re4mat
Well-known member
Back in the early 2005, Daystar was selling a PowerPC 7457 upgrade for the iMac G4 (PowerMac4,2), which replaced its original PowerPC 7450. Obviously they no longer offer this, but it does prove that you can put a 7457 in an original iMac G4 to bump it up to 1.35GHz. So, in short, I want to do this to my iMac.
I've been doing some research on the 7457, and one thing I've found was that there were several varieties of the 7457 made. For example, even though many sources claim that Apple never used the 7457 in their machines, the original iBook G4s did. But those were a low-power version, running around 800MHz on a 133MHz bus with a core power supply of 1.1V. (The original iMac G4, for comparison, ran on a 100MHz bus at 1.3V.) Which one? I have no clue, since I don't have an iBook G4 to crack open and look at.
NXP, who used to sell them (and possibly might still?), has a listing of 9 different varieties. Unfortunately, I don't know which one Daystar used in their upgrade. I have found someone on eBay who's selling 4 of the MC7457RX1267LC chips, though, which has the right package type (CBGA483 - ceramic, ball grid array, 483 balls; 1.27 mm pitch; 29 mm x 29 mm x 3.2 mm body) to be pin-compatible with the 7450, and can run with a core power supply of 1.3V. So in theory it should be a drop-in replacement. And, in fact, the documentation I have on the 7457 mentions that "the MPC7457 is a footprint-compatible, drop-in replacement in a MPC7455 application if the core power supply is 1.3 V." (Looking in the documentation for the 7455, it mentions that "the MPC7455 is footprint-compatible with the MPC7450 and MPC7451".)
According to the documentation on the 7457, the 1267 in the part number means it's a 1267MHz chip. Page 50, Table 18 shows the PLL configurations for various bus-to-core multipliers to get different core frequencies. It does say to "[n]ote that these configurations were different in some earlier MPC7450-family devices and care should be taken when upgrading to the MPC7457 to verify the correct PLL settings for an application." I found a page that has several resistor configurations to change the bus multiplier on the original iMac G4's logic board. Since it's a 100MHz bus, it's easy to extrapolate the bus multipliers in the chart as 7x, 7.5x, 8x, 9x, and 10x. (Although he's got the configuration for 7.5x wrong, as I'll explain in the next paragraph.) 13.5x isn't on that chart, but we can infer that there is a configuration that sets it to a 13.5x multiplier, since that's presumably what Daystar used to get a clock frequency of 1350MHz in their upgrade. It then becomes a matter of finding what that configuration is—and I think it's moving the resistors to R252, R248, R249, R265, and R266.
In the documentation for the 7450, Table 16 on Page 36 shows the PLL configurations for the 7450 using a 600MHz chip as the example. The PLL_EXT value is given as a bit—either a 0 or a 1—and the PLL_CFG[0:3] value is given as a string of 4 bits. If you concatenate PLL_EXT and PLL_CFG[0:3], the bits for 7x, 8x, 9x, and 10x match what's in ThunderNerd's chart if you see the top row as 1 and the bottom row as 0. For example, with 8x, the concatenated PLL configuration is 01100; switching over to ThunderNerd's chart, he's got 800Mhz listed as bottom top top bottom bottom. The same pattern holds true for all the other whole number multipliers on his chart—they all match up with the 7450 documentation if you assume the top row is 1 and the bottom row is 0. This is why I think he got the configuration for 7.5x wrong; he's got no resistors on any of the pads, but the concatenated PLL configuration for 7.5x in the 7450 documentation is 00001.
So remember that note I mentioned two paragraphs ago that said the configurations were different in earlier 7450 devices? Well, if you look at Table 18 on the 7457 documentation, sure enough the configurations are different. If we assume, however, that the same pattern of top=1 and bottom=0 holds true, then the 13.5x PLL_CFG[0:4] value of 11100 should correspond with having resistors on R252, R248, R249, R265, and R266.
According to the PLL configurations of the 1267MHz chip in Table 18, however, a 13.5x multiplier on a 100MHz bus (to get the 1.35GHz of Daystar's upgrade) results in "core and/or VCO frequencies that do not comply with the 1-GHz column in Table 8." The part I'm confused about, though, is that there is no "1-GHz column" in Table 8. Unless they mean the 1000Mhz column? But that is for a 1000MHz chip, not a 1267MHz chip. I'm not quite sure what to make of that "warning". If anyone has any ideas, I'm all ears. But even doing, say, a 12.5x multiplier to get 12.5GHz wouldn't be that bad. That's still a 56% increase in core frequency over the original chip, which wouldn't be anything to look down on.
So I think I'm going to pull the trigger and buy one of those MC7457RX1267LC chips on eBay. It's $360, but I don't really mind; I love my iMac G4, and to see it get such a huge upgrade would warm my heart. I'll have to wait until I get home in September to put it in, but that just means more time for research. If anyone has any helpful input, I'd love to hear it.
One note: Everymac.com says that the original iMac G4 has a 7445 processor; but if that were the case, then Daystar wouldn't have been able to install a 7457 in them, since they're not pin-compatible. Mactracker.app lists it as having the 7450, which makes a lot more sense.
I've been doing some research on the 7457, and one thing I've found was that there were several varieties of the 7457 made. For example, even though many sources claim that Apple never used the 7457 in their machines, the original iBook G4s did. But those were a low-power version, running around 800MHz on a 133MHz bus with a core power supply of 1.1V. (The original iMac G4, for comparison, ran on a 100MHz bus at 1.3V.) Which one? I have no clue, since I don't have an iBook G4 to crack open and look at.
NXP, who used to sell them (and possibly might still?), has a listing of 9 different varieties. Unfortunately, I don't know which one Daystar used in their upgrade. I have found someone on eBay who's selling 4 of the MC7457RX1267LC chips, though, which has the right package type (CBGA483 - ceramic, ball grid array, 483 balls; 1.27 mm pitch; 29 mm x 29 mm x 3.2 mm body) to be pin-compatible with the 7450, and can run with a core power supply of 1.3V. So in theory it should be a drop-in replacement. And, in fact, the documentation I have on the 7457 mentions that "the MPC7457 is a footprint-compatible, drop-in replacement in a MPC7455 application if the core power supply is 1.3 V." (Looking in the documentation for the 7455, it mentions that "the MPC7455 is footprint-compatible with the MPC7450 and MPC7451".)
According to the documentation on the 7457, the 1267 in the part number means it's a 1267MHz chip. Page 50, Table 18 shows the PLL configurations for various bus-to-core multipliers to get different core frequencies. It does say to "[n]ote that these configurations were different in some earlier MPC7450-family devices and care should be taken when upgrading to the MPC7457 to verify the correct PLL settings for an application." I found a page that has several resistor configurations to change the bus multiplier on the original iMac G4's logic board. Since it's a 100MHz bus, it's easy to extrapolate the bus multipliers in the chart as 7x, 7.5x, 8x, 9x, and 10x. (Although he's got the configuration for 7.5x wrong, as I'll explain in the next paragraph.) 13.5x isn't on that chart, but we can infer that there is a configuration that sets it to a 13.5x multiplier, since that's presumably what Daystar used to get a clock frequency of 1350MHz in their upgrade. It then becomes a matter of finding what that configuration is—and I think it's moving the resistors to R252, R248, R249, R265, and R266.
In the documentation for the 7450, Table 16 on Page 36 shows the PLL configurations for the 7450 using a 600MHz chip as the example. The PLL_EXT value is given as a bit—either a 0 or a 1—and the PLL_CFG[0:3] value is given as a string of 4 bits. If you concatenate PLL_EXT and PLL_CFG[0:3], the bits for 7x, 8x, 9x, and 10x match what's in ThunderNerd's chart if you see the top row as 1 and the bottom row as 0. For example, with 8x, the concatenated PLL configuration is 01100; switching over to ThunderNerd's chart, he's got 800Mhz listed as bottom top top bottom bottom. The same pattern holds true for all the other whole number multipliers on his chart—they all match up with the 7450 documentation if you assume the top row is 1 and the bottom row is 0. This is why I think he got the configuration for 7.5x wrong; he's got no resistors on any of the pads, but the concatenated PLL configuration for 7.5x in the 7450 documentation is 00001.
So remember that note I mentioned two paragraphs ago that said the configurations were different in earlier 7450 devices? Well, if you look at Table 18 on the 7457 documentation, sure enough the configurations are different. If we assume, however, that the same pattern of top=1 and bottom=0 holds true, then the 13.5x PLL_CFG[0:4] value of 11100 should correspond with having resistors on R252, R248, R249, R265, and R266.
According to the PLL configurations of the 1267MHz chip in Table 18, however, a 13.5x multiplier on a 100MHz bus (to get the 1.35GHz of Daystar's upgrade) results in "core and/or VCO frequencies that do not comply with the 1-GHz column in Table 8." The part I'm confused about, though, is that there is no "1-GHz column" in Table 8. Unless they mean the 1000Mhz column? But that is for a 1000MHz chip, not a 1267MHz chip. I'm not quite sure what to make of that "warning". If anyone has any ideas, I'm all ears. But even doing, say, a 12.5x multiplier to get 12.5GHz wouldn't be that bad. That's still a 56% increase in core frequency over the original chip, which wouldn't be anything to look down on.
So I think I'm going to pull the trigger and buy one of those MC7457RX1267LC chips on eBay. It's $360, but I don't really mind; I love my iMac G4, and to see it get such a huge upgrade would warm my heart. I'll have to wait until I get home in September to put it in, but that just means more time for research. If anyone has any helpful input, I'd love to hear it.
One note: Everymac.com says that the original iMac G4 has a 7445 processor; but if that were the case, then Daystar wouldn't have been able to install a 7457 in them, since they're not pin-compatible. Mactracker.app lists it as having the 7450, which makes a lot more sense.
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