[reemas]

Can someone please help:
I posted before asking the diff between notebooks and desktops with the same specifications. For the most part I now know that unless the specs are truly identical, desktops are faster.

But someone said usually 1 GHz notebook doesn't have the same cache and bus speeds as a 1GHz desktop.

I looked this up on Apple's site and noticed the following:

Current model powerbooks (15-inch):
1GHz or 1.25GHz PowerPC G4 processor with Velocity Engine
512K SRAM on-chip L2 cache
167MHz system bus

Previous generation G4 PowerMacs:
1.25GHz PowerPC G4 processor
Full 128-bit internal memory data paths
256K on-chip L2 cache running at processor speed
1MB DDR SRAM L3 cache per processor (2MB DDR SRAM L3 cache per processor with dual 1.25GHz PowerPC G4 build-to-order option)
167MHz system bus supporting over 1.3GBps data throughput

Could someone please explain L2 vs L3 cache and what it means and does to me?
Also, where does bus speed come in and how does it affect things?
I'm guessing the desktop is faster?

Thanks for your time.

[KraziKid]

Originally posted by reemas:
Can someone please help:
I posted before asking the diff between notebooks and desktops with the same specifications. For the most part I now know that unless the specs are truly identical, desktops are faster.

But someone said usually 1 GHz notebook doesn't have the same cache and bus speeds as a 1GHz desktop.

I looked this up on Apple's site and noticed the following:

Current model powerbooks (15-inch):
1GHz or 1.25GHz PowerPC G4 processor with Velocity Engine
512K SRAM on-chip L2 cache
167MHz system bus

Previous generation G4 PowerMacs:
1.25GHz PowerPC G4 processor
Full 128-bit internal memory data paths
256K on-chip L2 cache running at processor speed
1MB DDR SRAM L3 cache per processor (2MB DDR SRAM L3 cache per processor with dual 1.25GHz PowerPC G4 build-to-order option)
167MHz system bus supporting over 1.3GBps data throughput

Could someone please explain L2 vs L3 cache and what it means and does to me?
Also, where does bus speed come in and how does it affect things?
I'm guessing the desktop is faster?

Thanks for your time.

L2 cache is cahce that is located on the CPU die. To retrieve information from it, very little time is lost. L3 cache is cache located off of the die. This saves money to produce like this, but suffers because to access the L3 cache, you must go through the system bus. The bus speed is the speed at which the processor connects to the rest of the system (RA for instance). The faster the bus speed, the faster data can be moved from the RAM to the processor. The current generation PowerBooks offer similar to better performance vs. that other PowerPC processor. Certain programs however benefit from L3 cache (they are programmed to utilize it). It's a crap shoot. In general, more L2 cache will offer greater performance because more instructions can be held on the chip.

[Commodus]

I would actually go so far as to say that the PowerBook can be as fast or faster in some circumstances, though not always.

Like KraziKid said, the L3 cache can sometimes be helpful. However, that mainly applies to apps that overflow the L2 cache and/or are told to look for L3. Having double the L2 cache means that instructions that don't exceed the L2 cache's capacity - of which there are many - will take less time to be processed.

The only other things that slow the PowerBook down are laptop-specific. A 4200 or 5400 RPM drive isn't going to be as fast as a 7200 RPM desktop drive. Likewise, a Mobility Radeon 9600 isn't going to be as fast a graphics chip as a desktop's Radeon 9600 Pro. But if you have lots of RAM and aren't dependent on good 3D performance, the PowerMac's advantages may not matter.