[fpc-devel] Re: System 370: Episode 3. Addressing and it's limits Part One!

steve smithers stevie at collector.org
Fri Feb 10 20:06:08 CET 2012

> Mark Morgan Lloyd wrote on Fri, 10 Feb 2012 09:22:22 +0000
> In any event, I'd not expect somebody who'd spent their career focussed 
> on mainframes to be sufficiently familiar with x86 assembler to be able 
> to make informed criticism at this level of detail. Similarly I'd not 
> expect somebody who'd spent their career focussed on PCs to be able to 
> make informed criticism of mainframe I/O architecture and the claimed 
> throughput levels.

It's not either / or.  Just because someone is fluent in IBM Assembler,
has no influence on the fluency in other assembly languages.  I've had
a PC at home for 20 years, plenty of time to become familiar with x86
assembler;  I just haven't had the inclination since I discovered Turbo
Pascal.  In fact I would suggest that knowing IBM Assembler would be a
great help in learning x86 assembler, or any other assembler come to that.
> Mark Morgan Lloyd Fri, 10 Feb 2012 09:33:03 +0000
> > Thirdly, it should be noted here that if the intention is to provide support on
> > Hercules based systems, that Hercules allows us to use the newer instructions
> > introduced by the processor upgrades even though we are using processors that
> > shouldn't, in theory, support them.
> If Hercules is configured as an S/390 to keep the guest operating system 
> (e.g. Linux) happy, is it possible to validate that a binary is 
> completely safe to run on an S/370, i.e. contains no 390-specific features?

I'm not exactly clear on what you are asking.  You could turn off the 390
features on Hercules and see if it crashes, or you could ensure you don't
generate thme by using some compiler switch, or you could remove the macros
required for the IBM Assembler to support the mods, they will cause assembly
errors.  Or what ...?
> > This doesn't apply to providing 31 or 64 bit
> > addressing however, as considerable operating system support is required to
> > handle these modes.
> Although the OS/380 project appears to have made major progress on this.
OS/380 IS the operating system support.  But it only supports 31 bit addressing
using some custom enhancements to both Hercules and MVS 3.8.

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