Subject: Re: True 64bit OS ?
To: None <email@example.com>
From: Jonathan Stone <jonathan@DSG.Stanford.EDU>
Date: 07/07/1997 14:46:42
Ted Lemon writes:
>> I'm writing some info about NetBSD to my WWW page and am in tempting
>> to say NetBSD is true 64-bit on 64-bit architectures. Is this
>> statement true ? I feel the sentence "true 64-bit" a bit vague ;-)
>> What does it mean anyway besides ability to address more memory ?
>I think this is not such a great idea - it's sort of like bragging
>that a car is a True Vehicle. The Alpha is a 64-bit-only
>architecture, so anything that runs on the Alpha is by definition a
>64-bit OS. This isn't a selling point, so why bring it up?
Err, NT on Alpha is limited to 32-bit addressing. It does use 64-bit
>The only platform I know of where this distinction might be
>interesting is the MIPS R4000 and later processers, which actually
>have 32- and 64-bit modes.
Mips CPUS (mips3 and newer) are even more complicated...
The FPU has a mode bit that says whether FPU registers are 32 or 64
bits. IEEE doubles always use 64 bits, but in 32-bit mode they use a
register pair. 64-bit FPU mode can be turned on even when the integer
CPU is used in 32-bit mode, and GCC has an option to generate code
that uses this feature.
Support for 64-bit FPU (not integer!) registers _may_ get added for
NetBSD 1.3. AFAIK, it's just allowing that bit to be set from
userspace, and doubling the size of the FPU context and FPU state in
I haven't even begun to look at either using 64-bit integer registers
in a 32-bit address space. TLB support for 64-bit virtual addresses.
>Maybe Jonathan Stone or Per Fogelstrom
>can speak to the state of the implementation on those CPUs...
NetBSD is still purely 32-bit mode. I beleive OpenBSD is also, but
anyone who cares should really ask Per.