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I wonder what VAX would be capable of today if they had the same level of resources as e.g. Intel. From what I've seen there are some super-powerful instructions, but the opcode map[1] is extremely irregular - even x86 has an octal structure to it - so superscalar decoding would be far more difficult. It's also not as compact of an encoding as x86, so the code density would be lower; x86, despite being CISC, tends to have more frequently used instructions be shorter, e.g. ~1/4 of the 1-byte opcode map is register-register/register-memory ALU operations.

[1] https://www.cs.auckland.ac.nz/references/macvax/op-codes/VAX...

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DEC deliberately moved away from VAX to work on Alpha, which performed quite well for its time.

John Mashey made some interesting comments on the (lack of) future prospects for the VAX here: http://yarchive.net/comp/vax.html

The best thing I remember was PALcode: a nice cross between microcode and assembler. So many uses for that: accelerators, atomic operations, security primitives, and so on. I really wish the x86's had that feature instead of their SMM, etc garbage.

ctrl+f "FUNDAMENTAL PROBLEM" to find his writeup of the actual difficulties of fast VAX implementations, including ways that x86 is easier than VAX. The big whammy is string ops where the length operand can be indirectly-addressed.

x86 string ops, which are a lot simpler, were slow until pretty recently.

But reading http://web.eece.maine.edu/~vweaver/papers/iccd09/iccd09_dens..., Alpha didn't have high code density. Caveat here is that they may have been better at hand-optimizing CPUs they are familiar with or where information is easier to Google. That would favor x86, for instance. Note, however, that they get way smaller code for PDP-11 and VAX than for Alpha.

Due to the way instruction fetch and dispatch worked on the first few generations of the Alpha, you had to put in lots of NOPs to get decent performance.

Does anyone know the inside story behind the Titan [1], and what ever became of it? Brian Reid showed me a room full of them when I visited him at DECWRL in Palo Alto by the greasy transformer vault [2], and they seemed vastly majestic and toasty warm. I bet they really kept that rancid grease hot!

[1] https://archive.org/stream/bitsavers_dectechrep_207144/WRL-8...

[2] http://milk.com/wall-o-shame/bucket.html

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