On Thu, Jul 28, 2016 at 12:22:23PM -0400, Alan Corey wrote: > Huh? I thought they claimed they were interchangeable. I had an > image from my model B days 3 years ago that I booted on my 3B. And I > cloned a working current 3B SD card and booted a Zero from it. There > isn't a different Debian image for every brand of motherboard and CPU, > they probe to see what hardware is there. I wouldn't expect older > images to contain drivers for newer hardware maybe. > > I guess I wouldn't make too much of the jump to 64 bit just yet. I > remember when i386 jumped to 32 bit. 16 bit had a messy segmented > memory addressing scheme I was glad to get away from. I can't afford > more than 32 bits worth of RAM anyway, especially since I've usually > got about 4 machines running.
Well it isn't actually just a question of memory (most 8bit CPUs had 16 bit address space, and many 16 bit CPUs had 24 or 32 bit address space, and some 32 bit x86 and arm chips can do 36 or 40 bit address space physically). What you often gain going to a 64 bit CPU is the ability to do 64 bit arithmetic in one instruction, and store the variables in one register rather than two, rather than a bunch of stuff the compiler generates for you. After all if you take two 64 bit integrs and try to multiply them on a 32 bit CPU, most of the time you end up with numerous multiply, shift, add, mask, instructions to implement the calculation using 32 bit only instructions, while on a 64 bit CPU usually it is just one instruction. So the 64 bit CPU will probably do the calculation faster than the 32 bit CPU. Of course if you only need 32 bit calculations, then it doesn't matter, so in many cases it isn't an issue, but when it matters it can really make a difference in performance. -- Len Sorensen
