no official relationship.
However if you search this forum you will find various people claiming certain values correspond with certain PCs.

mmoreira wrote:

I mean, it´s possible to say, per example, that when i set up CPU Cycles to 5000 it is equivalent to a 40mhz machine? (5000 and 40 are arbitrary examples)

40MHz 386 or 40MHz 486? 😉

mmoreira wrote:

Hi, first, I don´t know if this is a dumb question, sorry if it is. […]
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Hi, first, I don´t know if this is a dumb question, sorry if it is.

My question is: Is there any relationship between how many cpu cycles are emulated and what speed this is represents in mhz?

I mean, it´s possible to say, per example, that when i set up CPU Cycles to 5000 it is equivalent to a 40mhz machine? (5000 and 40 are arbitrary examples)

What I want with this is "re-create", as close as possible, my old 286 16mhz machine, or my old 386sx 33.

It is possible or what i'm asking makes no sense / is impossible?

Thank you guys, sorry for my poor English. 😀

well, the way I understand things you should concentrate on getting the applications you want dosbox to run going at the speed and stability you require, which .conf settings may vary for each one, rather than aiming to recreate a specific machine.

You could take a look at the DOOM benchmark for some comparison values. Then do the benchmark on your DOSBox. 😁
http://www.complang.tuwien.ac.at/misc/doombench.html

Comparing benchmarks created on "metal" to ones created in an emulator is like comparing apples to pears. If it wasn't for that smiley I'd say you have no idea what you're talking about.

TomJeffersonJones hit the nail on the head. Why go to lengths in trying to reproduce something you only vaguely remember anyway when you can just tweak DOSBox to run the game you want to play at perfect (=perfectly playable) speed. If you want to "reproduce" old machines do it in hardware.

Um.. nostalgia perhaps? 😅

mr_bigmouth_502 wrote:

Um.. nostalgia perhaps? 😅

well like addict says, if you're nostalgic for a particular machine track down the parts and software, put it all together and hit the switch.

Most of us are nostalgic for the programs ... in which case filling our .conf with arbitrary settings that we think coincide with this machine or that is a chimera. The program will tell you what it needs from Dosbox, listen to the program.

Officially, there is no such relation. But I've run the Check It tests and Norton tests, and I got some values to match 4.77, 8 and 10 MHz 8086 PCs... but I've lost the data.

I used that data to play some games that did not have "throttle" control (for example, try to play "Freddy Hardest" without limiting cycles) or have fixed options (usually 4.77, 8 MHZ 8086 and some 286 options). Most modern games uses other methods to control speed, so it is not necessary limiting cycles.

BTW, to limit speed you'll need a performance tester, and performance data of the "typical" system. With some luck, you may tune your cycles to match those of the target system.

Also, keep in mind that some operations are faster in DOSBox than in your target system (and that's the reason because there is no official relationship).

Officially, there is no such relation. But I've run the Check It tests and Norton tests, and I got some values to match 4.77, 8 and 10 MHz 8086 PCs... but I've lost the data.

And inofficially, there's no relation as well. Depending on the instruction set
the benchmark is using, you can get any "relationship" you want. That's sort
of a problem for general apps/games as well but most are synchronized to external
events so it's nicely playable.

In my experience, 10,000 cycles often give about the same speed as my old 66MHz 486. There are exceptions, though.

CPU Speed Question

Read HAL's post at the bottom of the thread.

Again: this doesn't account for the x86's different number of clocks per instruction for the instructions.

Hence the "roughly"

cpi for DEC ~2, for fpu stuff >100, calculate yourself how "rough" that is.
But i don't really care what you make people believe of course 😉

Ok, I hope this question won't piss anybody off, but is there a reason why the different CPI are not (roughly) taken into account by the speed-limiter built into DOSBox? At least for the pre-pipeline processors up to the 386 you should be able to get a more or less fixed value for every opcode / adressing mode combination from some table, no?

I guess the answer is simply "it's not needed for games", right?

I fail to see how you'd account for the load take up by other programs on the system considering alot of people use DOSBox while they are doing other things on their computer.

Only feasible solution would be to force affinity to a seperate core but then you'd have to implement checks for single/multi-core users and you'd still have the performance difference between different processors to account for.

and yeah it's mostly not needed since compatibility has been (and likely always will be) a greater concern.

tearex, yeah not needed and would slow down dosbox a bit.