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The DEC VAX CPU is a legendary CISC CPU prized and praised by many low level assembly language coders. The CPU was used in many systems from the 1970's up until the 1990's. The acronym VAX came from the phrase “virtual address extension” this is because it's primary goal was to increase the address space of the PDP-11 which was a 16-bit machine. DEC was a very early implementer of the technique of using virtual memory. RAM was very expensive in those days. There were even compatible modes for the PDP-11 on early VAX machines, but later that capability was taken over by software based emulation. For more technical history on the VAX, we definitely recommend the Wikipedia article on the VAX.

The thing to understand about the DEC VAX is that it's a dyed-in-the-wool CISC processor. There were many system programmers writing code in MACRO32 (VAX assembler) and this resulted in a CPU that was much easier to write assembly language for. The VAX instruction set saves the programmer time and hair-pulling. The often unspoken truth is that it resulted in superior results even at the compiler level. After all, if you were writing a compiler would you rather have CISC or RISC to contend with? So, what we've seen is that folks hold their nose long enough to get code done on the Alpha or Itanium. However, back in the VAX days they took their time to do it right. After all the helpful instructions made it easier and more fun. So, this is one theory as to why code quality has suffered so badly after the 1980's and 1990's.

digital_vax_systems.txt · Last modified: 2018/11/16 22:13 by sgriggs

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