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I would very much like to see ARM gain traction in the desktop market: the whole way the x86 works is quite inelegant (longer instructions decoded into a RISC-l

by TheBoff 15y ago

I would very much like to see ARM gain traction in the desktop market: the whole way the x86 works is quite inelegant (longer instructions decoded into a RISC-like 'microops'). Considering how small ARM is compared with Intel, they've done a fairly fantastic job.

ikono 15y ago
Is one actually better than the other? I know very little about these things but it seems like ARM relies on a higher volume of simpler instructions at a faster clock rate vs x86 which uses fewer, larger, more complex instructions which take longer to execute. Don't you eventually get to a point where the only way to increase performance is to use more complex instructions? I mean at some point Intel will be able to deliver x86 CPUs in ultra low power form factors. At the same time ARM CPUs will become increasingly powerful. Is it clear to those that understand these things that one architecture is going to be inherently better?
- sliverstorm 15y ago
  RISC vs. CISC boils down to CPU Designers vs. Compiler in terms of where the low level optimization happens. One of the big arguments for RISC, as I am familiar with it, is that it allows the entire processor team to focus on making just a few instructions as fast as physically possible, rather than dealing with the truckload of instructions we have in a modern CISC processor. Or, perhaps in the ARM case, as efficient as physically possible.
- TheBoff 15y ago
  This was only true some time ago, unfortunately. The technique used by both companies to achieve speed increases is called 'pipelining', which essentially means you can have a different instruction in each bit of the processor (so, the ALU, the instruction fetch, the memory unit are all doing different instructions). The problem with this is that pipelining only works on instructions that have a very regular format, and run in a similar number of clock cycles, and the only way to keep instructions heterogeneous is to not have very many of them! Intel, however, supports a massive instruction set, with some hugely complex instruction. They do this by actually "compiling" their complex instructions on the chip to a format which looks a lot like ARM instructions, which they call micro-ops. I would say that the ARM architecture is inherently better, because it does not waste all this silicon to do instruction translating, and you know exactly what is being executed on the processor, simplifying the job of the hardware designer, and allowing them to focus solely on performance (/power consumption/whatever), and allowing compilers to do instruction level fine tuning.
- yason 15y ago
  Practically x86 processors since a few generations back have been internally running on a smaller RISC-like microcode core. The x86 layer is there mostly for the dreaded compatibility (and to prevent compilers from optimizing directly into any RISC code ;))
  - ikono 15y ago
    Is Intel's microcode core better than other competing RISC cores? Is it really that Intel's process is that much better? It seems like it's unanimously the best, but it can't explain everything can it? I'm having a hard time wrapping my mind around this. It almost feels like Intel has simply added a layer of abstraction. It isn't clear to me that this is a bad thing. Intel has the flexibility of changing that microcode core as they please without worrying about the need for everything to be recompiled if they think of a better implementation with a different instruction set. For very specialized low power devices ARM makes sense. For more complex systems I'm not so sure. You see a strong movement in software towards increasing levels of abstraction. Why would hardware be different? Is that a fair assessment of the situation? Or am I missing something?
DarkShikari 15y ago
(longer instructions decoded into a RISC-like 'microops'). The thing is, in practice, this hasn't been true since 1985. Nobody actually uses the legacy instructions that are "decoded into RISC-like microops" except people writing 4K demos. In reality, ARM instructions are actually longer on average, and more complex on average. Nor is this a bad thing: it means that ARM IPC is more valuable than x86 IPC. ARM's advantage is that their instructions are longer, more complex, and easier to decode: not that they're "simpler and more RISC-like". RISC, at least in its original sense, is as dead as a doornail.
- ikono 15y ago
  What's Intel's advantage(aside from process)? And why hasn't there been a competitive ARM chip in the high performance market?
  - DarkShikari 15y ago
    Intel's advantage: 1. Decades of experience, smart people, and good chip design. 2. Making a chip with Core i7-like power is hard, even an ARM. It'd probably be a totally new experience for most ARM chip designers, very expensive, and it might not even sell.

by TheBoff 15y ago

ikono 15y ago

Is one actually better than the other? I know very little about these things but it seems like ARM relies on a higher volume of simpler instructions at a faster clock rate vs x86 which uses fewer, larger, more complex instructions which take longer to execute. Don't you eventually get to a point where the only way to increase performance is to use more complex instructions? I mean at some point Intel will be able to deliver x86 CPUs in ultra low power form factors. At the same time ARM CPUs will become increasingly powerful. Is it clear to those that understand these things that one architecture is going to be inherently better?

sliverstorm 15y ago
RISC vs. CISC boils down to CPU Designers vs. Compiler in terms of where the low level optimization happens. One of the big arguments for RISC, as I am familiar with it, is that it allows the entire processor team to focus on making just a few instructions as fast as physically possible, rather than dealing with the truckload of instructions we have in a modern CISC processor. Or, perhaps in the ARM case, as efficient as physically possible.
TheBoff 15y ago
This was only true some time ago, unfortunately. The technique used by both companies to achieve speed increases is called 'pipelining', which essentially means you can have a different instruction in each bit of the processor (so, the ALU, the instruction fetch, the memory unit are all doing different instructions). The problem with this is that pipelining only works on instructions that have a very regular format, and run in a similar number of clock cycles, and the only way to keep instructions heterogeneous is to not have very many of them! Intel, however, supports a massive instruction set, with some hugely complex instruction. They do this by actually "compiling" their complex instructions on the chip to a format which looks a lot like ARM instructions, which they call micro-ops. I would say that the ARM architecture is inherently better, because it does not waste all this silicon to do instruction translating, and you know exactly what is being executed on the processor, simplifying the job of the hardware designer, and allowing them to focus solely on performance (/power consumption/whatever), and allowing compilers to do instruction level fine tuning.
yason 15y ago
Practically x86 processors since a few generations back have been internally running on a smaller RISC-like microcode core. The x86 layer is there mostly for the dreaded compatibility (and to prevent compilers from optimizing directly into any RISC code ;))
- ikono 15y ago
  Is Intel's microcode core better than other competing RISC cores? Is it really that Intel's process is that much better? It seems like it's unanimously the best, but it can't explain everything can it? I'm having a hard time wrapping my mind around this. It almost feels like Intel has simply added a layer of abstraction. It isn't clear to me that this is a bad thing. Intel has the flexibility of changing that microcode core as they please without worrying about the need for everything to be recompiled if they think of a better implementation with a different instruction set. For very specialized low power devices ARM makes sense. For more complex systems I'm not so sure. You see a strong movement in software towards increasing levels of abstraction. Why would hardware be different? Is that a fair assessment of the situation? Or am I missing something?

DarkShikari 15y ago

(longer instructions decoded into a RISC-like 'microops'). The thing is, in practice, this hasn't been true since 1985. Nobody actually uses the legacy instructions that are "decoded into RISC-like microops" except people writing 4K demos. In reality, ARM instructions are actually longer on average, and more complex on average. Nor is this a bad thing: it means that ARM IPC is more valuable than x86 IPC. ARM's advantage is that their instructions are longer, more complex, and easier to decode: not that they're "simpler and more RISC-like". RISC, at least in its original sense, is as dead as a doornail.

ikono 15y ago
What's Intel's advantage(aside from process)? And why hasn't there been a competitive ARM chip in the high performance market?
- DarkShikari 15y ago
  Intel's advantage: 1. Decades of experience, smart people, and good chip design. 2. Making a chip with Core i7-like power is hard, even an ARM. It'd probably be a totally new experience for most ARM chip designers, very expensive, and it might not even sell.