3 ms·

Alpha would have been such a better path to follow, and Intel even ended up with a license for it because of Compaq/HP's incompetence.

o11c 3y ago
Alpha was unequivocally terrible though. "Better than Itanium" is really not saying much. * no byte operations * no flags, thus no reasonable way to check for overflow (similar to one of the problems RISC-V is having, though at least they pretend to care).
- masklinn 3y ago
  Also “notoriously weak” memory model even as multithreading was taking off, and > The processor may lose track of your LDx_L if you perform any memory access other than a matching STx_C, or if you perform a branch instruction, or if you trigger a trap (such as executing an emulated instruction), or if you execute more than 20 instructions after the LDx_L. (LDxL and STxC are locked load and conditional store)
  - colejohnson66 3y ago
    What do you mean “lose track of”?
    - masklinn 3y ago
      Discard / clear the lock flag, so I assume the store never succeeds (but the behaviour could be less consistent).
  - pm215 3y ago
    That is pretty standard for LL/SC instructions -- you'll find similar constraints on the Arm equivalent insns. In practice this doesn't matter because you only use them in a limited set of handcoded sequences to implement the atomic primitives you actually wanted, so you can always be sure that your LL/SC loop obeys the rules and makes forward progress.
    - cmrdporcupine 3y ago
      Was going to say. x86 I think has spoiled people in terms of what they expect in terms of memory model / consistency. The answer is to be careful as a dev, and hopefully let the compiler and your libraries take care of the finer details.
- jabl 3y ago
  IIRC they did add byte operations pretty soon after the initial generation. The memory consistency model was pretty crazy, though.
jmyeet 3y ago
Two fun facts about DEC Alpha: 1. Windows NT, which is the ancestor of modern Windows, was originally released on multiple platforms including Alpha and, I believe, MIPS; and 2. DEC, for awhile at least, had one of the most popular Web search engines: AltaVista. It wasn’t a commercial enterprise. It was mostly a technology demonstration for Alpha. For the time it was pretty good. No one at this time (the 1990s) thought there was a future in search engines. Many (including Yahoo) seemed to think curated directories were the future. Search engines were viewed as a solved problem, except by Larry Page and Sergei Brin who founded Google. The highly underrated show “Halt and Catch Fire” covers this early era of computing really well and is worth watching.
- ngcc_hk 3y ago
  When Windows NT and DEC is in the same message, may I suggest to mention that Windows NT is developed essentially by the DEC team.
  - gbin 3y ago
    I highly recommend watching the recent interview of Dave Cutler, it gives some perspective on that https://youtu.be/xi1Lq79mLeE?si=D8_40BPga4Qj5jsW https://youtu.be/xi1Lq79mLeE?si=D8_40BPga4Qj5jsW
javitron 3y ago
Itanium was being defined around the same time the 1st Alphas came to market. By the time Itanium2 came out, it matched/surpassed the contemporary AXP parts. FWIW the alpha design teams ended up cannibalized between AMD and Intel. The original Opteron and the first generations of Core i have a ton of AXP DNA in them, from a uarch standpoint. So in a sense, Intel and AMD did continue Alpha... sort of. However. I feel that Alpha gets over fetishized on the internet sometimes. It was a clean arch, mainly because it was a clean 64bit design from the get go. But as far as uArch, it was pretty generic. Most of the uArch themes the AXP design teams used, which a lot of people think were native inventions to Alpha, came straight from industry/academia research, and plenty of other processors implemented them as well.

o11c 3y ago

Alpha was unequivocally terrible though. "Better than Itanium" is really not saying much. * no byte operations * no flags, thus no reasonable way to check for overflow (similar to one of the problems RISC-V is having, though at least they pretend to care).

masklinn 3y ago
Also “notoriously weak” memory model even as multithreading was taking off, and > The processor may lose track of your LDx_L if you perform any memory access other than a matching STx_C, or if you perform a branch instruction, or if you trigger a trap (such as executing an emulated instruction), or if you execute more than 20 instructions after the LDx_L. (LDxL and STxC are locked load and conditional store)
- colejohnson66 3y ago
  What do you mean “lose track of”?
  - masklinn 3y ago
    Discard / clear the lock flag, so I assume the store never succeeds (but the behaviour could be less consistent).
- pm215 3y ago
  That is pretty standard for LL/SC instructions -- you'll find similar constraints on the Arm equivalent insns. In practice this doesn't matter because you only use them in a limited set of handcoded sequences to implement the atomic primitives you actually wanted, so you can always be sure that your LL/SC loop obeys the rules and makes forward progress.
  - cmrdporcupine 3y ago
    Was going to say. x86 I think has spoiled people in terms of what they expect in terms of memory model / consistency. The answer is to be careful as a dev, and hopefully let the compiler and your libraries take care of the finer details.
jabl 3y ago
IIRC they did add byte operations pretty soon after the initial generation. The memory consistency model was pretty crazy, though.

jmyeet 3y ago

Two fun facts about DEC Alpha: 1. Windows NT, which is the ancestor of modern Windows, was originally released on multiple platforms including Alpha and, I believe, MIPS; and 2. DEC, for awhile at least, had one of the most popular Web search engines: AltaVista. It wasn’t a commercial enterprise. It was mostly a technology demonstration for Alpha. For the time it was pretty good. No one at this time (the 1990s) thought there was a future in search engines. Many (including Yahoo) seemed to think curated directories were the future. Search engines were viewed as a solved problem, except by Larry Page and Sergei Brin who founded Google. The highly underrated show “Halt and Catch Fire” covers this early era of computing really well and is worth watching.

ngcc_hk 3y ago
When Windows NT and DEC is in the same message, may I suggest to mention that Windows NT is developed essentially by the DEC team.
- gbin 3y ago
  I highly recommend watching the recent interview of Dave Cutler, it gives some perspective on that https://youtu.be/xi1Lq79mLeE?si=D8_40BPga4Qj5jsW https://youtu.be/xi1Lq79mLeE?si=D8_40BPga4Qj5jsW

javitron 3y ago

Itanium was being defined around the same time the 1st Alphas came to market. By the time Itanium2 came out, it matched/surpassed the contemporary AXP parts. FWIW the alpha design teams ended up cannibalized between AMD and Intel. The original Opteron and the first generations of Core i have a ton of AXP DNA in them, from a uarch standpoint. So in a sense, Intel and AMD did continue Alpha... sort of. However. I feel that Alpha gets over fetishized on the internet sometimes. It was a clean arch, mainly because it was a clean 64bit design from the get go. But as far as uArch, it was pretty generic. Most of the uArch themes the AXP design teams used, which a lot of people think were native inventions to Alpha, came straight from industry/academia research, and plenty of other processors implemented them as well.