Divide Overflow
Microsoft MS-DOS
Severity: ModerateWhat Does This Error Mean?
Divide Overflow means a program attempted a division that produced a result too large for the CPU register, or divided by zero. This is usually caused by running software on a CPU that is too fast for the program's timing loops. Slowing down the CPU or using a slowdown utility often fixes it.
Affected Models
- MS-DOS 3.x
- MS-DOS 4.x
- MS-DOS 5.x
- MS-DOS 6.x
- PC-DOS
- FreeDOS
- DOSBox
Common Causes
- Program uses CPU speed for timing and the CPU is too fast
- Software written for 4.77 MHz 8088 running on a 486 or Pentium
- Division by zero in the program code
- Timer-based calculation overflows because clock ticks happen faster than expected
- Incompatible TSR program interfering with the timer interrupt
How to Fix It
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If running on real hardware: use a slowdown utility like MOSLO or BREMZE.
These utilities artificially slow the CPU to match the speed the program expects. MOSLO is the most well-known DOS slowdown tool and works with most programs.
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If running in DOSBox: reduce the CPU cycles.
Press Ctrl+F11 in DOSBox to reduce CPU speed. Or edit dosbox.conf and set cycles=1000 or cycles=auto. Many old games need very low cycle counts to avoid Divide Overflow.
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Check if a patched version of the program exists.
Some popular games and applications were patched by fans to fix speed-related crashes. Check DOS game archives for updated versions.
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Try running the program with Turbo mode disabled on your PC.
Many 386 and 486 PCs had a Turbo button that switched between fast and slow CPU speed. Disabling Turbo mode (pressing the button so the light goes off) can slow the CPU enough for older software.
Frequently Asked Questions
Why do old DOS games crash on fast computers?
Many DOS games from the 1980s used the CPU clock speed for timing — they counted how long operations took and assumed a 4.77 MHz or 8 MHz processor. On a faster CPU, the timing loops complete instantly, causing division results that overflow the CPU's registers.
What was the Turbo button on old PCs?
The Turbo button toggled between the PC's full speed and a slower compatibility mode (usually 4.77 or 8 MHz). It was specifically designed to let users run older software that crashed on faster hardware — the exact problem that causes Divide Overflow.