On 10/29/24 04:49, Philip Guenther wrote: > On Mon, Oct 28, 2024 at 11:43 AM Christian Schulte <c...@schulte.it> wrote: > ... >> I would really like to understand why this architecture stood the test >> of time. Just because it boots in 8 bit CPU mode from the 70ties not >> even capable of beating a 6502? > <...> > > Building a base of users with computers capable of running a more > powerful ISA/OS/whatever (while it still supports their existing > applications), so that application writers believe that there will be > sufficient user base with that capability to use software written to > use that power, which drives more people to get those more capable > computers, has been a huge driver of not just the evolution of x86 but > of the computer industry as a whole. x86 made those steps easy for a > line of ISA evolution; Apple went a different direction and put the > backwards/forwards compat into their build tools so you could build on > one arch/OS-version and move to a different one and did that so well > that they managed to move user bases from m68k to powerpc to x86 to > arm64 with compat across each transition. You _do_ understand that > the set of people who can rebuild all the software they directly use > is *tiny* and the subset of those for whom doing so is a net positive > use of the limited time they have between birth is death is > insubstantial, yes? > > For Linus's thoughts on the amd64 transition, consider > https://yarchive.net/comp/amd64.html
He is more or less speaking about transitioning from 32bit to 64bit in general there. Of course for someone having e.g. a Windows installation on a hard disk, being able to just replace a e.g. broken mainboard with a new one and being able to just boot the existing installation with that without having to re-install everything may be of great value. Is that really required and justifies backwards compatibility for more than 4 decades? You could run e.g. DOS on a smartphone these days, for example. No need for the CPU to support all those obsolete modes. What do I know? It is, what it is. So I just need to deal with it. > > > If the above doesn't have you going "I see how others could value > something that I found inscrutable" then I don't think I can help you > any further in that understanding. > > > Philip Guenther Maybe I am just failing the definition of "general purpose" those not so general purpose registers and instructions are called. Who knows? Maybe it's just brilliant to need to know what instructions can be used with what registers and what addressing modes. I read everything from mbr to init_x86_64(paddr_t first_avail) without committing suicide so far. -- Christian
