Re: Streams in Ada

[Robert A Duff <bobduff@world.std.com>]

Florian Weimer <fw@deneb.enyo.de> writes:

> "Marin David Condic" <marin.condic.auntie.spam@pacemicro.com> writes:
> 
> > I suppose that may be what it would be if you thought of the *LARGEST*
> > addressable unit - but going the other direction is I think what was
> > intended.
> 
> No, the smallest unit which ordinarily hits the memory bus on the
> message I'm typing is 32 octets -- a cache line. ;-)
> 
> > AFAIK, Alphas will address a single byte
> 
> In standardeese, you're correct (a byte is commonly defined as the
> smallest addressable storage unit),

Perhaps nowadays, but in the old days, that wasn't true.  People talked
about "byte addressable", meaning you can address bytes (whatever that
means -- 8 bits?  something smaller than a word?).

>... but if you mean a single octet,
> I don't think so, AFAIK, the original Alpha CPU doesn't have this
> feature.  (Modern CPUs which also can operate in a PC-like environment
> probably have octet) Can anyone shed some light on this issue?

An address on the Alpha points to a single octet (8-bit byte).  The
original Alpha had no instructions for loading a byte, but I would still
call it an "addressable unit".  So on Alpha, an Ada compiler ought to
define:

    Storage_Unit = 8
    Word_Size = 64

- Bob