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Intel C8253 Intel 8253 programmable interval timer. Intel 8254 has the same pinout. The Intel 8253 and 8254 are programmable interval timers (PITs), which perform timing and counting functions using three 16-bit counters. [1] The 825x family was primarily designed for the Intel 8080/8085-processors, but were later used in x86 compatible systems.
The Intel 8253 PIT was the original timing device used on IBM PC compatibles. It used a 1.193182 MHz clock signal (one third of the color burst frequency used by NTSC, one twelfth of the system clock crystal oscillator, [1] therefore one quarter of the 4.77 MHz CPU clock) and contains three timers.
The clock rate of the PC's programmable interval timer which drives the speaker is fixed at 1,193,180 Hz, [3] and the product of the audio sample rate times the maximum DAC value must equal this. Typically, a 6-bit DAC [8] with a maximum value of 63 is used at a sample rate of 18,939.4 Hz, producing poor but recognizable audio. [9]
This optional but default feature is new with 2.6.18. When enabled on a computer with an APIC timer, the kernel does not use the 8253 programmable interval timer for timekeeping. [12] A VMware document notes that "software does not have a reliable way to determine its frequency. Generally, the only way to determine the local APIC timer’s ...
The references to two timers is not true. In Intel ICH4 documentation, the timer exists in IO ports 40h..43h, and the same timer is aliased to IO ports 50h..53h for some reason. A very good guess would be that the original IBM PC had it like this too to simplify IO address decoding, but this is just a guess.
The Time Stamp Counter was once a high-resolution, low-overhead way for a program to get CPU timing information. With the advent of multi-core/hyper-threaded CPUs, systems with multiple CPUs, and hibernating operating systems, the TSC cannot be relied upon to provide accurate results — unless great care is taken to correct the possible flaws: rate of tick and whether all cores (processors ...
The High Precision Event Timer (HPET) is a hardware timer available in modern x86-compatible personal computers. Compared to older types of timers available in the x86 architecture, HPET allows more efficient processing of highly timing-sensitive applications, such as multimedia playback and OS task switching .
On March 6, 2000, AMD demonstrated passing the 1 GHz milestone a few days ahead of Intel shipping 1 GHz in systems. In 2002, an Intel Pentium 4 model was introduced as the first CPU with a clock rate of 3 GHz (three billion cycles per second corresponding to ~ 0.33 nanoseconds per cycle). Since then, the clock rate of production processors has ...