John Hasler wrote:
Dave Hart writes:
I believe it had more to do with the Color Graphics Adapter circuitry
needing to operate at NTSC-compatible frequency.

According to my Technical Reference manual the XT and the Portable PC
used a 14.31818MHz crystal.  This was the only crystal on the
motherboard.

Did the XT have an RTC?  The original PC certainly did not.

The AT has at least two crystals (4* NTSC and 32768kHz).

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