[samuel690069]

Can someone/ Mac Guru please help :
Power Mac G4 upgrade -- fastest processor available.
i read through all the forum similar about my question, but still very lose & can't make the right choice.. Sonnet, Powerlogix , GigaDesign or others??

My Current model
Power Mac G4 (QuickSilver 2002)
Model : M8705

Machine Model: Power Mac G4
CPU Type: PowerPC G4 (2.1)
Number Of CPUs: 1
CPU Speed: 800 MHz
L2 Cache (per CPU): 256 KB
Memory: 1.5 GB
Bus Speed: 133 MHz
Boot ROM Version: 4.3.3f2
Graphic Card ATI Radeon 9800Pro Mac Edition 256MB 4x AGP (#100-535058)
HDD Maxtor PATA 300GB 7200rpm 16MB x2pcs.

usage for :
Photoshop CS/CS2 - heavy retouching, need fast processing speed & applying lots of effects(single & Multi processor aware action).
Final cut Pro - medium to heavy video editing need fast processing speed & applying lots of effects, in DVD resolution.
Multi tasking - email/web browsing program(firefox+safari+Mail), + excel+ Phoshop CS + video editing...etc

Could someone please recommend which is the BEST/ FASTEST upgrade for my G4
for i dont have the budget to go for G5.

choice 1
PowerLogix PowerForce47 Dual G4/1.73GHz with 512K 1:1 L2 Cache ,no L3 ( #PLGPF47D1700DQ )

choice 2
Sonnet_Encore Duet 1.8GHz 512KB L2, no L3 (#SG4D-1800)

choice 3
Sonnet Encore STG4(single processor) 1.4GHz 2MB L3 (#STISG414002M)

Choice 4
GigaDesign Dual 1.8GHz G4 (7447A) 512KB L2 (#7AD-1800U )

Choice 5
PowerLogix (single processor) G4/2.0GHz 7447A PowerForce47

Choice 6
PowerLogix Dual G4/1.8GHz 7447A PowerForce47

May i know which is the fastest for my usage , some model they have L2 + L3 cache but some they have only L2 cache?

Many Thank you for your valuable time...

cheers Mac user!
samuel

[imitchellg5]

Sounds like you need a dualie. I would go for a PowerLogix Dual 1.8GHz. Whatever you do, enjoy your faster Mac

[samuel690069]

Thanks for your reply. but PowerLogix Dual 1.8GHz no longer available at OWC/ eshop macsales. what you think of Sonnet DUET 1.8GHz which don't hav L3 cache? any compare benchmark available? Thanks again
regards,
samuel

[imitchellg5]

Hmm I haven't seen any benchmarks for that but I would bet it would be still pretty fast. You could always look for the PowerLogix Dual 1.8 on eBay too.

[samuel690069]

Thanks for your advice & time..
regards,
sam

[PB2K]

I put a Powerlogix 1330 Mhz dual in my Powermac 466, it runs great. converts mp3 at a speed of about 20x

[generationfourt]

How come you don't have any OWC mercury options up there? The OWC options are great, and easier to install than the powerlogix (you don't have to run any type of cpu director). I don't know what options there are for your specific G4 but I'd look into what OWC is offering themselves. You want something with an L3 cache. A 7455 @ 1.4 L3 cache is comparable to a 1.8 L2 cache.

Check out www.xceler8yourmac.com and read the reviews of all the chips you are looking at. There are a lot of negative reviews on powerlogix. I don't mean to knock them because there are tons of people who are really happy with them as well. I would either go sonnet, gigadesigns or owc mercury extreme...

I am extremely happy with my OWC 1.4 7455 L3 cache in my sawtooth

[Lateralus]

Originally Posted by generationfourt

How come you don't have any OWC mercury options up there? The OWC options are great, and easier to install than the powerlogix (you don't have to run any type of cpu director).

PowerLogix' CPU Director software is complimentary, not required.

[PB2K]

that's right, i replaced the original CPU with the Powerlogix one and that was that.

don't try to make it difficult, its just replacing a ZIF processor !

[samuel690069]

Originally Posted by generationfourt

How come you don't have any OWC mercury options up there? The OWC options are great, and easier to install than the powerlogix (you don't have to run any type of cpu director). I don't know what options there are for your specific G4 but I'd look into what OWC is offering themselves. You want something with an L3 cache. A 7455 @ 1.4 L3 cache is comparable to a 1.8 L2 cache.

Check out www.xceler8yourmac.com and read the reviews of all the chips you are looking at. There are a lot of negative reviews on powerlogix. I don't mean to knock them because there are tons of people who are really happy with them as well. I would either go sonnet, gigadesigns or owc mercury extreme...

I am extremely happy with my OWC 1.4 7455 L3 cache in my sawtooth

thanks for yr reply..

so you said that A 7455 @ 1.4 L3 cache is comparable to a 1.8 L2 cache, in which particular application/software performance? i wil check your valueble link, thanks..
which particulr choice if you where me for the best performer upgrade(under the my work usage)?
regards,
sam

[samuel690069]

Originally Posted by PB2K

that's right, i replaced the original CPU with the Powerlogix one and that was that.

don't try to make it difficult, its just replacing a ZIF processor !

thanks for yr reply..

ZIF processor?? is better/faster then dual processor (1.8GHz 512kbL2) ?

regards,
sam

[PB2K]

zif means it's easy to replace

[samuel690069]

Originally Posted by generationfourt

How come you don't have any OWC mercury options up there? The OWC options are great, and easier to install than the powerlogix (you don't have to run any type of cpu director). I don't know what options there are for your specific G4 but I'd look into what OWC is offering themselves. You want something with an L3 cache. A 7455 @ 1.4 L3 cache is comparable to a 1.8 L2 cache.

Check out www.xceler8yourmac.com and read the reviews of all the chips you are looking at. There are a lot of negative reviews on powerlogix. I don't mean to knock them because there are tons of people who are really happy with them as well. I would either go sonnet, gigadesigns or owc mercury extreme...

I am extremely happy with my OWC 1.4 7455 L3 cache in my sawtooth

thanks for yr reply again...
i hav read all related reviews(www.xceler8yourmac.com) , but unfortunately they did not compare full products/round-up available now 2006 in the market...

Powerlogix's 7447A Dual G4/1.8GHz w/512kb L2, no L3 with Powerlogix's 7457 Dual G4/1.2GHz w/512kb L2, 2MB L3 , they are on QuickSilver G4/733..... (but they did not compare with Sonnet Dual 1.8GHz or higher GHz 7457 model and others......)

will the OWC 1.4GHz 7455 L3 cache bet all of them in terms of performance under my work uasge: multitasking, video editing, Photoshop CS ...etc??

thank you for your valueble time..
cheers Mac user,
sam

[samuel690069]

Originally Posted by PB2K

zif means it's easy to replace

thanks for yr reply...
but i still want to be sure before the heavy investment US$500-600.....
any suggestion please? Dual 1.8GHz 512kbL2 with no L3(7447A) or others low GHz with L2 & L3 together(7455, 7457)?

Thank you & warm regards,
cheers Mac user
sam

[PB2K]

my "Powerlogix 1.33Ghz Dual" comes with 2megs of level2 cache per processor. I guess it's pretty important to have lots of L1 and L2 cache.

Then, buy lots of Pc133 memory, fast 7200rpm harddisks, great videocard..just eliminate the bottlenecks

(i have a 32mb videocard heading my way, and am really eager to get all my memoryslots filled with 512mb pc133 memory) my disks are all 7200 rpm. A startup of my G4 takes about 28 seconds to get from the startupchime to the desktop. Once it has passed the grey screen it's virtually to the desktop in a second.

[Zim]

Assuming these upgrades are several hundred $$, I wonder if you aren't better off buying a dualie G4 used and selling your G4/800 (that's what I am in process of doing). My net "cost" will be ~$200-$300 once I sell the G4.

Mike

[PB2K]

what i've spent so far:
g4 466 with 512mb : 150 €
dual 1.33gHz processor upgrade : 175 € or 275 € dont remember
32mb ati nvidia videocard : 30 €

[tumbleguts]

Hello Samuel,

Caught your thread and thought I'd dispense the wisdom I've acquired having gone thru a similar experience... The Quicksilver is a mighty machine. Sure, it's no G5 - but if you optimize it correctly it can really be something that can handle most graphics / video editing programs with flare... You seemed to have already given it some pretty powerful hardware boosts - such as the Radeon 9800 Pro, some decent hard drives, and 1.5GB of memory. Off the bat - I would recommend two things:
> a dual G4 processor upgrade, and
> optimization of Hard Drives with a dedicated scratch disk.

Let me explain myself. I too have a Quicksilver. It was originally a pedestrian 733MHz - but I've since gone the whole hog and upgraded everything. I'm a graphics professional so I know what works, and what doesn't. For the kind of applications you want to use (and obviously use well) I cannot stress enough the benefit of getting a dual processor over a single. Photoshop, in particular, is one of a few programs that is fully multi-processor aware - and really struts its stuff when running on one. Overall, Mac OS X in general, is a greatly improved beast when running on a dual processor. So... if you decide to go the upgrade route - definitely gone for the dual. Cannot emphasis that enough. Regardless of speed - a dual processor will handle multitasking and processor intensive graphics applications with much more ease. And you'll really appreciate the extra grunt. (But I'll come back to the processor upgrades...)

One thing that most people often overlook when trying to maximize their machines is a correct hard drive setup. You can easily gain a 20-30% performance increase (with applications like Photoshop) by simply providing a dedicated scratch disk on a separate channel. See... the HD is really nearly always the slowest part of any computer. Ideally what you want is 3 separate drives on 3 separate bus / channels. One drive as your startup disk with Mac OS X and all your applications. One (fast) drive as a dedicated scratch disk. And another, (make it large) as your media / backup / storage / file disk. However, it's impossible to do this in a Quicksilver without adding a PCI controller - cos' all you have is the two ATA connections. One ATA/33 for the DVD drive and one ATA/66 for the hard drive. I would seriously recommend getting a PCI controller (be it PATA / SATA / SCSI). That way you can achieve this advantage by having separate bus / channels. The ATA/66 interface is certainly fine for one drive (ATA/66 = 66MB/s and most HD's max out at between 35-45MB/s - non-burst...) But for two drives - you're pushing it!
Check out these worthwhile tutorials:
- A Gurus Guide To Macintosh Performance Acceleration
<http://www.macgurus.com/guides/photoshopguide.php>
<http://www.macgurus.com/guides/storageaccelguide.php>
<http://homepage.mac.com/boots911/.Public/PhotoshopAccelerationBasics2.3.pdf>

The G4 L3 cache processor dilemma...

Apple initially started adding L3 cache to it's G4 line when Motorola was having difficulty providing faster processors. It's an old trick - but a successful one. CPU's already have L1 and L2 cache. Generally, most operating systems only need to store a small amount of data that is frequently used by the CPU - and therefore there is a 80-90% possibility that the frequently used data the operating system needs will be in the L1 or L2 cache. If it's not, it will then access RAM. (And if it's not in RAM it will be on the hard drive.) However powerful modern applications (like Photoshop and games) have more than just a little amount of frequently accessed data - they have a sizable chunk, quite often bigger than a few MB's. When these modern programs start up, they load a large amount of data that it 'might' use into RAM. By adding a decent sized L3 cache you can cut out the high latency's (read time) that it takes the CPU to keep accessing this larger amount of frequently used data, because (instead of being in RAM) it is right there in the L3 cache. If there is no L3 cache, the CPU will have to be continually accessing RAM - which is much slower. So depending on the application or the type of processing (music and video files) an L3 cache can provide a significant boost in CPU productivity by either storing frequently used data or by continually keeping the CPU fed with the data it is processing.

But in the G4 machines, the advantage of L3 cache doesn't just stop there. If you go and add a dual processor you soon realise that there is a only a single data path between the processors and the memory controller operating at 133MHz. Both processors are going to have to share that same data path. Without L3 cache, that data path quickly becomes a bottleneck. This was a major design flaw with using dual processors in G4 machines. (And why L3 cache was so highly regarded.) The G5 design rectified the problem by providing each processor with its own data path to memory - and this is why the G5 does not have L3 cache. So you can see that L3 cache can be of great benefit with dual processors in a G4 machine.

Hmmm. > Lets read Apple's marketing hype when the later series G4's were released:

"L3 cache keeps the PowerPC G4’s engine stoked. L3 cache is high-speed Double Data Rate memory. It provides fast access to data and application code through a dedicated bus to the processor. This dedicated bus provides throughput of up to 4 gigabytes per second (GBps), and is completely unhindered by any other data transfers. The high speed made possible by L3 cache, with its dedicated bus, allows the PowerPC G4 processor to receive data more than five times faster than it could from main memory (where a shared bus lowers speed). Because of this low latency, the G4 processor is constantly fed with data. So it doesn’t just sit idle, waiting for the next set of data to arrive. And whether you choose a new Power Mac G4 with a single-processor or dual-processor configuration, you can be sure of one thing: each processor comes with its own dedicated L3 cache. In a dual-processor configuration, this enables both processors to share data seamlessly with each other without pausing to update main memory. The result? Accelerated processing. With up to 2MB of dedicated memory, the L3 cache can store large amounts of active application code and data. When you run an application, most of the active program code and user data remains in the L3 cache. This keeps the most important information instantly accessible to the processor. (It’s analogous to caching web pages on your hard drive: when you click the Back button on your web browser, your computer uses the digital data you downloaded moments before, instead of downloading the same data again.) This is in marked contrast to the situation with PC architecture, where data travels from main memory to the processor through the system controller, elbowing its way through streams of data and instructions from other subsystems. The congestion caused by the merging of these various data streams results in slowdowns in the overall transfer rate and this in turn hampers application performance."
-----------------------------------------------------

So... If L3 cache is so important, why do people even bother with the 7447 processors which has no L3 cache? And why does Apple use the 7447 processor in many of its machines like the 'eMac'?

The answer to this is simple. The 7447 is a newer design that can operate at higher CPU speeds, has much (much) lower power consumption and is cooler operating. It's a bit of a trade off. By providing a slightly larger L2 cache and a faster system bus (the eMac that uses 7447 processors and has a 167MHz system bus) you kind of make up for the lack of L3 cache. (Understand, once you get a G4 processor operating at speeds greater than 1.33GHz the timings with main memory are all out of sync - and an L3 cache becomes a hinderance rather than an asset - as the processor wastes clock cycles (time) searching the L3 cache for what it might need...) Furthermore, it's not just because the 7447 design doesn't support L3 cache - adding fast memory (L3 cache) to a processor is expensive and significantly increases production costs. And then, adding to the confusion is the fact that not all applications need or take advantage of an L3 cache. So, in those situations more MHz is much more desirable. The 'heat' generated by the 7455 can be a problem. You will notice if you look though the forum threads that this issue alone persuaded many to choose the 7447. Heat and power. Because if you want to load your G4 up with other power hungry bits and pieces - you run the risk of overloading the PSU (the Radeon 9800 Pro uses 75W+ alone!).

Gigadesigns somewhere publicly stated that a 1.4GHz 7455 was equal to a 1.73GHz 7447. That gives you an good idea how the two different processors fair up. It was stated that the slower 7455 made up for the 18-19% speed increase because it had an L3 cache. I actually contacted Gigadesigns back in 2005 and this is the response I got;

"Our last build of 7455 upgrades could not be certified across the board at 1.4GHz in the 133MHz machines. I should also note that we are out of stock of all 7455 based upgrades. There is no estimated time when we might build more because of the cost of the 7455 processors and the performance we are getting out of the 7447A. I would like to talk a little more about the benefits etc. of L3 cache (or no L3). In our tests we have seen in a mixed application environment that not having a L3 Cache represents about a 10% penality. That is a Dual 1.8GHz w/o L3 will perform on par with a 1.6GHz with L3. Some applications exaggerate this as they rely more on L3 than others. Others like the OS do not seem to use L3 at all and therefore gain the full performance benefit."

There you have it. A complete analysis of the pro's and con's of L3 cache.
Here is a really good benchmark of the differences:
<http://www.xlr8yourmac.com/G4CARDS/powerlogix_dual_g4_7447_7457/index.html>
And another comparing the different G4's to a G5 - and some really insightful concerns with upgrading a G4.
<http://www.barefeats.com/g4up.html>

Personally, I ended up getting an original Apple dual 1GHz (cheaply off Ebay) and then overclocking it to 1.1GHz. It was a quick fix while a figured out how to rob the local Bank in order to afford a dual 1.8GHz Gigadesigns processor. (And yes - I'm still working on how to rob the Bank...) I personally feel that the (no L3 cache) dual 7447 processor with faster MHz is the way to go... Because although some applications and some types of processing effectively use the L3 cache - the majority don't. ...Then again... for the kind of applications you want to use - you would really appreciate the extra grunt that the L3 cache can provide. I know that Photoshop and Final Cut Pro are both applications that show improvement on a L3 cache enabled processor. The problem is... a top dual processor with L3 cache (dual 1.3GHz+) is out of production and very hard to come across secondhand. So in some ways - you don't really have a choice. As I stated earlier, you would (without a doubt) be better off getting a dual processor over a single one. That's not just because the applications you want to use are dual processor aware - the ability to multitask effortlessly while your Photoshop is busy munching away in the background is heaven. And the added snappy / responsiveness that a dual processor provides with Mac OS X........ nuff said. I stand by my original recommendation - go for the fastest "dual" 7447 (no L3 cache) that you can afford. Judging by the reports that I've encounted - you won't regret it!

Hope all this helps. With all respect - you might just be better off holding out and picking a dual 2GHz G5 on the cheap. Because no matter what you do - the G4 does have architectural and motherboard bus speed limitations that you can never resolve. Then again, if you're like me and have sentimental feelings towards your Quicksilver - it can certainly be upgraded (at a price) to become a very capable imaging workstation...

[PB2K]

I have some news as well :

I toasted my powerlogix 1.33Ghz Dual. First it started crashing, then my USB input devices didn't get power anymore. Ok so I reboot. Then I smelled smoke, but couldn't identify the origin, so I opened up the powermacs case, and smelled smoke coming out of the processor..

****

I replaced it with a 533 mhz processor and thats why i am able to write this post. Djeez this g4 is wasted, it's so slow!!!!!! Well, guess I will have to buy a new computer

[imitchellg5]

That must be incredibly frustrating.

[PB2K]

it was, yeah

[imitchellg5]

Have you contacted Powerlogix at all? Because they really should give you a new one or buy you a new Mac for that.

[PB2K]

i bought both mac and upgrade secondhand

[samuel690069]

Originally Posted by tumbleguts

Hello Samuel,

Caught your thread and thought I'd dispense the wisdom I've acquired having gone thru a similar experience... The Quicksilver is a mighty machine. Sure, it's no G5 - but if you optimize it correctly it can really be something that can handle most graphics / video editing programs with flare... You seemed to have already given it some pretty powerful hardware boosts - such as the Radeon 9800 Pro, some decent hard drives, and 1.5GB of memory. Off the bat - I would recommend two things:
> a dual G4 processor upgrade, and
> optimization of Hard Drives with a dedicated scratch disk.

Let me explain myself. I too have a Quicksilver. It was originally a pedestrian 733MHz - but I've since gone the whole hog and upgraded everything. I'm a graphics professional so I know what works, and what doesn't. For the kind of applications you want to use (and obviously use well) I cannot stress enough the benefit of getting a dual processor over a single. Photoshop, in particular, is one of a few programs that is fully multi-processor aware - and really struts its stuff when running on one. Overall, Mac OS X in general, is a greatly improved beast when running on a dual processor. So... if you decide to go the upgrade route - definitely gone for the dual. Cannot emphasis that enough. Regardless of speed - a dual processor will handle multitasking and processor intensive graphics applications with much more ease. And you'll really appreciate the extra grunt. (But I'll come back to the processor upgrades...)

One thing that most people often overlook when trying to maximize their machines is a correct hard drive setup. You can easily gain a 20-30% performance increase (with applications like Photoshop) by simply providing a dedicated scratch disk on a separate channel. See... the HD is really nearly always the slowest part of any computer. Ideally what you want is 3 separate drives on 3 separate bus / channels. One drive as your startup disk with Mac OS X and all your applications. One (fast) drive as a dedicated scratch disk. And another, (make it large) as your media / backup / storage / file disk. However, it's impossible to do this in a Quicksilver without adding a PCI controller - cos' all you have is the two ATA connections. One ATA/33 for the DVD drive and one ATA/66 for the hard drive. I would seriously recommend getting a PCI controller (be it PATA / SATA / SCSI). That way you can achieve this advantage by having separate bus / channels. The ATA/66 interface is certainly fine for one drive (ATA/66 = 66MB/s and most HD's max out at between 35-45MB/s - non-burst...) But for two drives - you're pushing it!
Check out these worthwhile tutorials:
- A Gurus Guide To Macintosh Performance Acceleration
<http://www.macgurus.com/guides/photoshopguide.php>
<http://www.macgurus.com/guides/storageaccelguide.php>
<http://homepage.mac.com/boots911/.Public/PhotoshopAccelerationBasics2.3.pdf>

The G4 L3 cache processor dilemma...

Apple initially started adding L3 cache to it's G4 line when Motorola was having difficulty providing faster processors. It's an old trick - but a successful one. CPU's already have L1 and L2 cache. Generally, most operating systems only need to store a small amount of data that is frequently used by the CPU - and therefore there is a 80-90% possibility that the frequently used data the operating system needs will be in the L1 or L2 cache. If it's not, it will then access RAM. (And if it's not in RAM it will be on the hard drive.) However powerful modern applications (like Photoshop and games) have more than just a little amount of frequently accessed data - they have a sizable chunk, quite often bigger than a few MB's. When these modern programs start up, they load a large amount of data that it 'might' use into RAM. By adding a decent sized L3 cache you can cut out the high latency's (read time) that it takes the CPU to keep accessing this larger amount of frequently used data, because (instead of being in RAM) it is right there in the L3 cache. If there is no L3 cache, the CPU will have to be continually accessing RAM - which is much slower. So depending on the application or the type of processing (music and video files) an L3 cache can provide a significant boost in CPU productivity by either storing frequently used data or by continually keeping the CPU fed with the data it is processing.

But in the G4 machines, the advantage of L3 cache doesn't just stop there. If you go and add a dual processor you soon realise that there is a only a single data path between the processors and the memory controller operating at 133MHz. Both processors are going to have to share that same data path. Without L3 cache, that data path quickly becomes a bottleneck. This was a major design flaw with using dual processors in G4 machines. (And why L3 cache was so highly regarded.) The G5 design rectified the problem by providing each processor with its own data path to memory - and this is why the G5 does not have L3 cache. So you can see that L3 cache can be of great benefit with dual processors in a G4 machine.

Hmmm. > Lets read Apple's marketing hype when the later series G4's were released:

"L3 cache keeps the PowerPC G4’s engine stoked. L3 cache is high-speed Double Data Rate memory. It provides fast access to data and application code through a dedicated bus to the processor. This dedicated bus provides throughput of up to 4 gigabytes per second (GBps), and is completely unhindered by any other data transfers. The high speed made possible by L3 cache, with its dedicated bus, allows the PowerPC G4 processor to receive data more than five times faster than it could from main memory (where a shared bus lowers speed). Because of this low latency, the G4 processor is constantly fed with data. So it doesn’t just sit idle, waiting for the next set of data to arrive. And whether you choose a new Power Mac G4 with a single-processor or dual-processor configuration, you can be sure of one thing: each processor comes with its own dedicated L3 cache. In a dual-processor configuration, this enables both processors to share data seamlessly with each other without pausing to update main memory. The result? Accelerated processing. With up to 2MB of dedicated memory, the L3 cache can store large amounts of active application code and data. When you run an application, most of the active program code and user data remains in the L3 cache. This keeps the most important information instantly accessible to the processor. (It’s analogous to caching web pages on your hard drive: when you click the Back button on your web browser, your computer uses the digital data you downloaded moments before, instead of downloading the same data again.) This is in marked contrast to the situation with PC architecture, where data travels from main memory to the processor through the system controller, elbowing its way through streams of data and instructions from other subsystems. The congestion caused by the merging of these various data streams results in slowdowns in the overall transfer rate and this in turn hampers application performance."
-----------------------------------------------------

So... If L3 cache is so important, why do people even bother with the 7447 processors which has no L3 cache? And why does Apple use the 7447 processor in many of its machines like the 'eMac'?

The answer to this is simple. The 7447 is a newer design that can operate at higher CPU speeds, has much (much) lower power consumption and is cooler operating. It's a bit of a trade off. By providing a slightly larger L2 cache and a faster system bus (the eMac that uses 7447 processors and has a 167MHz system bus) you kind of make up for the lack of L3 cache. (Understand, once you get a G4 processor operating at speeds greater than 1.33GHz the timings with main memory are all out of sync - and an L3 cache becomes a hinderance rather than an asset - as the processor wastes clock cycles (time) searching the L3 cache for what it might need...) Furthermore, it's not just because the 7447 design doesn't support L3 cache - adding fast memory (L3 cache) to a processor is expensive and significantly increases production costs. And then, adding to the confusion is the fact that not all applications need or take advantage of an L3 cache. So, in those situations more MHz is much more desirable. The 'heat' generated by the 7455 can be a problem. You will notice if you look though the forum threads that this issue alone persuaded many to choose the 7447. Heat and power. Because if you want to load your G4 up with other power hungry bits and pieces - you run the risk of overloading the PSU (the Radeon 9800 Pro uses 75W+ alone!).

Gigadesigns somewhere publicly stated that a 1.4GHz 7455 was equal to a 1.73GHz 7447. That gives you an good idea how the two different processors fair up. It was stated that the slower 7455 made up for the 18-19% speed increase because it had an L3 cache. I actually contacted Gigadesigns back in 2005 and this is the response I got;

"Our last build of 7455 upgrades could not be certified across the board at 1.4GHz in the 133MHz machines. I should also note that we are out of stock of all 7455 based upgrades. There is no estimated time when we might build more because of the cost of the 7455 processors and the performance we are getting out of the 7447A. I would like to talk a little more about the benefits etc. of L3 cache (or no L3). In our tests we have seen in a mixed application environment that not having a L3 Cache represents about a 10% penality. That is a Dual 1.8GHz w/o L3 will perform on par with a 1.6GHz with L3. Some applications exaggerate this as they rely more on L3 than others. Others like the OS do not seem to use L3 at all and therefore gain the full performance benefit."

There you have it. A complete analysis of the pro's and con's of L3 cache.
Here is a really good benchmark of the differences:
<http://www.xlr8yourmac.com/G4CARDS/powerlogix_dual_g4_7447_7457/index.html>
And another comparing the different G4's to a G5 - and some really insightful concerns with upgrading a G4.
<http://www.barefeats.com/g4up.html>

Personally, I ended up getting an original Apple dual 1GHz (cheaply off Ebay) and then overclocking it to 1.1GHz. It was a quick fix while a figured out how to rob the local Bank in order to afford a dual 1.8GHz Gigadesigns processor. (And yes - I'm still working on how to rob the Bank...) I personally feel that the (no L3 cache) dual 7447 processor with faster MHz is the way to go... Because although some applications and some types of processing effectively use the L3 cache - the majority don't. ...Then again... for the kind of applications you want to use - you would really appreciate the extra grunt that the L3 cache can provide. I know that Photoshop and Final Cut Pro are both applications that show improvement on a L3 cache enabled processor. The problem is... a top dual processor with L3 cache (dual 1.3GHz+) is out of production and very hard to come across secondhand. So in some ways - you don't really have a choice. As I stated earlier, you would (without a doubt) be better off getting a dual processor over a single one. That's not just because the applications you want to use are dual processor aware - the ability to multitask effortlessly while your Photoshop is busy munching away in the background is heaven. And the added snappy / responsiveness that a dual processor provides with Mac OS X........ nuff said. I stand by my original recommendation - go for the fastest "dual" 7447 (no L3 cache) that you can afford. Judging by the reports that I've encounted - you won't regret it!

Hope all this helps. With all respect - you might just be better off holding out and picking a dual 2GHz G5 on the cheap. Because no matter what you do - the G4 does have architectural and motherboard bus speed limitations that you can never resolve. Then again, if you're like me and have sentimental feelings towards your Quicksilver - it can certainly be upgraded (at a price) to become a very capable imaging workstation...

Sorry for the v late reply.. very busy travelling overseas recently....Thank you very much for your valueble time & detailed technical info... really appreciated!!!
i think the conclusion will be first : get the 7455 Dual 1.4GHz 2MB L3( if still available..i hav try, but unfortunally their is no more available..OWC, fastmac,amazon,gigadesign,powerlogix,sonnet...etc, if you happen to come across pls let me know,thanks! ) or go for 7447A Dual 1.8GHz 512kb L2 right??
btw, if i go for sonnet 7447A Dual 1.8GHz 512kb L2 together with my Radeon 9800 Pro, will my original Power Supply(AcBel 344watt) handle it ? or need to upgrade to a higher power PSU ?
i dont know any particular supplier / brand / manufacturer on this...
once again thank you very very very much....!!!
warmest regards and all the best,
cheers
samuel