CISC and RISC
CISC is a Complex Instruction Set Computer.
It is a MCU that can address a large number of instructions.
In the early 1980s, computer designers recommended that MCU should use fewer instructions with simple constructs so that they can be executed much faster within the MCU without having to use memory.
Such MCU are classified as Reduced Instruction Set Computer or RISC.
CISC vs RISC
The following points differentiate a CISC from a RISC
Von-Neumann Architecture and Harvard Architecture
Von-Neumann Architecture use only one bus for access to the data and to the code
Harvard Architecture use two or more separate buses for access to the data and to the code
Von-Neumann Architecture vs Harvard Architecture