...except it barely more of a 16 bit processor than a Z80, and had 8 bit instructions, extendable to longer, like the Z80. Aside from the 20 bit addressing and 16 bit offset, the 8088 and Z80 were equivalent.

Or should we call the Z80 a 16 bit processor?

> Or should we call the Z80 a 16 bit processor?

Z80 is classified as an 8-bit processor because it has an 8-bit internal data bus to the register file.⁽¹⁾

This is visible in instruction timings: 16-bit INC BC takes longer than 8-bit INC B because the 16-bit register access takes two internal data cycles compared with one internal cycle for 8-bit.

Intel 8086 is classified as a 16-bit processor because it has a 16-bit internal data bus to the register file.

This is visible in instruction timings: 16-bit register operations generally take the same time as 8-bit register operations.⁽²⁾

⁽¹⁾ Trivia: Z80 also has a 16-bit internal address bus and 4-bit ALU.

⁽²⁾ Actually 8-bit INC AL takes longer than 16-bit INC AX, opposite way around from Z80. But that's because of a longer instruction encoding, not architecture. MOV AL,BL takes the same time as MOV AX,BX.)