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A good article on CPU design

Posted: Wed Jun 01, 2016 4:13 pm
by W. H. Heydt
See: http://www.theregister.co.uk/2016/06/01/arm_cortex_a73/

The article covers a number of the design decisions that have gone into the Cortex-A73 as compared to the Cortex-A72. It is well worth reading for anyone not intimately familiar with CPU internals and why design decisions are made the way they are.

Re: A good article on CPU design

Posted: Thu Jun 02, 2016 8:55 am
by blc
I thought links to The Register were frowned up on around here :lol:

But that should be an interesting read during my lunch break.

Re: A good article on CPU design

Posted: Thu Jun 02, 2016 9:18 am
by Burngate
Interesting!

Among other things, "Whereas its predecessor, 2015's Cortex-A72, was drawn up in Austin, Texas, the new A73 microarchitecture was designed by a team in France, starting about three years ago"
Arm, whilst being Brit, went to the US for the A72, but France for this one. Apart from demonstrating a modern British lack of parochialism (to be applauded) does this have implications for the forthcoming Referendum? No foreigners need reply!

"Greenhalgh said ARM's mobile cores, even its 64-bit ones, will not drop their 32-bit (AArch32) mode for a long while because there's still plenty of apps out there that are 32-bit only"
This slightly surprised me - I would have expected it to be so straightforward to recompile an app for 64-bit that not much was still using 32-bit (apart from the Pi?) But that only shows my level of ignorance.

Re: A good article on CPU design

Posted: Thu Jun 02, 2016 10:32 am
by Heater
All 64 bit Intel processors still run in 32 bit mode. And as far as I know they still boot up in 16 bit mode. Intel has always had a big thing about backwards compatibility.

You can even run 8 bit Intel 8080 assembly language through a translator for a one to one translation of the 8 bit instructions to 16 bit instructions. Ever wonder why modern Intel processors have a DAA instruction?

There is plenty of 32 code that broke when recompiling for 64 bits. In the Linux world that mostly has been fixed. In the closed source world old binaries could be around for a long time. Companies are not interested in recompiling stuff and fixing any issues that arise.