5 ms·

The 64bit Aarch64 ISA has very little in common with the original ISA from '85.

by stsquad 5y ago

vanderZwan 5y ago
It makes about as much sense as calling humans "lactating fish"
- deleted 5y ago
  [deleted]
- mumblemumble 5y ago
  Where the category "fish" isn't a clade - it's possible to evolve to no longer be a fish - it's more comparable to a specific generation of ARM chips, like perhaps ARM32, than it is to the ARM line in general. It would be weird to say "64-bit ARMv5" in the same way that it would be weird to say "lactating fish". But it is not weird to say "64-bit ARM" for the same reason it isn't weird to say "lactating euteleostome."
  - tekproxy 5y ago
    While this is a better analogy and worth reading, "fish" is funnier.
  - vanderZwan 5y ago
    I appreciate that you used my bad joke as a fact-checking opportunity to spread some scientific knowledge :)
    - birdyrooster 5y ago
      We take our analogies very seriously here, no jokes sir.
  - aYsY4dDQ2NrcNzA 5y ago
    You guys are going to have to eat these words when fishermen off the coast of Madagascar pull up an example of Pisces lactatus.
    - vanderZwan 5y ago
      Is that the scientific designation of mermaid fantasies of lonely fishermen?
mumblemumble 5y ago
I gather that it's true that ARM hasn't been as good about backwards compatibility as some of its competitors, but was ARMv8 really so much of a jump from ARMv7 that one can't count it as part of the same line of processors anymore?
- als0 5y ago
  It is a jump. There is plenty to dislike about ARMv7.
- saati 5y ago
  The v7->v8 jump was the biggest one in the history of ARM, it's totally redesigned, they only kept the name.
  - mumblemumble 5y ago
    Well, that and the ability to run v7 code if you switch it into aarch32 mode. So one could be forgiven, I should think, for thinking the shift was more comparable to x86 -> amd64 than it was to x86 -> ia64.
- leeter 5y ago
  They weren't horrible either, AArch64 is incompatible with AArch32 but you can still implement both on the same chip with shared internals. AMD didn't have to extend x86 the way they did, but without buy in from intel there was no way forward unless they went the route they did. Because unless both had agreed to shift to UEFI at the same time and agreed on an ISA it wasn't going to happen. This is why even a modern x86-64 processor has to boot up in real mode... because there was no guarantee that the x64 extensions were going to take off, so AMD had to maintain that strict compatibility to be competitive. AArch64 had no prohibition, because there is no universal boot protocol for ARM. Insofar as the UEFI or loader sets the CPU in a state the OS can use then it's fine. The fact that there is one IP holder helped as well. That said could AMD make a x86-64 processor without real mode or compatibility mode support? Yes they can. In fact I would hope that the processors they ship to console manufacturers fit that bill. There is a lot they could strip out if they only intend to support x86-64.

The 64bit Aarch64 ISA has very little in common with the original ISA from '85.

vanderZwan 5y ago

It makes about as much sense as calling humans "lactating fish"

deleted 5y ago
[deleted]
mumblemumble 5y ago
Where the category "fish" isn't a clade - it's possible to evolve to no longer be a fish - it's more comparable to a specific generation of ARM chips, like perhaps ARM32, than it is to the ARM line in general. It would be weird to say "64-bit ARMv5" in the same way that it would be weird to say "lactating fish". But it is not weird to say "64-bit ARM" for the same reason it isn't weird to say "lactating euteleostome."
- tekproxy 5y ago
  While this is a better analogy and worth reading, "fish" is funnier.
- vanderZwan 5y ago
  I appreciate that you used my bad joke as a fact-checking opportunity to spread some scientific knowledge :)
  - birdyrooster 5y ago
    We take our analogies very seriously here, no jokes sir.
- aYsY4dDQ2NrcNzA 5y ago
  You guys are going to have to eat these words when fishermen off the coast of Madagascar pull up an example of Pisces lactatus.
  - vanderZwan 5y ago
    Is that the scientific designation of mermaid fantasies of lonely fishermen?

mumblemumble 5y ago

I gather that it's true that ARM hasn't been as good about backwards compatibility as some of its competitors, but was ARMv8 really so much of a jump from ARMv7 that one can't count it as part of the same line of processors anymore?

als0 5y ago
It is a jump. There is plenty to dislike about ARMv7.
saati 5y ago
The v7->v8 jump was the biggest one in the history of ARM, it's totally redesigned, they only kept the name.
- mumblemumble 5y ago
  Well, that and the ability to run v7 code if you switch it into aarch32 mode. So one could be forgiven, I should think, for thinking the shift was more comparable to x86 -> amd64 than it was to x86 -> ia64.
leeter 5y ago
They weren't horrible either, AArch64 is incompatible with AArch32 but you can still implement both on the same chip with shared internals. AMD didn't have to extend x86 the way they did, but without buy in from intel there was no way forward unless they went the route they did. Because unless both had agreed to shift to UEFI at the same time and agreed on an ISA it wasn't going to happen. This is why even a modern x86-64 processor has to boot up in real mode... because there was no guarantee that the x64 extensions were going to take off, so AMD had to maintain that strict compatibility to be competitive. AArch64 had no prohibition, because there is no universal boot protocol for ARM. Insofar as the UEFI or loader sets the CPU in a state the OS can use then it's fine. The fact that there is one IP holder helped as well. That said could AMD make a x86-64 processor without real mode or compatibility mode support? Yes they can. In fact I would hope that the processors they ship to console manufacturers fit that bill. There is a lot they could strip out if they only intend to support x86-64.