# PowerPC 7455 vs. 7470

(As well as similar comments here)

"The new 1.25GHz chips are, unfortunately, just upclocked PowerPC 7455 processors, not the PPC 7470s hoped for by the grapevine. This is a dangerous flaw, because the PPC 7455 cannot take advantage of DDR memory -- as on the Xserve, the new PowerMacs will be limited to 1.3GB/s actual processor bandwidth despite 2.7GB/s memory bandwidth on the two high-end models."

The question I have is does each 7455 get its own 1.3GB/s? If this is the case, then 2.6GB/s can be taken up by the 2 processors with 100MB/s left over. I see that each processor has its own L3 so does each have its own pipe to the System Controller?

Is it safe to assume that the new G4s would use "Registered" (4 slots) ECC PC2700 DDR DIMMs?

What interface is the SuperDrive & optional ComboDrive using? (A third ATA, FireWire)

## Comments

288memberThe imaginary 7470 does in fact kick the 7455's ass, but only in Fictionland.

Jet

1,002member166.66 * 64-bits * 2 = 2.666GBps or 2.7GBps rounded.

The fsb has exactally half the throughput of the memory bus. It just appears that the fsb is less than half because Apple rounded their numbers for odvious reasons. Would you rather have them call it a dual 999.99MHz G4?

2member<strong>166.66 (167 rounded) * 64-bits (8-bytes) = 1.333GBps or 1.3GBps rounded.

166.66 * 64-bits * 2 = 2.666GBps or 2.7GBps rounded.

The fsb has exactally half the throughput of the memory bus. It just appears that the fsb is less than half because Apple rounded their numbers for odvious reasons. Would you rather have them call it a dual 999.99MHz G4?</strong><hr></blockquote>

I understand the math but I'm asking if each processor gets its own 1.33GB/s, or do the have to share the same 1.33GB/s. If they use separate pipes, there is no real design flaw...

9,812member1,002member<strong>

I understand the math but I'm asking if each processor gets its own 1.33GB/s, or do the have to share the same 1.33GB/s. If they use separate pipes, there is no real design flaw...</strong><hr></blockquote>

Unfortunately MPX is a shared bus, so each CPUs gets 6.67GBps theoretical. Can you say starvation. Hope the next G4s ditch MPX in favor of something faster. RapidIO? That'll be an excelent stop-gap until the arrival of the PowerMac POWER4 with 6.4GBps independent bus action.

76member<strong>166.66 (167 rounded) * 64-bits (8-bytes) = 1.333GBps or 1.3GBps rounded.

166.66 * 64-bits * 2 = 2.666GBps or 2.7GBps rounded.

The fsb has exactally half the throughput of the memory bus. It just appears that the fsb is less than half because Apple rounded their numbers for odvious reasons. Would you rather have them call it a dual 999.99MHz G4?</strong><hr></blockquote>

I was always under the impressions the numbers are more like 166.666666666666666666... and 133.333333333333333...so it's actually 1GHz since 9.999999.....===10. (this bit of math bothered me for the LONGEST time...since 5th grade when i learned fractions...) But yeah, MPX is horribly out of date now...I wand some Quad pumped bus! (insert Intel crap here)

76member<strong>I understand the math but I'm asking if each processor gets its own 1.33GB/s, or do the have to share the same 1.33GB/s. If they use separate pipes, there is no real design flaw...</strong><hr></blockquote>

No. 2 CPUs get a total of 1.33GB...It'd be way cool if Apple designed a North Bridge that fed each CPU individually. Since they had to redesign the NB anyway, maybe it Does support DDR, just that MPX doesn't, so it can't be utilized...which means that you can put in the MPX+ 7470 chips in the same mobo later and take advantage of the DDR 167 FSB...(I wish)