Microprocessor - IBM XT 5160 Technical Reference

Microprocessor
The heart of the system board is the Intel 8088 Microprocessor.
This is an 8-bit external-bus version of Intel's 16-bit 8086
Microprocessor, and is software-compatible with the 8086. Thus,
the 8088 supports 16-bit operations, including multiply and
divide, and 20 bits of addressing (1M byte of storage). It also
operates in maximum mode, so a coprocessor can be added as a
feature. The microprocessor operates at 4.77MHz. This
frequency is derived from a 14.31818MHz crystal, the frequency
of which is divided by 3 for the microprocessor clock, and divided
by 4 to obtain the 3.58MHz color-burst signal required for color
televisions.
At the 4.77MHz clock rate, the 8088 bus cycles are four clocks of
210 nanoseconds (ns) each, or 840ns total. Some I/O cycles take
five 210ns clocks or 1.05 microseconds (J-ts).
1-4 System Board