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A Peek at the Apple Sawtooth (G4/450 AGP System) CPU Module
The Apple G4/AGP systems introduced in Fall 1999 (code named "Sawtooth") have a different motherboard and CPU module design than the previous B&W G3 and PCI based G4 ("Yikes") models. The Sawtooth design includes an AGP graphics card slot, internal Firewire port, dual USB controllers (independent of each other), Airport wireless networking card slot/antenna and a non-ZIF socketed CPU module. (I'm pretty positive there will be Sawtooth CPU upgrades however.)
Many readers had expressed interest in seeing what's under that huge heatsink so I'm posting this to answer those requests. It's humbling to compare the B&W G3 heatsink to the G4 version as the photo below shows. Don't worry - the G4 heatsink may be 4 times as large, but the chip is only about twice as hot according to the chip specs (shown below). Based on what I've seen with G4 CPU upgrades, I think the G3 spec must be low, as I don't think the G4 is actually twice the wattage of the G3.
B&W G3 vs G4 Heatsink
As you can see in the image above - the G4's heatsink is massive, however it never seems to get the least bit warm. I can only guess that Apple provided for the day when there would be two G4s on the module (there appears to be room, if the board had a relayout of components). The existing heatsink would need to be modified for two G4s however, as there is currently a single raised contact 'block' on the back of the heatsink for the CPU.
Future G4s will eventually be lower voltage (dissipating less heat), perhaps enough that by next summer there may be the possibility of a G4 Powerbook. The specs on the current G4/450 shows an 8.9W typical, 16.5W maximum rating (a 400MHz Motorola G3 rates 4.8W/8.0W respectively). Again, I think the Motorola G3 chip may be nearer to 8W typical in my opinion.
After removing the two retaining straps, lifting off the heatsink shows the Sawtooth CPU module.
Sawtooth CPU Module
Note the single cache chip on this side (another one is on the bottom side of the module). With a relayout, I think there is space on this module for two G4 CPUs.
Technical Details/Speed Control Configuration: For a reference only (don't try this at home) page outlining the Bus ratio (Bus/CPU multiplier), Core Voltage, L2 signal level and Bus Clock (PCI/AGP) timing info, see Michiro Isobe's Sawtooth CPU module details article published here.
PowerPC 7400/G4 Specs: Based on Motorola info as of late August. 500MHz and faster versions due (in mass) early next year. My sources indicate it may have a 10x or 12X bus/CPU ratio. All specs subject to change of course.
based on 8/99 specs
CPU speed - Internal
x3, x3.5, x4, x4.5, x5, x5.5,
x6, x6.5, x7, x7.5, x8, x9
(my sources mentioned 10x or 12X in next rev)
Bus Protocol MPX/60x Instructions per Clock
L1 Cache Size
32 Kbyte inst
32 Kbyte data
Backside L2 Cache
512 Kbyte, 1 Mbyte,
or 2 Mbyte
Backside Cache Ratios
(CPU speed/cache speed ratio)
1:1,1.5:1, 2:1, 2.5:1,
3:1, 3.5:1, 4:1
400 MHz: 7.9W/15.5W
450 MHz: 8.9W/16.3W
83 sq mm
0.15 micron 6LM CMOS
1.8 / 2.15V internal,
1.8 / 2.5 / 3.3V I/O
21.4 @ 450 MHz
SPECfp95 (est.) 20.4 @ 450 MHz Other Performance 825 MIPS @ 450 MHz Execution Units
- Sawtooth CPU module details (technical info on speed controls, core voltage and more)
- Comparing the G4 to the G3 (specifications/features)
- Apple Developer Notes on the G4 systems
- G4 Upgrades in B&W G3 vs Sawtooth G4/450 AGP performance (included in my XLR8 G4/400Z Review and Newer Tech G4/400 ZIF Review)
- For more info on the PowerPC 7400 (G4) CPU, see Motorola's PowerPC 7400 (G4 CPU) page (Includes a JPEG image of the die) and their PDF file on the G4. Also check this August 27th, 1999 updated 7400/G4 Specs PDF File.
- First Look at the XLR8 G4/400 CPU upgrade (includes G3/400 vs G4/400 tests in an 9500/Genesis Mac).
- G4 Forums - discuss G4 system and upgrade topics in this message board.
- My recent MAChCarrier G3/500 review has some (non-altivec) application comparisons with the G4/450 sawtooth system.
- Graphics Cards Tests in a G4/450 (including Voodoo3 3000 AGP, Rage128 AGP, and Voodoo3 3000 PCI). See how other G4 owners rated graphics card performance in my Mac Game Framerates searchable database.
- Other Articles and Site content.
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