Since register masks are a form of data embedded within the executable code, they can make linear parsing of the machine code difficult.
(The performance of the VAX-11/780 still serves as the baseline metric in the BRL-CAD Benchmark, a performance analysis suite included in the BRL-CAD solid modeling software distribution.) The VAX-11/780 included a subordinate stand-alone LSI-11 computer that performed microcode load, booting, and diagnostic functions for the parent computer. Enterprising VAX-11/780 users could therefore run three different Digital Equipment Corporation operating systems: VMS on the VAX processor, and either RSX-11M or RT-11 on the LSI-11.
The VAX went through many different implementations.
In time, as more programs were written in higher-level language, the instruction set became less visible, and the only ones much concerned about it were compiler writers.
One unusual aspect of the VAX instruction set is the presence of register masks These are arbitrary bit patterns that specify, when control is passed to the subprogram, which registers are to be preserved.
The name "VAX" originated as an acronym for virtual address extension, both because the VAX was seen as a 32-bit extension of the older 16-bit PDP-11 and because it was (after Prime Computer) an early adopter of virtual memory to manage this larger address space.
Early versions of the VAX processor implemented a "compatibility mode" that emulated many of the PDP-11's instructions, and were in fact called VAX-11 to highlight this compatibility and that VAX-11 was an outgrowth of the PDP-11 family.In June 1990 Vax contracted James Dyson to produce an upright vacuum cleaner aimed at the British market. By July 1991, he had left the company to produce this product independently.VAX is a discontinued instruction set architecture (ISA) developed by Digital Equipment Corporation (DEC) in the mid-1970s.The original VAX 11/780 was implemented in TTL and filled a four-by-five-foot cabinet with a single CPU.CPU implementations that consisted of multiple ECL gate array or macrocell array chips included the VAX 86 superminis and finally the VAX 9000 mainframe class machines.Later versions offloaded the compatibility mode and some of the less used CISC instructions to emulation in the operating system software.