wow, you both did a good job , I asked lots of people and they did't say very clear, it suddenly enlightened me, thanks all.
On 26 November 2010 22:32, Alan McKinnon <alan.mckin...@gmail.com> wrote: > Apparently, though unproven, at 16:09 on Friday 26 November 2010, Stroller > did > opine thusly: > > > On 26/11/2010, at 6:07am, sam new wrote: > > > Thanks all, I have a question , when we build the system, always use > host > > > client to build the toolchain , then GCC Glibc ...kernel some unity ... > > > from source ,but where the frist system come from ,does it build using > > > the Assembly language or machine language? I mean just give you X86 > > > hardware and power , no OS, no livd cd . I am afraid it is out of this > > > topic.but it always puzzled me :-) > > > > I think you want to know which came first - the chicken or the egg? > > > > For a few years, operating systems were indeed written in assembler. > Then, > > c 1970, Unix was the first operating system written in a higher-level > > programming language, C. Likewise, I guess, the first compilers would be > > written in assembler, until one was written that could compile itself and > > become "self-hosting". > > > > Thus new compilers and operating systems can now be written in > higher-level > > languages (although C isn't very high-level) and compiled using an > > existing compiler. > > > > That Unix was written in C is what has lead to its ubiquity - until then > > every different brand of computer had its own operating system, usually > > written by the manufacturer. Written in assembly, these were > non-portable. > > Writing the operating system in C allowed it to be ported to different > > hardware architectures, and programs could be written that would run on > > all the different systems out there (as long as those ran Unix). > > > > Linux was written on a Minix system, Minix was written c 1987 and so > might > > have been written on one of the BSDs that was around then; the BSDs were > > probably written on an AT&T Unix. > > > > When Intel produce a new chip - or gcc wants to support a new > architecture > > - they rewrite the compiler (the "backend" part of it) to output machine > > code to suit the new chip's instruction set (which will be different from > > that of other chips - PPC vs ARM vs MIPS vs x86). The compiled code is > > then transferred to the new machine and fingers are crossed as everyone > > waits to see if it boots. > > > > http://en.wikipedia.org/wiki/History_of_Unix > > http://en.wikipedia.org/wiki/Compiler > > > > Stroller. > > One could ask the question "where did the first assembler come from?" > > Just as the first OSes and compilers were written in assembler to bootstrap > C, > so the first assemblers were written in hex codes to bootstrap the > assembler. > But hex code editors ran software, so where did the first hex code input > gadget come from? > > And the answer to that is that it was written in binary. Yes that's right - > a > panel with 16 toggle switches and a few pushbuttons. Those didn't require > software as everything was implemented in hardware. > > So now you know :-) > > > -- > alan dot mckinnon at gmail dot com > >
