Consider that early PCs were quite explicitly *not* gaming platforms. Tandy tried to correct that with their re-imagining of IBM's PC Jr, but that was very much an outlier, on the PC Jr branch of the PC tree, not the main PC-XT-AT line.

Early PCs were shipped with 128kB RAM, but by 1983 and the XT 512kB was an entry-level configuration. So you can definitely assume more RAM.

On the other had, 8086 CPUs were rare, 4MHz 8088 CPUs (with 8b external bus, quite a bit slower) were the default. Even Turbo XT systems (usually found well after CGA era, either having Hercules or VGA) had a faster 8088, not an 8086. The few 8086 systems (eg. Olivetti M24) performed significantly better, but were as much outliers as the Tandies. So if your software performs poorly on a 4MHz 8086, I'd either reconsider the CGA requirement or thoroughly re-optimize code.

360kB floppies were DS/DD.

That's super interesting to read, thanks!
I think I'm fine then. The "lag" I was talking about is only when printing text which is rare and easily optimizable (e.g. by NOT using software interrupt like I'm doing right now 😜)

I'm a bit surprised to read that Tandy was an outlier. I always assumed that Tandy 1000 was super popular and sold a shit-ton of units by being a cheaper IBM.

1984=

Clean MDA Hercules or Blurry Ass CGA
512 KB RAM
1 × 360 KB floppy
10 MB hard drive
PC-DOS 2.1 ( subdirectories and config.sys were still fairly new things)
Model F 83 key keyboard (no F11, F12 or arrow keys outside the number pad)

As for sound, what comes to mind:
- PC Speaker
- AdLib (obviously)
- Game Blaster (CMS)
- Disney Sound Source (or Covox Speech Thing)
- Covox Sound Master
Edit: List applies to late 80s, my bad.
The MS-DOS compatible Sirius-1/Victor-9000 had PCM sound, though.
https://youtu.be/A93TmmF3Q3w?t=2405

About the RAM.. That's actually funny.
Because were I live, XTs did tend to have full 640KB base memory while ATs had just 512KB (1985/1986 and onwards)!
That's probably because of PC/AT memory boards, which assumed 512KB base memory configuration to expand on.

The exception to this rule were models like the PC1512, which was superseded by the PC1640.
The Amstrad/Schneider PC1512 had and 8086 CPU and 512 KB of RAM (with 640 KB upgradebility on motherboard) and an enhanced CGA chip.

Some XTs and many PC emulators of the 80s even featured 704 KB of RAM.
PC-Ditto for Atari ST, for example. It featured CGA and 703 KB of RAM.

Anyway, you should always assume at least a basic installation of MS-DOS 2.11 or MS-DOS/PC-DOS 3.x too.
It takes away some bit of the conventional memory, too.
Drivers for mouse and keyboard must be taken into account, too.

Here's an incomplete overview:
Conventional Memory consumption of various DOSes

MS-DOS 4 ('88) was rarely used by XT users, because it had higher requirements than DOS 3.3x.
Except were I live, I mean. Commodore PCs were bundled with OEM versions of DOS 4. So XT users did use it here.

Good luck! 🙂

Edit:

- 360K floppy disk (where these double sided?)
- No hard disk present

Does this sound a plausible configuration at some point in time during the 80s?

Hi! Users who didn't have a fixed-disk usually had 2x 360 KB drives.
One drive for DOS system disk, one for application.
Or one drive for DOS+application disk and another one for data.

Users with fixed-disk, one of the two 360KB diskette drives might have been substituted for a 3,5" 720KB drive.
To exchange data with laptops, Atari ST etc.

For serious PC use, a fixed-disk, RAM disk or network drive was required though.
This wasn’t the Amiga or C64, after all. Only the poorest could justify not getting a fixed-disk drive eventually.

Edited.

My first system was a ibm 5150
XT 8088 4.7mhz
640k ram
cga video card
cga monitor
10 megs hdd and then upgraded to 20megs
floppy 5 1/4 360k

XT was popular. 8086 rare. i got a 8086 2 years after the 8088, with 640k too and cga.

renejr902 wrote on 2025-09-14, 04:28:

XT was popular. 8086 rare. i got a 8086 2 years after the 8088, with 640k too and cga.

Well, yes and no. Depends on point of view.

PC and PC/XT clones did follow (the somewhat modest) IBM design closely.

However, serious developers had used the real thing, the 8086.
The STS, the Space Shuttle had used 8086s, for example. ;)

The c't-86 homebrew PC from 1984 used Europa-card boards and an 8086.

S-100 computer cabinets used 8086 cards rather than 8088, I assume.:
The i8080, i8085 and Z80 all were full versions, but the i8088 was cut-down.
http://www.s100computers.com/Hardware%20Index%20Page.htm

The Olivetti M24 (aka AT&T 6300, LogAbax Persona 1600, Xerox 6060) had 8086. And 400 line CGA.
Europe's shortlived bestsellers PC1512 and PC1640 used 8086. Also had enhanced CGA.

Or the Victor Vicki portable of 1984.. Also an 8086, running at 4,77/7,16 MHz.

The problem is that many early 808x computers running DOS had some level of IBM PC compatibility (such as CGA, BIOS interrupts or floppy controller),
but were not IBM PC clones (aka "IBM PC or compatible", "IBM compatible" etc).
They belong in a separate category, the so-called "MS-DOS compatibles".
Because it was Microsoft who licensed DOS to other manufacturers (OEMs).
The DEC Rainbow 100 or Sanyo MBC-550 can be considered examples, maybe.

I really don’t mean to annoy people or try to nitpick.
It's just that the era of CP/M computers running DOS is hardly remembered anymore.

Before the IBM PC became industry standard, it was common to adapt OSes such as CP/M for a specific computer model.
Applications such as WordStar merely needed to be told which terminal type to be used.
For example, VT-52 or VT-100 were simple serial terminals, but with cursor control (via escape sequences).

Edit: Here in Europe, as far as I understand, the IBM PC wasn't available in 1981.
Well, except in low numbers, maybe. IBM wasn't sure about international sale.
Hence it took up until 1983 that the IBM PC was available (in UK first?).
So over here in Europe, it was the Sirius-1 which almost became industry standard/market leader - rather than IBM PC.

Edit: About RAM.. Let's put it this way:
The minimum -in early 80s- to run DOS 2.x reasonably was 256 KB. So that’s our lower bottom.
Many low-end PCs of 1983/1984 did have at least this. 512 KB was being the recommended, though.
By 1985, the full 640 KB wasn't being uncommon.
Applications ran out of memory already, hence the birth of EMS.

Computers with 256 KB of RAM or less either ran IBM's ROM BASIC or MS-DOS 1.25.
Which almost no applications from 1985 onwards do support anymore.
The famous Norton Commander needs MS-DOS 2.x already, for the directory support alone.

Computers stuck to MS-DOS 1.25 often are the MS-DOS compatibles who were abandoned and didn't receive any updates anymore.
Though in some cases, some still got their final boot floppies with MS-DOS 2.x or 3.20 (!).

Edit: My recommendation is to get an cheap 8088 laptop, such as Toshiba T-1000, for testing purposes.
It usually has CGA, no HDD (but RAM disk or second FD drive), runs MS-DOS 2.11 from ROM..
The on-board RAM has 512 KB, as well. Being a laptop, its years behind the current gen and compares to an early desktop PC.

Jo22 wrote on 2025-09-14, 05:44:

Well, yes and no. Depends on point of view. […]
Show full quote

renejr902 wrote on 2025-09-14, 04:28:

XT was popular. 8086 rare. i got a 8086 2 years after the 8088, with 640k too and cga.

Well, yes and no. Depends on point of view.

PC and PC/XT clones did follow (the somewhat modest) IBM design closely.

However, serious developers had used the real thing, the 8086.
The STS, the Space Shuttle had used 8086s, for example. 😉

The c't-86 homebrew PC from 1984 used Europa-card boards and an 8086.

S-100 computer cabinets used 8086 cards rather than 8088, I assume.:
The i8080, i8085 and Z80 all were full versions, but the i8088 was cut-down.
http://www.s100computers.com/Hardware%20Index%20Page.htm

The Olivetti M24 (aka AT&T 6300, LogAbax Persona 1600, Xerox 6060) had 8086. And 400 line CGA.
Europe's shortlived bestsellers PC1512 and PC1640 used 8086. Also had enhanced CGA.

Or the Victor Vicki portable of 1984.. Also an 8086, running at 4,77/7,16 MHz.

The problem is that many early 808x computers running DOS had some level of IBM PC compatibility (such as CGA, BIOS interrupts or floppy controller),
but were not IBM PC clones (aka "IBM PC or compatible", "IBM compatible" etc).
They belong in a separate category, the so-called "MS-DOS compatibles".
Because it was Microsoft who licensed DOS to other manufacturers (OEMs).
The DEC Rainbow 100 or Sanyo MBC-550 can be considered examples, maybe.

I really don’t mean to annoy people or try to nitpick.
It's just that the era of CP/M computers running DOS is hardly remembered anymore.

Before the IBM PC became industry standard, it was common to adapt OSes such as CP/M for a specific computer model.
Applications such as WordStar merely needed to be told which terminal type to be used.
For example, VT-52 or VT-100 were simple serial terminals, but with cursor control (via escape sequences).

Edit: Here in Europe, as far as I understand, the IBM PC wasn't available in 1981.
Well, except in low numbers, maybe. IBM wasn't sure about international sale.
Hence it took up until 1983 that the IBM PC was available (in UK first?).
So over here in Europe, it was the Sirius-1 which almost became industry standard/market leader - rather than IBM PC.

Edit: About RAM.. Let's put it this way:
The minimum -in early 80s- to run DOS 2.x reasonably was 256 KB. So that’s our lower bottom.
Many low-end PCs of 1983/1984 did have at least this. 512 KB was being the recommended, though.
By 1985, the full 640 KB wasn't being uncommon.
Applications ran out of memory already, hence the birth of EMS.

Computers with 256 KB of RAM or less either ran IBM's ROM BASIC or MS-DOS 1.25.
Which almost no applications from 1985 onwards do support anymore.
The famous Norton Commander needs MS-DOS 2.x already, for the directory support alone.

Computers stuck to MS-DOS 1.25 often are the MS-DOS compatibles who were abandoned and didn't receive any updates anymore.
Though in some cases, some still got their final boot floppies with MS-DOS 2.x or 3.20 (!).

Edit: My recommendation is to get an cheap 8088 laptop, such as Toshiba T-1000, for testing purposes.
It usually has CGA, no HDD (but RAM disk or second FD drive), runs MS-DOS 2.11 from ROM..
The on-board RAM has 512 KB, as well. Being a laptop, its years behind the current gen and compares to an early desktop PC.

interesting post thanks, i didnt know a lot of things.

Edit: Does it exist dos games that are really for 8086 and runs slower on 8088 ? To me all games in these times were made for 8088. I'm curious.

Jo22 wrote on 2025-09-14, 05:44:

Well, yes and no. Depends on point of view.

I think it is pretty safe to say that they are rare when dealing with PC compatibles compared to the abundance of 8088 based systems that were built. It was only used by few larger computer manufacturers with inhouse designed motherboards and often had some proprietary shenanigans. Good luck finding a standard PC 8086 MB which could be installed to your standard case, use all standard peripherals and thus could be used for making those XT clones for example. Amstrad by the way had 8086 available through most of their line-up till early 90s, 5086 was the last I think. I had 2086 back in the day for a while.

Most “famous” 8086 systems were probably IBM PS/2 model 30s which are still quite easy to find. But again we are talking about big manufacturer line up here. The reason why it never became more common is probably the cost: motherboard cost is probably close or on par with 286 because of the 16-bit data bus, so it was just not very cost effective option on increasingly competitive market and offered a modest jump in performance over 8088 while still significantly behind 286.

renejr902 wrote on 2025-09-14, 06:38:

interesting post thanks, i didnt know a lot of things.

Edit: Does it exist dos games that are really for 8086 and runs slower on 8088 ? To me all games in these times were made for 8088. I'm curious.

Of course. If you have for example 4.77MHz 8088 and 8MHz 8086, latter runs faster. Latter is most likely also a somewhat faster than 9.54MHz 8088. But there were not games that were specifically made for 8086, CPUs are identical besides the bus unit. Like there are no games today that are made for some specific CPU. You have some minumum requirement and that’s pretty much it.

However, many early PC games and software were written for 4.77MHz PC, because that was pretty much what PCs were. When faster systems were introduced, this kind of software easily ran too fast on these machines, because there was no code in these games that limited frame rate in any way. Hence the turbo button became common, which could be used to set the CPU speed either 4.77MHz or 9.54MHz.

CharlieFoxtrot wrote on 2025-09-14, 07:09:

However, many early PC games and software were written for 4.77MHz PC, because that was pretty much what PCs were. When faster s […]
Show full quote

However, many early PC games and software were written for 4.77MHz PC, because that was pretty much what PCs were.
When faster systems were introduced, this kind of software easily ran too fast on these machines,
because there was no code in these games that limited frame rate in any way.
Hence the turbo button became common, which could be used to set the CPU speed either 4.77MHz or 9.54MHz.

That was considered bad practice, though. And people knew it.
And before 1984/1985, the MS-DOS compatibles still had some marketshare.

But sure, the software publishers in US were submissive torwards IBM and started to exclusively use the IBM PC as a hard reference,
started to do low-level programming without providing a clean fall-back code.

That's how all this mess had started in first place, I'm afraid.
Early DOS computers such as Triump Adler PC16, Sanyo MBC-55x and various others didn't use 4,77 MHz.

Unfortunately (or luckily), the IBM AT debuted soon in 1984 and had a different processor at different speeds (6 and 8 MHz).
By that time, developers should have immediatdly stopped to assume 8088 and 4,77 MHz clock frequency.

About the Turbo button.. It was related to floppy access, too.
And some applications didn't work correctly with higher speeds, either.
A Turbo button doesn't necessarily always focus on providing 4,77 MHz PC/XT speeds, by the way.
The original IBM AT also was sort of a reference.
Later PC systems with Turbo button perhaps rather tried to match speed of a slow AT, rather than exactly matching a PC/XT at 4,77 Mhz.

Edit: That's also interesting, I think. A CGA compatible video board for S-100 platform.
http://www.s100computers.com/Hardware%20Folde … eo/PC-Video.htm

Edit:

Most “famous” 8086 systems were probably IBM PS/2 model 30s which are still quite easy to find. But again we are talking about b […]
Show full quote

Most “famous” 8086 systems were probably IBM PS/2 model 30s which are still quite easy to find.
But again we are talking about big manufacturer line up here.
The reason why it never became more common is probably the cost:
motherboard cost is probably close or on par with 286 because of the 16-bit data bus,
so it was just not very cost effective option on increasingly competitive market
and offered a modest jump in performance over 8088 while still significantly behind 286.

Speaking of the IBM PS/2 Model (8086 version)..
I always wondered why it used an intel 8086, but not an V30. 🤷‍♂️
It would wave made more sense, because both 80286 and V30 do support the updated 8086 instruction set (8086-2 ISA).
For a line that advertises OS/2, it makes little sense to offer an antique 8086 PC.

Was it because IBM only used intel parts? But it didn't do it the 90s anymore, did it?
And why didn't intel license just the V20/V30 design?

The company already did such thing with the advanced graphics chip, the 82720.
The intel 82720 was an NEC μPD7220.
https://en.wikipedia.org/wiki/NEC_%CE%BCPD7220

Jo22 wrote on 2025-09-14, 07:50:

About the Turbo button.. It was related to floppy access, too. And some applications didn't work correctly with higher speeds, e […]
Show full quote

About the Turbo button.. It was related to floppy access, too.
And some applications didn't work correctly with higher speeds, either.
A Turbo button doesn't necessarily always focus on providing 4,77 MHz PC/XT speeds, by the way.
The original IBM AT also was sort of a reference.
Later PC systems with Turbo button perhaps rather tried to match speed of a slow AT, rather than exactly matching a PC/XT at 4,77 Mhz.

Of course, but PC/XTs is what is discussed here and what OP wants to target with the game. There is no point in confusing him/her or complicating things by discussing unrelated things such as what turbo button does on your Pentium box for example.

The point I wanted to make to answer the question is that the problem was often the other way round when dealing with early games: not that it ran too slow on 8088, while 8086 was good, but that it ran too fast on anything faster than 4.77MHz 8088.

CharlieFoxtrot wrote on 2025-09-14, 08:06:

Jo22 wrote on 2025-09-14, 07:50:

About the Turbo button.. It was related to floppy access, too. And some applications didn't work correctly with higher speeds, e […]
Show full quote

About the Turbo button.. It was related to floppy access, too.
And some applications didn't work correctly with higher speeds, either.
A Turbo button doesn't necessarily always focus on providing 4,77 MHz PC/XT speeds, by the way.
The original IBM AT also was sort of a reference.
Later PC systems with Turbo button perhaps rather tried to match speed of a slow AT, rather than exactly matching a PC/XT at 4,77 Mhz.

Of course, but PC/XTs is what is discussed here and what OP wants to target with the game. There is no point in confusing him/her or complicating things by discussing unrelated things such as what turbo button does on your Pentium box for example.

Um, okay. But my point was that PC history wasn't that simple, that there was some diversity.
If it was simple we could ignore things such as Plantronics, Hercules, NEC V20/V30 upgrades, file cards, CP/M-86 and limit ourselves entirely on Intel/Microsoft/IBM.
I mean, sure, there's always sort of a simplified Hollywood version of something.
"First there was darkness, then IBM in its godly wisdom created the IBM PC Model 5150. Then there was light, a blinking cursor in a void.."

Edit: I saw a YT video a few days ago about a Kaypro 4 with an 8088 board @5,3 MHz (RAM was defective, fixed in part 3).
The MS-DOS was v1.25 and the board could hold 128 or 256KB of RAM.
The advertisement was shown in the video, too. Even claims the board to be "IBM PC compatible".
Unfortunately, it was not entirely. Video output was just plain text, no CGA.
Anyway, not sure if its helpful or not. Or on-topic, or not.
https://www.youtube.com/watch?v=nroIdwecx2k

Jo22 wrote on 2025-09-14, 08:28:

Um, okay. But my point was that PC history wasn't that simple, that there was some diversity. If it was simple we could ignore t […]
Show full quote

Um, okay. But my point was that PC history wasn't that simple, that there was some diversity.
If it was simple we could ignore things such as Plantronics, Hercules, NEC V20/V30 upgrades, file cards, CP/M-86 and limit ourselves entirely on Intel/Microsoft/IBM.
I mean, sure, there's always sort of a simplified Hollywood version of something.
"First there was darkness, then IBM in its godly wisdom created the IBM PC Model 5150. Then there was light, a blinking cursor in a void.."

It isn’t, but the premise of this thread is very simple and OP clearly wants to get few basic things right for the game, that is, he is getting the basic limitations for the hardware right. I’d say that even the whole 8086 vs 8088 discussion here is moot and unnecessary, because it was that back in the day also. Systems with ether CPUs (or NEC variants) offered roughly similar levels of performance. If something doesn‘t run well enough on 8088, it won’t change much better on 8086 of roughly the same clock speed.

In this hobby, like many other, people like to easily pretend that things need to be more complicated than they are and you can find “well, ackshually” replies far too often for questions that aren’t very complicated at all. In a case like this, there is no need to dig deeper of the intricacies of x86 history. There are always outliers, oddities and different applications of CPUs, but that doesn’t change the fact that the basic PC/XT system which OP is trying to target was in the end very homogenous bunch of systems when you look at the IBM computers and many clones that sprung around it. What changed during the years when these systems were relevant was the amount of RAM you had installed, graphics adapter used and CPU speed roughly doubled during the time. It also another discussion what kind of systems games targeted at what time. For example, although CGA was largely obsolete by the late 80s, games generally retained CGA modes well into the 90s.

Something like S100 computers are completely irrelevant in this discussion, how interesting subjct it in itself may be.

In this hobby, like many other, people like to easily pretend that things
need to be more complicated than they are and you can find “well, ackshually” replies far too often for questions that aren’t very complicated at all.

I see. But people like me aren’t ChatGPT, either.
So far, I've just wrote down what I know (or think that I know) of something
and assumed that people would silently skip reading the part they don't find useful.

About "well, actually".. I was raised that way. 🤷‍♂️
That there are always exceptions to a rule or pros/cons and that they should be mentioned in any discussion.

Hm. Maybe we should simply say "yes" to the specs in the OPs first posting?
Because I think that there's nothing wrong with it.
Except that a HDD or a second floppy drive is being recommended, maybe.

RAM. To my understanding, MS-DOS 1.25 needs a minimum of 32KB of RAM in the PC because of boot loader adresses.
Also, I believe only a few compilers are available to compile MS-DOS 1.x applications.

A plain MS-DOS 2.11 roughly consumes 40 KB of memory, so it needs at 64KB of RAM at least.
128 KB leaves little memory to applications, thus. 256 KB or more is better.

Is that about correct? 🤷‍♂️ Because I don’t know how to compress all the information even more.

Something like S100 computers are completely irrelevant in this discussion, how interesting subjct it in itself may be.

Um, Tim Paterson wrote 86-DOS on an S-100 system.
DOS was being created on an 8086 system with S-100 bus, rather than on an IBM PC.

https://en.wikipedia.org/wiki/86-DOS

Thanks everyone for the super interesting discussion. I'm learning a lot of things. For the purposes of my game I can basically summarize:

1) I need to make sure the game runs on 8088 rather than 8086 (I just assumed 8088 was the weirdo and 8086 was the standard, it's actually the other way around). This is not a problem.
2) I'll assume 256Kb of memory or more
3) I need to support either 2 360KB floppy drives OR 1 floppy drive + 1 10/20MB hard disk.
4) I need to downgrade the DOS version used. I was assuming MS-DOS 3.11 at least, but need to test with MS-DOS 2.1. Shouldn't be a problem but I need to recheck the software interrupts I use.
5) I'll assume an IBM compatible PC, both for my mental sanity and because I'm relying on BIOS interrupts to read keyboard, change video mode, etc. I also access video memory directly (interlaced CGA) and I don't think that works outside IBM universe. I also downloaded game manuals for some of the old CGA games (like Phantasie) and they pretty much all ask for an IBM compatible PC. (This is also consistent with what I remember from my childhood, where a friend of mine had an Olivetti and couldn't run all the games I could).
6) I didn't think about the keyboard! I was just assuming 102 keys and relying on scancodes to check for arrow pressed. I'll need to make the code work with XT keyboards as well, I guess. It would be nice if you folks could expand a little on that. How many keyboard layouts where there for IBM compatible PCs? (Let's ignore non IBM ones, since I'm just not going to support those).

Also I'm not planning to buy any hardware and mostly rely on 86Box for testing purposes (it's normally good enough, but it does allow for "fantasy" setups as well, which is why I created this thread). Very informative stuff folks, not sure why I waited so much before posting here 😀

Jo22 wrote on 2025-09-14, 09:45:

About "well, actually".. I was raised that way. 🤷‍♂️
That there are always exceptions to a rule or pros/cons and that they should be mentioned in any discussion.

Like I said, this niche hobby isn’t the only one that easily goes this route, but the problem is that it isn’t helpful. I’ve seen it countless times in different contexts that a newcomer comes with a relatively straight forward question, but it all turns down to a circle jerk of oldbies about all the intricancies of the subject. The end result at worst is that proper answer isn’t never given, the whole thing turns to a confusing mess and the one who tried to find relevant information gets frustrated. It is one of the reasons why some hobbies easily get labeled as elitist. But this is enough for this subject from me.

Hm. Maybe we should simply say "yes" to the specs in the OPs first posting? Because I think that there's nothing wrong with it. […]
Show full quote

Hm. Maybe we should simply say "yes" to the specs in the OPs first posting?
Because I think that there's nothing wrong with it.
Except that a HDD or a second floppy drive is being recommended, maybe.

RAM. To my understanding, MS-DOS 1.25 needs a minimum of 32KB of RAM in the PC because of boot loader adresses.
Also, I believe only a few compilers are available to compile MS-DOS 1.x applications.

A plain MS-DOS 2.11 roughly consumes 40 KB of memory, so it needs at 64KB of RAM at least.
128 KB leaves little memory to applications, thus. 256 KB or more is better.

Is that about correct? 🤷‍♂️ Because I don’t know how to compress all the information even more.

Yes, I’d say 256k is the practical minimum, but of course we don’t know what the scope will be in the end. Also, trying to squeeze something to use as little resources as humanly possible is perhaps one of the challenges OP wants. I wouldn’t find anything wrong with having half meg or whole 640k in use. After all, both became relatively common quite early on.

No HDD is another thing that might fit well to making the project challenging. Either squeezing the game and assets to single floppy or then making the game work from several floppies. Again, I don’t find having a HDD conflicting and it certainly would give more freedom for developer, especially if HDD installation is mandatory. Although HDD wasn’t a requirement for games for several years and I personally remember playing some relatively complex multidisk games from floppies, until I got a HDD to my Amstrad 2086, such as Eye of the Beholder.

I think this is a balancing act of convenience and what kind of limitations and challenges OP wants to have. As the OP said, the hardware changed when the CGA was commonly sold and used, so there is not one single correct answer and what OP suggested is certainly fine. If he wants to have bit more oomph by targeting faster 8086 CPU, there is absolutely nothing wrong with that. Borh CPUs are identical besides the bus unit, so there are no 8086 specific instructions which 8088 doesn’t have.

Um, Tim Paterson wrote 86-DOS on an S-100 system.
DOS was being created on an 8086 system with S-100 bus, rather than on an IBM PC.

https://en.wikipedia.org/wiki/86-DOS

Yes, and it is completely irrelevant to what OP is asking. He isn’t making a game for S100 system, but for PC/XT class machine with CGA graphics.

Blackthorn00 wrote on 2025-09-14, 10:25:

Thanks everyone for the super interesting discussion. I'm learning a lot of things. For the purposes of my game I can basically […]
Show full quote

Thanks everyone for the super interesting discussion. I'm learning a lot of things. For the purposes of my game I can basically summarize:

1) I need to make sure the game runs on 8088 rather than 8086 (I just assumed 8088 was the weirdo and 8086 was the standard, it's actually the other way around). This is not a problem.
2) I'll assume 256Kb of memory or more
3) I need to support either 2 360KB floppy drives OR 1 floppy drive + 1 10/20MB hard disk.
4) I need to downgrade the DOS version used. I was assuming MS-DOS 3.11 at least, but need to test with MS-DOS 2.1. Shouldn't be a problem but I need to recheck the software interrupts I use.
5) I'll assume an IBM compatible PC, both for my mental sanity and because I'm relying on BIOS interrupts to read keyboard, change video mode, etc. I also access video memory directly (interlaced CGA) and I don't think that works outside IBM universe. I also downloaded game manuals for some of the old CGA games (like Phantasie) and they pretty much all ask for an IBM compatible PC. (This is also consistent with what I remember from my childhood, where a friend of mine had an Olivetti and couldn't run all the games I could).
6) I didn't think about the keyboard! I was just assuming 102 keys and relying on scancodes to check for arrow pressed. I'll need to make the code work with XT keyboards as well, I guess. It would be nice if you folks could expand a little on that. How many keyboard layouts where there for IBM compatible PCs? (Let's ignore non IBM ones, since I'm just not going to support those).

Also I'm not planning to buy any hardware and mostly rely on 86Box for testing purposes (it's normally good enough, but it does allow for "fantasy" setups as well, which is why I created this thread). Very informative stuff folks, not sure why I waited so much before posting here 😀

Here is a quite good summary of PC keyboards up to PS/2 era and the differences between them:
https://dosdays.co.uk/topics/xt_vs_at_keyboards.php

Blackthorn00 wrote on 2025-09-13, 22:15:

I'm a bit surprised to read that Tandy was an outlier. I always assumed that Tandy 1000 was super popular and sold a shit-ton of units by being a cheaper IBM.

Tandy sold a lot of units for home use in the US, but that's a small subset of all early PCs sold. The vast majority of PCs were sold for business purposes. As a home computer, early PCs competed with things like the Commodore 64, Amstrad, Spectrum and MSX, which cost a fraction of the price, even of the price of Tandy's versions. It was in the corporate market that PCs became dominant. Then economies of scale started to push down prices and equally importantly, once companies started replacing their first gen PCs, those old machines flooded into homes en masse, giving so many homes those underpowered, underimpressive grey boxes of the late 1980s - exactly what you're targeting here.

But my comment on 'outlier' wasn't even related to absolute numbers, but rather to the hardware itself. It continued on the PCJr branch, deviating from regular PCs in a number of ways, both in terms of supporting shorter cards and - particularly relevant when the AT came along - different resource allocations. Hence Tandy video isn't completely CGA compatible(albiet a lot better than original PCJr was) and you can't use a replica of the Tandy sound card in a regular PC without a TSR to remap I/O port accesses. So tailor software for Tandy and you're not tailoring it to PC, unless you explicitly tailor it for the lowest common denominator of both.