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The red arrows mark the bus chips from our triumvirate of chip manufacturers, Motorola, National Semiconductor, and Texas Instruments.
The yellow box indicates one bank of the RAM chips from Mostek. Each chip is 8KB, making for a total of 64KB when you account for all eight chips.
The IBM PC Jr. does not have what we would consider a dedicated GPU. Instead it has the Motorola CRT controller marked in yellow.
Marked with a red arrow below that is a technical name Asynchronous Communication Interface Adapter. To me, that means modem - this chip would help process incoming information from an external modem.
Just to the right of the CRT controller is a chip, upside down in this photo, with the number SN76496N. That is the Texas Instrument sound chip.
The chip marked in yellow may be important, but I found it curious. I also found that I could not find information explaining what its function was. I would guess it has something to do with either the RAM expansion or the Internal modem.
Perhaps someone out there can share some insight concerning the chip in question?