131–140 of 158 posts
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And then you had Romero saying that Quake wasn't ambitious enough ...
That's the difference between an engine and game developer.
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DPMI clients don’t run in a VM, though. They’re just a normal task like any other task / process in Windows.
VM in this usage means Virtual Memory - i.e. with page tables enabled. Two "processes" can use the same memory addresses and they will point to different physical memory. In Real Address mode every program has to use different memory addresses. The VM86 mode lets you to have several Real Mode programs running, but using Virtual Memory.
For things like Windows 3.x, 9x, OS/2, CWSDPMI, DOS/4G (DPMI & VCPI), Paging & Virtual Memory was an optional feature. In fact, CWSDPMI/djgpp programs had flags (using `CWSDPR0` or `CWSDPMI -s-` or programmatic calls) to disable Paging & Virtual Memory. Also, djgpp’s first DPMI server (a DOS extender called `go32`) didn’t support Virtual Memory either but could sub-execute Real Mode DOS programs in VM86 mode.
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Amen to that! I think I remember there was some communication between ID and Charles Sandmann about CWSDPMI, so even though it's worded a bit strange for an open source project there's probably some thruth in it? Also a bit strange how the author is surprised about Quake running in a 'VM', apparently they don't really know about VM86 mode in x86 processors...
DPMI clients don’t run in a VM, though. They’re just a normal task like any other task / process in Windows.
Random drive-by nitpick: > From the beginning of the development, id had requested from djgpp engineers that their DPMI client would be able to run on djgpp's DPMI server but also Windows 95 DPMI server. I'm pretty sure that "DJGPP engineers" is just one guy, DJ Delorie. DJGPP was always open source so I bet he got some contributors, but if the rest of this sentence is true that "id has requested from djgpp engineers…
Back then, DJGPP was a much bigger group, and most of the Quake kudos go to Charles Sandmann, author of cwsdpmi, who worked directly with Id to help them optimize their code for our environment.
And here you are!!
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VM in this usage means Virtual Memory - i.e. with page tables enabled. Two "processes" can use the same memory addresses and they will point to different physical memory. In Real Address mode every program has to use different memory addresses. The VM86 mode lets you to have several Real Mode programs running, but using Virtual Memory.
VM does not mean Virtual Memory in this context. VM does mean Virtual Machine. When an OS/DPMI Server/Supervisor/Monitor provides an OS or program a virtual interface to HW interrupts, IO ports, SW interrupts, we say that OS or program is being executed in a Virtual Machine. For things like Windows 3.x, 9x, OS/2, CWSDPMI, DOS/4G (DPMI & VCPI), Paging & Virtual Memory was an optional feature. In fact, CWSDPMI/djgpp pr…
I do dispute your assertion that virtual memory was "disabled". It isn't possible to use V86 mode (what the Intel Docs called it) without having a TSS, GDT, LDT and IDT set up. Being in protected mode is required. Mappings of virtual to real memory have to be present. Switching in and out of V86 mode happens from protected mode. Something has to manage the mappings or have set it up.
Intel's use of "virtual" for V86 mode was cursory - it could fail to work for actual 8086 code. This impacted Digital Research. And I admit my experiences are mostly from that side of the OS isle.
I did go back and re-read some of [0] to refresh some of my memory bitrot.
[0] https://www.ardent-tool.com/CPU/docs/Intel/386/manuals/23098...
When a DOS VM is in windowed mode, Windows must intercept VGA port I/O and video framebuffer RAM access to a shadow framebuffer and scale/bitblt it to display in its hosted window.
In full screen, exclusive VGA access is possible so it doesn't need to do anything special except restore state on task switching.
Quake would be even faster if it didn't have to support DPMI/Windows and ran in "unreal mode" with virtual memory and I/O port protections disabled.
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Back then, DJGPP was a much bigger group, and most of the Quake kudos go to Charles Sandmann, author of cwsdpmi, who worked directly with Id to help them optimize their code for our environment.
Just passing by to thank you. As many others have mentioned, DJGPP was pivotal for my life. I compiled my first C/Allegro games in DJGPP back in the mid/late 90s. And here you are!!
I learned to solder as a pre-teen so I could make a nullmodem :) Then I learned that resistors were a thing when I made a parallel port sound card (this thing https://en.wikipedia.org/wiki/Covox_Speech_Thing ). Fun times!
There wasn't one kind of null modem cable, per se, there were serial and parallel null modem cables.
Originally, there were null modem (serial) adapters that worked with straight through cables but that got expensive, awkward, and complicated. A universal serial null modem cable had a pair of "DB-9" DE-9 female and DB-25 female connectors on both ends so it would work with either system having either type of connector.
A parallel null modem cable had DB-25 male connectors on both ends.
http://www.nullmodem.com/LapLink.htm
Both were used with LapLink and often interchangeably called "LapLink cables" too because the boxed version of LapLink included both cables.
It's amusing to me that in the 90s you could easily play Quake or Doom with your friends by calling their phone number over the modem whereas now setting up any sort of multiplayer essentially requires a server unless you use some very user-unfriendly NAT busting.