[Info-vax] Microsoft: Alpha architecture responsible for poor Windows file compression

[Stephen Hoffman]

On 2016-11-02 17:04:26 +0000, johnwallace4 at yahoo.co.uk said:

> I'm not an Alpha architecture expert, but I used be familiar with the 
> Alpha Architecture Handbook...

The folks at Microsoft are very referring to the Alpha systems that 
lacked the byte-word extension in the Alpha microprocessor.

EV56 and later had byte-word.   EV5 and earlier Alpha microprocessors didn't.

This caused more than a little grief even for OpenVMS, and particularly 
in I/O space, and led to some complex software designs.

With byte-word support, Alpha systems after the Rawhide family — after 
the AlphaServer 4100 series and derivatives — avoided the need for 
swizzle-space and other "fun" required on earlier systems.

http://labs.hoffmanlabs.com/node/543

The lack of byte-word also effected the compiler code generation — code 
generated by Alpha compilers variously included effectively-parallel 
code paths, with specific instructions generated and later selected at 
run-time by branching based on Alpha microprocessor, to select the 
specific code path appropriate for the current Alpha processor — and 
also effected algorithm choices and other related details.

http://h41379.www4.hpe.com/wizard/swdev/alpha_implver_amask_features.c

In short, I can easily see these details effecting the selection of a 
compression algorithm.  Though not necessarily keeping the original old 
compression algorithm around — as the primary or default choice for 
newly-initialized disk volumes — long after Windows was de-supported on 
Alpha.


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