The design of a computer system. It sets the standard for all devices that connect to it and all the software that runs on it. It is based on the type of programs that will run (business, scientific) and the number of programs that run concurrently.
Space and Time
All components in a computer are based on space (how much) and time (how fast). One example is the amount of memory a computer can access and how fast it can access it. Another is the width of the channels (16-bit, 32-bit, etc.) between the CPU and memory and between the CPU and peripheral devices and how fast they transfer data.
CISC vs. RISC
The way a computer's instructions are designed is a fundamental architectural component. The trend toward large, complicated instruction sets was reversed with RISC computers, which use simpler instructions. The result is a leaner, faster computer, but requires that the compilers generate more code for complex functions that used to be handled in hardware. Both CISC and RISC architectures are widely used. See RISC
Computers designed for single purposes, such as vector processors and database machines, require special architectures. In addition, computers designed from the ground up for fault tolerance also require unique designs.