V20 allows you to “play” (use that word loosely)
wolfenstein 3d without recompiling code.

Several Windows 3.0 drivers work with a v20 but not the original 8088

Are you sure for Wolf 3D ? I thought it needed a 286.

There are lots of games that are sluggish on an 8088. Making them up to 20% faster obviously helps, but all of these games really play best on a 286 or better anyway.

IMO I think the increase in speed is not worth the trade off in compatibility and authenticity. Speed sensitive games run just a bit too fast, and maybe 5%-10% of early DOS games won't run at all on the NEC V20. On a clock switchable motherboard, I think a 10mhz rated 8088 is better. For the vast majority of games made before 1988, a 4.77mhz 8088 is exactly what what you want.

Agreed. Is there an actual clock-switchable 10mhz 8088 though? My Tandy SX has a "8088-2" which can do authentic 4.77 or 7.16mhz (sometimes referred to as 5mhz and 8mhz). I don't think there were actual authentic 8088 CPUs rated higher?

There are 8088 CPUs rated for 10mhz.

Deksor wrote:

Are you sure for Wolf 3D ? I thought it needed a 286.

It doesn't use 286 specific instructions. An 8088 is a 16 bit cpu on an 8 bit bus. Similar to how a 386sx is a 32 bit cpu on a 16 bit bus. For games, the bus is usually the bottleneck but a higher cpu speed also give you a slightly higher bus speed.

No games benefited from a V20 alone.
Games designed for 8088@4.77 can only exhibit some timing problems when run on V20@4.77
Games designed for later CPUs will be too slow on V20@4.77
Games using 186/286 instructions may run on V20@4.77, but again - too slow.

However, V20 CPUs are usually coupled with turbo, and there's a big difference between 8088@4.77 and eg. V20@12

Deksor wrote:

Are you sure for Wolf 3D ? I thought it needed a 286.

The 286 is the 186 with protected mode. The V20 is 186 compatible. Since Wolf3D doesn’t use protected mode it should start up on a V20. Maybe someone here can verifiy?

Look at YouTube, people did that already. Barely playable with smallest window size.

this cpu would have been wonderful with more MHz - bottom line
the same for 286 as well btw

the games that ran on 186 probably are candidates

https://en.wikipedia.org/wiki/Flashback ... ideo_game) run fine with V20 and not run with 8088 at all.

Grzyb wrote:

However, V20 CPUs are usually coupled with turbo, and there's a big difference between 8088@4.77 and eg. V20@12

The thing is, in this configuration, the turbo is what makes all the difference. And it's limited to whatever clock rate the original CPU had. You can't run a V20 at 12MHz in a 5150, and what is the benefit in running a V20 at 7.14MHz instead of a 8088-2 at the same clock speed in a Tandy?

Tronix wrote:

https://en.wikipedia.org/wiki/Flashback ... ideo_game) run fine with V20 and not run with 8088 at all.

That's interesting. Though now we run into an anachronism, as if I recall correctly, Flashback was VGA only.

I think Monkey Island (not sure if it was 1 or 2) is another game that uses 186 instructions (made for AT machines, so 286 CPUs, but does not use protected mode).

Note also that the V20 is not 100% compatible with the 8088. Specifically it does not implement some undocumented instructions, which may or may not have been used in games.
8088 MPH uses some of these instructions, more specifically 'SALC', see here: https://www.pcjs.org/pubs/pc/reference/intel/8086/

Scali wrote:

I think Monkey Island (not sure if it was 1 or 2) is another game that uses 186 instructions (made for AT machines, so 286 CPUs, but does not use protected mode).

Note also that the V20 is not 100% compatible with the 8088. Specifically it does not implement some undocumented instructions, which may or may not have been used in games.
8088 MPH uses some of these instructions, more specifically 'SALC', see here: https://www.pcjs.org/pubs/pc/reference/intel/8086/

I think Monkey Island can run on an 8088. At least I have seen video of it running on the first compaq protables, which I believe used a real 8088 processor.

In real life a V20 offers a low single digit % improvement, those 20% are benchmarks that absolutely benefit from a V20. In other words 20% is the largest difference you can see when trying to see it in non-realistic conditions. Expect a realistic ~5%. Which is of course important, I'm not mentioning it as a small improvement. Having said that, a V20 will allow you to run a few things that don't work on a 8088 and use 186 instructions (dos' edit is a popular one) but you don't get an XT nowadays to count FPS. Don't expect to run games targeting AT with it, they are not playable. But it certainly helps in games that run almost perfectly on an XT, games that were meant to be played on an AT but were also playable, albeit sluggish, on an XT.

Also yes, of course the first monkey island runs on an 8088. May of us grew up with it 😉 If one needs at least an 80186 then it's #2

konc wrote:

...a V20 will allow you to run a few things that don't work on a 8088 and use 186 instructions (dos' edit is a popular one)...

Back in the days I was very tight on storage space. So I grabbed every opportunity to save as much as possible and I compressed many of my programs/games with pklite. Later when I tried to run said old games on a fresh retro 8088 system I got nothing but they still work with a V20.

So if someone did the same to Monkey Island 1, then it could explain why it can't run on an XT.

Just my 2 cents.

mothergoose729 wrote:

maybe 5%-10% of early DOS games won't run at all on the NEC V20.

I've always thought the general consensus was 99% of games WILL RUN on a NEC v20 that will run on a 8088. Can anyone name one game other then that one version of Lode Runner that will fail to run on a V20?

soviet conscript wrote:

mothergoose729 wrote:

maybe 5%-10% of early DOS games won't run at all on the NEC V20.

I've always thought the general consensus was 99% of games WILL RUN on a NEC v20 that will run on a 8088. Can anyone name one game other then that one version of Lode Runner that will fail to run on a V20?

Of the 55 games I have tested released between 1981 and 1984, I have found two games. They use text based graphics, and they don't work on my NEC V20 but do work on in DOSBox. I don't have an 8088 CPU right now to compared. I have a lot more games that don't work on my particular computer, but I can't be sure if it is my trident SVGA card that is incompatible or the CPU (probably the VGA, I'll need to get an IBM CGA card to be sure).

Chess 1981 (text based monochrome graphics)
Startrek 1981 (text base monchrome graphics, string parse error)

Beyond that though, the speed in certain DOS games definitely feel a bit too fast, even at 4.077mhz. This compared to running the same game in DOSBox at 315 cycles, which is what is recommended for a 4.77mhz 8088.

Atari's Centipede
William's Defender
Lode Runner (the compatible version)

There are also some games that I haven't been able to get working in either DOSBox or on my XT clone board. These could just be bad dumps, so I'll need to do more research.

1981 Rocket
1982 Lunar Landing
1983 Miner 49er
1983 The Hobbit

So 5%-10% of early DOS games as an estimate is probably way too high. However, given the choice, I still think an 8088 CPU makes more sense from a retro perspective. Any game that you can run on a NEC V20 that you can't on an 8088 is almost certainly too slow to be worthwhile, and there are some games that don't work on the NEC V20 or run too fast.

mothergoose729 wrote:

Beyond that though, the speed in certain DOS games definitely feel a bit too fast, even at 4.077mhz. This compared to running the same game in DOSBox at 315 cycles, which is what is recommended for a 4.77mhz 8088.

DOSBox isn't exactly very accurate. 315 cycles is just a ballpark figure, but how it actually compares to a real 8088 depends on the instruction mix used by the game.
In DOSBox, all instructions are equally fast. On a real 8088, there are huge differences in execution speed between instructions.