Inside & Out
From left to right, the sockets are:
J9, 10 and 11 (bottom left, middle and right, respectively) connect to the button board (J9 and J11) and display (J10), via ribbon cable.
The processor (the longest chip on the circuit board, middle right) is an Intel / Signetics 80C31, an 8-bit microcontroller with 128 bytes of onboard RAM, and an operating speed of 11 MHz.
Exact markings on the chip are: SC80C31BCCN40, 2299F02, 9001KE
The ROM chip is to the left of the processor, with a white sticker on it. It is a 32kb (8-bit), UV erasable/programmable ROM (EPROM).
Exact markings on the chip are: MMT-8 V1.10, A8AF (M), ALESIS, @ 7-22-89. Note that the release date for version 1.10 was 7-22-89. More about the differences between ROM versions here.
The two RAM chips are directly to the left of the ROM. Each chip is 256 kilobit (= 32 kilobyte).
Exact markings on the chip: SONY, CXK58257P-12L, JAPAN0129E. CXK refers to SONY, 58257 to the size of the memory, and P-12L to other parameters, such as access time.
The lithium battery (3.6 volts) is the purple cylinder on the bottom left of the circuit board.