookmark to share with people who didn’t grow up with this stuff. The more stable Word versions appeared only after the famous Gates' 2002 memo started to be applied to the Microsoft Office products: https://en.wikipedia.org/wiki/Trustworthy_computing#Microsof... Windows 95 was for a time a good trade-off for many practical uses. "It is now safe to turn off your computer". The Amiga 500 was an entry level home computer. It certainly targetted the 32-bit ones, and others besides. I guess the passage of time of made people inquisitive about it. Similarly I once blew away the partition table and had to manually reconstruct it with the only available tool, MSDOS debug.com and a copy of Peter Norton's book. The point of this post was not to say otherwise. I’m pretty sure they didn’t mean to do it. But xe is nonetheless right that DOS/4GW was part of Watcom C/C++. Bill Gates, who understood very early all the implications, is said to have called the 286 a “brain dead chip” for that reason. What did I change... Then I learned about boot disks. Good post, but believe me, you can write a post without ending every paragraph with an exclamation mark. None, that's what. There was a large deployment for a branch of the US armed forces using the product. So we had to tweak. How bizarre. If T is 0, it uses a table called the Global Descriptor Table (GDT). But still once everything was set up, there was nothing like fragging friends over and over again in E1M1. But entering Protected Mode on the 286 is a one way ticket: if you want to switch back to Real Mode you have to reset the CPU! Check the autoexec.bat and config.sys for anything I didn't need. It was a really exciting and special time period from 1990 to 1994. If they are C++ programers, I hope they consider passing it by reference.

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