ABSTRACT
Most computers support variable length instructions, and virtual address extension is an extreme case that has instruction from 1 to 21 bytes. In first generation computers, each machine instruction is one word long, so the instruction address register is a counter that contains a word address. In a second generation computer and beyond, an instruction may have many address fields, each one providing information on exactly how to find the operand. In a modern computer, the memory bus is etched on a printed circuit board so that single in-line memory modules can be inserted into the connector sockets. The internal operations in a computer can be described by register transfer language (RTL). The RTL describes the movement of bits from one location to another location in a computer. In general, supercomputers use 64-bit adders, the mainframes use 32-bit adders, and the microcomputers use 16-bit adders.
