IBM AT 5170 Technical Reference page 430

The following table identifies the microprocessor and describes
the I/O channel used with each type of IBM Personal Computer.
System Unit
System Name Microprocessor
I/O Channel Description
Personal Computer 8088 5 62-Pin
PCjr 8088 Not Compatible
Personal Computer XT
8088
8 62-Pin
Portable Personal
8088
8 62-Pin
Computer
Personal Computer AT 80286 2 62-pin
6 98-Pin (62 Pin
+
36 Pin)
System Hardware Identification Chart
The faster processing capability of the 80286, compared to the
8088, creates special programming considerations, which are
discussed later in this section under "Application Guidelines."
Some adapters use a 36-pin connector in addition to the 62-pin
connector. Adapters designed to use the 36-pin connectors are
not compatible with all members of the IBM Personal Computer
family. Refer to the "System to Adapter Compatibility Chart" in
r"'­
the Technical Reference Options and Adapters manual, Volume 1,
to identify the adapters supported by each system. The IBM
Personal Computer AT does not support an expansion unit.
On the IIO channel:
• The system clock signal should be used only for
synchronization and not for applications requiring a fixed
frequency.
• The 14.31818-MHz oscillator is not synchronous with the
system clock.
• The ALE signal is activated during DMA cycles.
• The -lOW signal is not active during refresh cycles.
• Pin B04 supports IRQ 9.
9-4 Compatibility