64-bit or 32-bit: When will it matter?

David Schwartz,
Can you answer a few questions please?

1. Just so I know, what exactly is PAE? (yes, I know what it stands for)

2. What does it do?

3. Why is it a bad workaround?

4. How much RAM can Win 9x, Win NT, 2K and XP, Mac OS 8, 9 and X, and other *nix (assuming
most popular distros) handle without using this "PAE workaround"?

I'm asking these because there are quite a few things I'd never heard of in Brendan's post.

Cool_X

David Schwartz wrote:
"Brendan Trotter" wrote in message
...


"David Schwartz" wrote in message
...


Right, and that will be the case with 32-bit systems in about three
years as people want to put more than 2Gb (and then more than 4Gb) of
memory
in their systems.


I think you're missing the difference between "physical addresses"
and "virtual addresses", and the difference between architectural
design and CPU implementation.


No, I'm not missing anything. What you said has nothing whatsoever to do
with what I said. It's *possible* to address an unlimited amount of memory
with an 8-bit CPU, but nobody does that if they don't have to. As soon as
the majority of computers are 64-bit capable, they won't have to, and so
they won't. In any event, the shortage of virtual addresses is the more
serious problem.

PAE is an ugly workaround. A lot of people specifically purchase the
maximum amount of memory their OS can handle without PAE because they want
to avoid it.

DS

Look here.

http://www.microsoft.com/whdc/system...AE/pae_os.mspx




"Cool_X" wrote in message
news:GAqqe.1641154$Xk.437144@pd7tw3no...
David Schwartz,
Can you answer a few questions please?

1. Just so I know, what exactly is PAE? (yes, I know what it stands for)

2. What does it do?

3. Why is it a bad workaround?

4. How much RAM can Win 9x, Win NT, 2K and XP, Mac OS 8, 9 and X, and
other *nix (assuming most popular distros) handle without using this "PAE
workaround"?

I'm asking these because there are quite a few things I'd never heard of
in Brendan's post.

Cool_X

David Schwartz wrote:
"Brendan Trotter" wrote in message
...


"David Schwartz" wrote in message
...


Right, and that will be the case with 32-bit systems in about three
years as people want to put more than 2Gb (and then more than 4Gb) of
memory
in their systems.


I think you're missing the difference between "physical addresses"
and "virtual addresses", and the difference between architectural
design and CPU implementation.


No, I'm not missing anything. What you said has nothing whatsoever to
do with what I said. It's *possible* to address an unlimited amount of
memory with an 8-bit CPU, but nobody does that if they don't have to. As
soon as the majority of computers are 64-bit capable, they won't have to,
and so they won't. In any event, the shortage of virtual addresses is the
more serious problem.

PAE is an ugly workaround. A lot of people specifically purchase the
maximum amount of memory their OS can handle without PAE because they
want to avoid it.

DS

"Cool_X" wrote in message
news:GAqqe.1641154$Xk.437144@pd7tw3no...

David Schwartz,
Can you answer a few questions please?

Sure.

1. Just so I know, what exactly is PAE? (yes, I know what it stands for)

PAE allows an x86 processor to access more physical memory than it can
address with 32-bits. Specifically, it allows 36-bit *physical* address.

2. What does it do?

It basically adds an extra 4-bits in the page table mappings.

3. Why is it a bad workaround?

Because it doesn't increase the address space seen by a process. Because
it's a workaround rather than a real solution.

4. How much RAM can Win 9x, Win NT, 2K and XP, Mac OS 8, 9 and X, and
other *nix (assuming most popular distros) handle without using this "PAE
workaround"?

I'm asking these because there are quite a few things I'd never heard of
in Brendan's post.

Typically about 3Gb.

If you're looking for more specific information, use a search engine. It
would take many dozens of pages to answer your questions in detail because
they're not very specific.

DS

It does seem EVERYTIME there is a shift in the CPU for PCs, we have this
same discussion. Only servers need it. Only workstations need it.
Only hard core gamers need it. Only power users need it. Only...oh,
its required. I remember the shift from the 8088 to the 8086..who needs
16 "real" bits??? 8086 to 80286....20 bit memory access?? what do I
need with 16 MB of RAM??? then the 80386...who needs 32 bit registers,
we still run DOS....and so on....

Hi,

"David Schwartz" wrote in message
...
PAE is an ugly workaround. A lot of people specifically purchase the
maximum amount of memory their OS can handle without PAE because they want
to avoid it.

I found PAE to be a fairly elegant extension, except for CR3 (the page
directory pointer table address) being restricted to 32 bits instead of
being extended to 36 bits like the rest of the paging system - a minor
hassle for an OS's memory manager considering that it needs to
differentiate between 20 bit physical address (for ISA DMA), 32 bit
physical addresses (for 32 bit PCI devices) and 36 bit physical addresses
anyway.

The only other relevant issue is the overhead of PAE paging structures,
which consumes roughly twice the amount of memory as an equivelent
32 bit paging system when operating on 4 KB pages, and roughly 4 times
the memory when operating with PSE (4 MB or 2 MB page sizes).

Please note that the lower level paging structures (page directories and
page tables) are identical for both 64 bit paging and PAE. To handle the
higher 32 bits of a 64 bit linear address the PDPT (page directory pointer
table) was extended from 32 entries to 512 entries, and a new top level
table was added (the PML4E). Considering that the only real differences
were needed to support 64 bit linear addressing, and that AMD left the
remainder unchanged, I'd say Intel's PAE "work-around" was quite good.

I can understand people trying to avoid installing 4 GB or more of RAM,
but I'd suggest this has more to do with things like 32 bit PCI devices
using bus mastering in conjunction with buggy/old device drivers rather
than PAE itself (ie. any mechanism that supported physical addresses
larger than 32 bits would've caused similar problems regardless of how
good it is). This wouldn't apply to a 64 bit OS as the device drivers
all need to be updated/rewritten (and hopefully tested on computers
with 4 GB of memory).


Cheers,

Brendan

Thanks name,
I wouldn't have had time to fix that on my own.

Cool_X

name wrote:
Look here.

http://www.microsoft.com/whdc/system...AE/pae_os.mspx




"Cool_X" wrote in message
news:GAqqe.1641154$Xk.437144@pd7tw3no...

David Schwartz,
Can you answer a few questions please?

1. Just so I know, what exactly is PAE? (yes, I know what it stands for)

2. What does it do?

3. Why is it a bad workaround?

4. How much RAM can Win 9x, Win NT, 2K and XP, Mac OS 8, 9 and X, and
other *nix (assuming most popular distros) handle without using this "PAE
workaround"?

I'm asking these because there are quite a few things I'd never heard of
in Brendan's post.

Cool_X

David Schwartz wrote:

"Brendan Trotter" wrote in message
...



"David Schwartz" wrote in message
...


Right, and that will be the case with 32-bit systems in about three
years as people want to put more than 2Gb (and then more than 4Gb) of
memory
in their systems.


I think you're missing the difference between "physical addresses"
and "virtual addresses", and the difference between architectural
design and CPU implementation.


No, I'm not missing anything. What you said has nothing whatsoever to
do with what I said. It's *possible* to address an unlimited amount of
memory with an 8-bit CPU, but nobody does that if they don't have to. As
soon as the majority of computers are 64-bit capable, they won't have to,
and so they won't. In any event, the shortage of virtual addresses is the
more serious problem.

PAE is an ugly workaround. A lot of people specifically purchase the
maximum amount of memory their OS can handle without PAE because they
want to avoid it.

DS

I meant, I wouldn't have had time to FIND that on my own.

Sorry for the typo that I didn't catch.

Cool_X

Cool_X wrote:
Thanks name,
I wouldn't have had time to fix that on my own.

Cool_X

name wrote:

Look here.

http://www.microsoft.com/whdc/system...AE/pae_os.mspx




"Cool_X" wrote in message
news:GAqqe.1641154$Xk.437144@pd7tw3no...

David Schwartz,
Can you answer a few questions please?

1. Just so I know, what exactly is PAE? (yes, I know what it stands
for)

2. What does it do?

3. Why is it a bad workaround?

4. How much RAM can Win 9x, Win NT, 2K and XP, Mac OS 8, 9 and X,
and other *nix (assuming most popular distros) handle without using
this "PAE workaround"?

I'm asking these because there are quite a few things I'd never heard
of in Brendan's post.

Cool_X

David Schwartz wrote:

"Brendan Trotter" wrote in message
...



"David Schwartz" wrote in message
...



Right, and that will be the case with 32-bit systems in about three
years as people want to put more than 2Gb (and then more than 4Gb) of
memory
in their systems.



I think you're missing the difference between "physical addresses"
and "virtual addresses", and the difference between architectural
design and CPU implementation.



No, I'm not missing anything. What you said has nothing
whatsoever to do with what I said. It's *possible* to address an
unlimited amount of memory with an 8-bit CPU, but nobody does that
if they don't have to. As soon as the majority of computers are
64-bit capable, they won't have to, and so they won't. In any event,
the shortage of virtual addresses is the more serious problem.

PAE is an ugly workaround. A lot of people specifically purchase
the maximum amount of memory their OS can handle without PAE because
they want to avoid it.

DS

"Bill Davidsen" wrote in message
m...

Oh there were, but they were painful to use in most cases. To address your
main point, it depends on your definition of commodity software, but by
any definition I don't see that as a "killer app" justifying moving from
32 to 64 bit hardware before the old system is due for replacement.
Actually I would consider that over half of the computers in desktop use
are going to be replaced in 6-7 years, with nothing more than attrition
driving it.

Exactly. People will wind up with 64-bit capable hardware without
specifically intending to have it just through attritition. Once that
happens, software will start to be released either as 64-bit only or with
significant benefits on 64-bit platforms.

You are essentially predicting that software requirements will lag
behind hardware availability by an amount that they have never lagged
before. Ever.

I am. Based on two different justifications. The best is that there hasn't
been a 64 bit killer app for the Mac, and that's been 64 bit for a decade.
The other is that there *is* a point when people have enough and are not
willing to make an upgrade because they don't see the need.

I disagree with both points. On the first point, the 64-bitness of Macs
is not comparable to the 64-bitness of PCs for two reasons. One is that
64-bits on PCs is accompanied by other changes such as register size. The
other is that memory has now reached the point where a 32-bit limitation of
virtual memory size is significant.

As for your second point, people have been arguing that for decades and
it has never been proven right. I personally don't believe it -- people will
always want to do more and will always push their tools to the limit to
increase what they themselves can do.

If you can get access to sales info, most 32 bit systems aren't ordered
with max memory, largest disk, or fastest CPU. That certainly suggests
that people don't feel the need.

No, that's not the reason. It's because people buy for the sweet spot.
That is, the buy equipment that gives them the most bang for their buck. The
same goes for software requirements -- you can make better software if you
make the requirements greater, but you can't aim so high that no market is
left. The combination of these two forces makes 64-bit only software in six
years almost inevitable.

I'm still confident that 64 bit hardware will come driven by replacement
rather than upgrade.

I don't understand the difference between replacement and upgrade.
Perhaps you could explain. Aren't these the same things?

I agree that most computers will include 64 bit capability, but only
because it will be standard. Intel and AMD are unlikely to spend any money
in 32 bit only products, when they need more performance and lower power
foar more.

Well that's the point. As soon as the vast majority of power users are
64-bit capable, power user software will start to be released as 64-bit
only.

I predict the big 64 bit software push will be driven by greed, I mean
marketing. When enough people have gotten 64 bit hardware, Microsoft will
suddenly release new versions of all apps, with new features, and in 64
bit only. I predict they will offer *very* cheap upgrade from 32 bit
versions, because they know they will make the money on Windows-64 o/s
upgrades. But until most people have the hardware they won't push 64 bit
only, because it locks them out of a majority of the market.

Whatever.

As for gamers? I define a gamer as someone who spends at least $100 extra
on a computer for memory, faster CPU, or detter display. Oddly, that lets
out a fair percentage of people who do little else with their computer. If
they didn't spend money on hardware at 32 bits, will they jump to 64
intesad of spending the money on more games? For that matter, are the
games on the 64 bit Mac better? (real question, I have no idea)

This brings up the other flaw in your Mac example. Until a large
percentage of systems are 64-bit, there's no reason to develop software that
benefits from 64-bits.

DS

In comp.sys.intel No One wrote:
I remember the shift from the 8088 to the 8086..who needs 16 "real"
bits???

There was no "switch from the 8088 to the 8086" - very few manufacturers
ever used the 8086.

8086 to 80286....20 bit memory access?? what do I need with 16 MB of
RAM??? then the 80386...who needs 32 bit registers, we still run
DOS....and so on....

And yet both of these were enough faster than the then-available models of
the prior generation processor that people pretty much jumped at buying them
if they could afford it.

The improvements with the x86 64-bit systems aren't quite so dramatic, but
they're quite significant at least on the server side: you'd be daft to buy
a pre-Nocona Xeon-based or an Athlon MP-based server, just because Nocona
and Opteron for reasons entirely unrelated to the 64-bit-ness offer very
siginficant performance advantages over their past generations.

It's not clear to me that the same is true for the Intel 64-bit Pentium 4s,
but it also costs basically nothing to get it.

Of course, you're right... memory needs increase pretty much at a pace with
the increase of memory capacities and the decrease in memory costs... we're
only a drop or two in price away from 2gb+ on the desktop being pretty
usual, at which point 64-bit processors get a lot more attractive.

--
Nate Edel http://www.cubiclehermit.com/

"This is not a humorous signature."

Nate,
Can you please answer a few questions of mine?

1. You said:
" The improvements with the x86 64-bit systems aren't quite so dramatic, but
they're quite significant at least on the server side: you'd be daft to buy
a pre-Nocona Xeon-based or an Athlon MP-based server, just because Nocona
and Opteron for reasons entirely unrelated to the 64-bit-ness offer very
siginficant performance advantages over their past generations."

You meant that Nocona and Opteron (I've never heard of Nocona, BTW, so thanks for telling me
about it) offer "very significant performance advantages" that are "unrelated to the
64-bit-ness", on TOP of the advantages of 64-bit-ness, right? In simpler terms, Nocona and
Opteron are the best x86 server processors, right?

2. You also said:
" Of course, you're right... memory needs increase pretty much at a pace with
the increase of memory capacities and the decrease in memory costs... we're
only a drop or two in price away from 2gb+ on the desktop being pretty
usual, at which point 64-bit processors get a lot more attractive."

Are we talking about the RAM that vendors will ship STANDARD, or the RAM that buyers will
actually UPGRADE to (from the standard amount)?

3. Last but definitely not least, how will your comment in question #2 affect the laptop
world? Either by replying to my post in this thread (in comp.hardware), or by e-mail (very
much preferred, although you can do the former as well, of course!), can you give me all of
your thoughts on how everything I quoted you on in this reply will affect the laptop world?

Like I said before, if it isn't too much trouble, can you please send me an e-mail with your
response to this. That would be VERY HIGHLY appreciated.

Hope to hear from you soon!

Cool_X


Nate Edel wrote:
In comp.sys.intel No One wrote:

I remember the shift from the 8088 to the 8086..who needs 16 "real"
bits???


There was no "switch from the 8088 to the 8086" - very few manufacturers
ever used the 8086.


8086 to 80286....20 bit memory access?? what do I need with 16 MB of
RAM??? then the 80386...who needs 32 bit registers, we still run
DOS....and so on....


And yet both of these were enough faster than the then-available models of
the prior generation processor that people pretty much jumped at buying them
if they could afford it.

The improvements with the x86 64-bit systems aren't quite so dramatic, but
they're quite significant at least on the server side: you'd be daft to buy
a pre-Nocona Xeon-based or an Athlon MP-based server, just because Nocona
and Opteron for reasons entirely unrelated to the 64-bit-ness offer very
siginficant performance advantages over their past generations.

It's not clear to me that the same is true for the Intel 64-bit Pentium 4s,
but it also costs basically nothing to get it.

Of course, you're right... memory needs increase pretty much at a pace with
the increase of memory capacities and the decrease in memory costs... we're
only a drop or two in price away from 2gb+ on the desktop being pretty
usual, at which point 64-bit processors get a lot more attractive.