Immutability - was Re: ENIAC programming Was: release dates of early microcomputer operating systems, incl. Intel ISIS

[dwight]

> Date: Thu, 17 Sep 2015 13:29:34 -0400
> From: toby at telegraphics.com.au
> To: General at classiccmp.org; classiccmp.org:On-Topic and Off-Topic Posts cctalk at classiccmp.org; General at classiccmp.org
> Subject: Immutability - was Re: ENIAC programming Was: release dates of early microcomputer operating systems, incl. Intel ISIS
> 
> On 2015-09-17 12:44 PM, Jon Elson wrote:
> >
> >>      > From: Dave Wade
> >>
> >>
> >>      > to me a "computer" without self-modifying code is a programmable
> >>      > calculator even if it has index registers...
> >>
> >>
> > Most modern computer languages run with the executable instructions in a
> > "pure code" section, which is set to be NOT writeable by the program.
> > This avoids a LOT of simple mistakes and REALLY hard to find program
> > crashes.
> > This is true of MS, Linux/Unix and the VMS program environment that I
> > have used for about 40 years.  I think you have to go back to maybe
> > Windows 95 or RT-11 to not have that protection.
> 
> Modern languages extend this "protection" further, to the programmer 
> model, with immutable bindings and data structures, shunning variables 
> entirely.
> 
> --Toby
> 
> >
> > Jon
> >
> 

If working on a newer X86 processor, this is necessary, not to protect the
code but because the code is cashed and my not be updated in time for
it to be executed.
Write through is expensive and only provided on the data side, if at all.
Dwight