![]() ![]() Turbo PC by Complete Business Systems, - 1994, Ira Kleiner.This is used for power saving or to prevent CPU overheating rather than for compatibility, as modern applications use the real time clock for timing instead of the CPU clock. Modern PCs that support ACPI power management may provide software controls to switch ACPI performance states or other CPU throttling modes. ![]() One example is DOSBox, which offers an adjustable emulation rate. While the implementation of an actual hardware turbo button has disappeared on modern machines, software developers have compensated with software replacements. As software began to rely on other timing methods, the turbo feature became mostly irrelevant to new programs. The frequency displays largely disappeared or were reprogrammed to display "HI"/"LO" when CPU speeds reached 100 MHz, since most systems only had a two-digit display.Īs new computers continued to get faster and had a wide variety of available speeds, it became impossible for software to rely on specific CPU speed. The feature was relatively common on systems running 286 to 486 CPUs, Īnd rarely on first generation Pentium CPU equipped computers. Unlike the turbo button that was common on computer cases, the turbo button on the keyboards did not control the clock rate of the CPU rather, it controlled the keyboard repeat rate. Some keyboards had a turbo button as well, located near right Shift. With all the 486ES models-those with and without a turbo button-the power light would show green in normal (“Turbo”) mode, and orange in Slow mode. Some systems also supported keyboard combinations Ctrl- Alt- + and Ctrl- Alt- for switching turbo mode on and off, such as the Packard Bell 486ES 3x3 (the 4x4 and MT models had a dedicated Turbo button). On most systems, turbo mode was with the button pushed in, but since the button could often be wired either way, on some systems it was the opposite.The turbo button could be linked to a turbo LED or two-digit segmented display on the system case, although in some cases, the indicated frequency (in MHz) was not a measure of the actual processor clocks, but the two "fast" and "slow" display options set by jumpers on the motherboard. Disengaging turbo mode slows the system down to a state compatible with original 8086/ 8088 chips. To provide some compatibility, the "turbo" button was added. Games in particular were often rendered unplayable. With the introduction of CPUs which ran faster than the original 4.77 MHz Intel 8088 used in the IBM Personal Computer, programs which relied on the CPU's frequency for timing were executing faster than intended. ![]()
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