VAX ARCHITECTURE( Virtual Address Extension )

• The VAX-11/780 introduced virtual memory support and a more advanced instruction set, marking a significant evolution from the DEC PDP-11 family.
• The VAX-11 architecture was engineered to address the inherent limitation of the PDP-11's constrained address space, ensuring compatibility with a broader range of applications.
• The Virtual Address extension (VAX) increased the address from 16 to 32 bits.
• VAX architecture features 16 general-purpose registers, contrasting with architectures like MIPS, SPARC, or PowerPC, which typically have 32.
• Among these 16 registers, the program counter (PC) is integrated into the set rather than being a separate register.
• Additionally, one of the registers serves as the stack pointer, while condition codes similar to those found in PowerPC architecture are also present.
• The extension provided 4.3 gigabytes of virtual address space.
• VAX-11/780 was the first implementation of the VAX-11 architecture.
• Extreme Orthogonality: In VAX architecture, operands can be specified independently of the opcode, allowing various addressing modes to be combined with any instruction.