[Info-vax] OpenVMS I64 V8.1 "Evaluation Release"?

[glen herrmannsfeldt]

Dennis Grevenstein <dennis.grevenstein at gmail.com> wrote:

(snip, someone wrote)
>>> I sometimes wonder what might have happened if AMD
>>> had not come up with x86_64.
 
>> That's like speculating how history would have developped 
>> in a parallel universe.

> Sure, but IA64 had a chance to take over serious x86 market share,
> because the old x86 was only a 32bit platform.

Yes, but how many really need 64 bits? How many computers sold
today have more than 4GB of RAM? 

Much of high-end scientific computing has been made affordable
by people buying processors that they didn't need, driving the
economy of scale. 

Even more, IA32 with a segment descirptor cache would have allowed
addressing over 4GB pretty easily. While some programs do need more
than 4GB, not so many need so much in one contiguous addressable block.
The IA32 MMU doesn't allow for more than 4GB (mistake one), and, 
without a descriptor cache the overhead of loading segment descriptors
would slow down large model 32 bit code way too much.

The small number of registers in IA32 was also a problem, and
x86_64 does help there. That might have been fixed without going
to 64 bits, though.

> I'm not saying that VMS would be much more popular. I'm just
> saying that it wasn't nessecarily a bad idea to get into the IA64
> market back then.

For the real high-end servers that really need the large address
space, IA64 might not have been so bad, but it seems to me that it
took too long to get to market, partly because of the need for IA32
compatibility. 

-- glen