Each phrase in List II is a term of art belonging to exactly one device: a-iv, b-i, c-ii, d-iii — option 3.

a — maximum mode. The 8086 has a pin that selects between two modes. In minimum mode it generates its own control signals and works as a single processor. In maximum mode it emits three status lines instead, and an external 8288 bus controller decodes them — which allows a coprocessor such as the 8087 or another bus master to share the system bus, arbitrated by the 8289. The mode exists specifically for multiprocessor systems.

b — the 128 bytes. The 8051 is a microcontroller: processor, memory and peripherals on one chip. Its on-chip data RAM is 128 bytes, of which the lower 32 are the four register banks and the next 16 are bit-addressable. The figure is small because the RAM is for variables and stack only; program code lives in the separate 4 KB of ROM, the Harvard split that distinguishes the 8051 from the 8085.

c — two-key lockout. A keyboard-scanning controller must decide what to do when two keys are pressed at once. The 8279 offers two policies: two-key lockout, which ignores both unless one is released first — the safer choice, preventing spurious entries from a clumsy keystroke — and N-key rollover, which enters each key independently in the order detected, preferred for fast typing. The 8279 also debounces and buffers up to eight keystrokes in a FIFO.

d — the three-chip system. The 8085's best-known selling point was that a complete microcomputer needed only three chips: the 8085 processor, an 8155 (RAM, I/O ports, timer and address latch) and an 8355 or 8755 (ROM with I/O ports). Because those support chips contain the address latch that demultiplexes the AD bus, no glue logic is required at all — a considerable advantage in 1977.

Hence, the correct code is a-iv, b-i, c-ii, d-iii.