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The IBM PC Jr. uses the Intel P8088 (red arrow) CPU, which was a very common CPU at the time. The yellow arrow marks a Programmable Interrupt Controller.
Before they went into the CPU cloning business, AMD made chips that supplemented the activity of the Intel 8088. The P8253-5 is a Programmable Interval Timer and the P255A is a Programmable Peripheral Interface.
This large chip is a Linear Encoder with IBM's name on it.