[Ti] PowerBook "power"... or lack thereof

[Kynan Shook]

What happens if you go into the Energy Saver control panel and change 
the processor performance from the battery's default Automatic to 
Highest?  Also, check the power adapter settings; Highest is the 
default for the power adapter, but Automatic is available as well.  
Automatic is usually the best choice as far as a balance between power 
consumption and heat produced, and getting enough speed.  It usually 
works fairly well; the speed of the processor goes up and down as 
needed.  However, there seem to be certain applications that just don't 
trigger the processor to speed up appropriately, it would seem; perhaps 
ArcExplorer is one of them.  The Automatic setting will allow your 
PowerBook to automatically go between 1.25 GHz and 765 MHz.
There are other possibilities as well.  One is the amount of cache.  
The PowerBook has 512 K of L2 cache, and no L3 cache.  The PowerMac 
probably has 256 K of L2 cache and 1 MB of L3 cache.  The L3 cache 
might be just right to help speed up this particular application.  I've 
done a lot of testing with my 17" 1 GHz PowerBook (which has a 256 K L2 
and a 1 MB L3 cache), and in almost no cases does the L3 cache actually 
help performance in any measurable way.  It helps significantly if the 
L2 cache is not present; you can still retain about 80% of the speed 
gain given by the L2 cache with just the L3 cache and no L2 cache, but 
the speed difference between both L2 and L3 running and only L2 running 
is almost always miniscule.  Now, that's not always; some people have 
reported that Virtual PC, for example, runs much faster on the machines 
with this L3 cache.  Perhaps your application is another example, 
though besides VPC, I haven't heard of any others that lose significant 
speed from the change in cache.  Doubling the L2 and removing the L3 in 
almost all cases will make the computer much faster...  Unless, of 
course, you have more data to be cached than fits in 512 K (well, 
actually, it depends on cache placement policies, and where in memory 
the data is stored, and all that, but we'll ignore that).  If you're 
really curious to test this theory, you can install the optional CHUD 
tools from Apple's developer tools installer.  Among the things 
installed is a Hardware preference pane which should allow you to 
selectively enable and disable the caches on your G4, so you could see 
what it's like with no L3 cache.
On modern computers, RAM is very slow compared to the speed of the 
processor.  However, if RAM is considered slow, that makes the hard 
drive several orders of magnitude worse than glacial.  We're talking 
about the CPU waiting millions and millions and millions of cycles if 
it suddenly needs something off the hard drive.  If there is a lot of 
hard drive access (you can listen for it), that might also explain some 
of the slowdown.  The PowerBook's drive runs somewhat slower than a 
desktop drive; most PowerBooks use a 4200 RPM drive, as opposed to the 
usual desktop standards of 5400 or 7200.  This is done mostly for power 
consumption issues, but also to reduce the amount of noise produced.  
5400 RPM laptop drives are available, but they're hotter, louder, and 
will shorten your battery life.  One advantage of laptop drives is that 
the data must be packed into a smaller space on the hard drive, so even 
though the drive is spinning more slowly, often the data is passing 
under the heads at nearly the same speed (the heads cover less area in 
a specific amount of time, but the bit density is often significantly 
higher in the smaller drives).  However, it could be a contributing 
factor.

Anyway, that should give you a few ideas on what could influence the 
speeds...  Hope your brain didn't explode there!

Chris Olson <chris at astcomm.net> writes:
> Background info:
> 1.25 Ghz G4 AlBook w/1.0 GB RAM.
> I'm working with ESRI shapefiles in ArcExplorer.  Polygon files seem to
> render pretty quickly, however, point data files are very slow.  Some
> of the point files I'm working with have ~148,000 data points within a
> few minutes of latitude/longitude.  It'll take the PowerBook up to 30
> seconds to render a file, and every time you do a query on an
> underlying layer, it has to re-render the map, which is time consuming
> and quite slow.
>
> Taking the same project to my single processor 1.25 Ghz G4 Power Mac
> (1.0 GB 333 Mhz DDR SDRAM)  is a dramatic difference.  The same file
> that takes 30 seconds on the PowerBook takes less than 5 seconds on the
> Power Mac.  Video RAM is the same - 64 MB, although the Power Mac has
> an ATI Radeon 9000 and the PB has an ATI Radeon 9600 mobility.  I don't
> think it's a video issue - I believe it's a difference in processor
> power.
>
> Any reason for this?  Anybody else work with ArcExplorer on a
> PowerBook?  I'd be happy to zip up and send a dataset and project file
> for somebody with experience to try for curiosity's sake.