Difference between revisions of "Configuration:CPU"

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The CPU section controls how DOSBox tries to emulate the CPU, how fast the emulation should be, and to adjust it. DOSBox offers 4 different methods of [[/cpu/core/Intro|CPU emulation]].
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Baby, we've come a hell of a long way.
 
 
==== core = [[/cpu/core/simple|simple]] | [[/cpu/core/normal|normal]]| [[/cpu/core/dynamic|dynamic]] | auto ====
 
[[/cpu/core/Intro|CPU core]] used in emulation. The choices result in a different efficency of DOSBox and in very rare cases have an effect on stability.
 
 
 
:{| class="wikitable"
 
|-
 
| '''normal''' || The program is interpreted instruction by instruction. This approach is a lot more CPU demanding than dynamic core but allows for a more fine-grained time emulation and is needed on platforms for which DOSBox doesn't have a dynamic core.
 
|-
 
| '''simple''' || Basically the same as normal, but optimized for real-mode (older) games. In case a protected-mode game is started, it automatically switches back to normal core.
 
|-
 
| '''dynamic''' || The program instructions are, in blocks, translated to host processor instructions that execute directly. See also [http://en.wikipedia.org/wiki/Just-in-time_compilation ]. In the most cases this approach is more efficent than interpretation, except for programs that employ massive self-modifying code. This option is not present on all host platforms.
 
|-
 
| '''auto''' || Real-mode programs are run with the normal core. For protected mode programs it switches to dynamic core, if available.
 
|-
 
| '''full''' || Deprecated. 
 
|}
 
 
 
Default is '''auto'''.
 
 
 
==== cputype = auto | 386 | 386_slow | 486_slow | pentium_slow | 386_prefetch ====
 
CPU Type used in emulation. '''auto''' is the fastest choice.
 
 
 
:(since 0.73)
 
 
 
Default is '''auto'''.
 
 
 
==== cycles = fixed ''nnnn'' | max [''default''%] [limit ''cycle limit''] | auto [''realmode default''] [''protected mode default''%] [limit "cycle limit"] ====
 
Amount of instructions DOSBox tries to emulate each millisecond. Set to '''max''' to automatically run as many cycles as possible.  '''auto''' setting switches to '''max''' if appropriate.
 
 
 
:{| class="wikitable"
 
|-
 
| '''fixed ''nnnn'' ''' || Sets the emulated CPU speed to a fixed amount of cycles (''nnnn''). A value of 3000 equates 3 MIPS. If this value is too high some games will run too fast or crash. How high you can go depends on the power of your host CPU and on the selected core (above). If the value is too high for your CPU the emulation will slow down and the sound starts to skip.
 
|-
 
| '''max''' || Automatically sets the cycles so approximately the (optional) ''default''%-value of your host CPU is used. If the value is not specified it defaults to 100%. The optional ''limit'' parameter limits the maximum speed to the specified value.
 
|-
 
| '''auto''' || For realmode games, this option switches to ''realmode default'' number of cycles or 3000 if not specified. When switching to protected mode, cycles is internally switched to '''max''' using the remaining optional parameters.
 
|}
 
 
 
Default is '''auto'''.
 
====== Examples: ======
 
* ''cycles=fixed 5000'', ''cycles=5000'' - All games you start are run with a fixed speed of ~5 MIPS. Useful for speed sensitive games or games that need a continuous CPU speed. You can change the actual value with Ctrl+F11 and Ctrl+F12 ([[SpecialKeys|keycombo]]) while DOSBox runs.
 
* ''cycles=max'' - All games you start run at the maximum speed your CPU permits. Use Ctrl+F11 and Ctrl+F12 to change the percentage of your CPU to be used.
 
* ''cycles=max limit 50000'' - All games you start run at up to 50000 cycles, depending on the power of your CPU.
 
* ''cycles=max 50%'' - About 50% of your CPU power will be used.
 
* ''cycles=auto'' - Realmode games will run at 3000 cycles. Protected mode games run with ''cycles=max''.
 
* ''cycles=auto 5000 50% limit 50000'' - Realmode games run with 5000 fixed cycles, protected mode games with ''cycles=max 50% limit 50000''.
 
 
 
==== cycleup = ''nnn'' ====
 
Amount of cycles to increase with [[SpecialKeys|keycombo]].
 
 
 
Default is '''10'''. Setting it lower than 100 will be a percentage of the current value.
 
 
 
==== cycledown = ''nnn'' ====
 
Amount of cycles to decrease with [[SpecialKeys|keycombo]].
 
 
 
Default is '''20'''. Setting it lower than 100 will be a percentage of the current value.
 

Revision as of 01:57, 18 November 2015

Baby, we've come a hell of a long way.