All Macs In-Depth Tests

PowerPC vs PowerPC : A Comparison Of The G3 and G4 Processors

Below you will find a features comparison between the current G3 processor and the G4 which is now being used in the current PowerMac G4 computers form Apple. We have also included some benchmarks comparing the two chips. The benchmark used to test the chip's performance does not utilize the "Velocity Engine"(AltiVec) of the G4. So the chip's integer performances are basically the same at similar clock speeds. At the moment there is not much software out there that takes advantage of the "Velocity Engine." Hopefully in the coming year this will change dramatically and we will see the G4 cleaning the G3's clock. Benchmarking programs such as SPEC95 and MacBench will have to be updated to reflect the true potential of the G4 chip. It is still interesting to note the G4's significantly improved floating point performance which should be welcomed in the scientific and graphics fields.

PowerPC Chip Features Comparison
Specs PowerPC G3 (750) PowerPC G4 (7400)
CPU Bus Dividers 3X, 3.5X, 4X, 4.5X, 5X, 5.5X, 6X,6.5X, 7X, 7.5X, 8X, and 10x x3, x3.5, x4, x4.5, x5, x5.5, x6, x6.5, x7, x7.5, x8, x9
Bus Interface 64-bit data
32-bit address
Instructions Per Clock 3 (2+branch) 3 (2+branch)
L1 Cache 32K Instruction
32K Data

32K Instruction
32K Data

Backside L2 Cache Support Supports 256 KB, 512 KB or 1 MB 512K, 1MB or 2MB
Core-to-L2 Frequency Divisions 1:1, 1.5:1, 2:1 2.5:1, 3:1 1:1,1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1
Typical/Max Power Dissipation 4.7W @ 400 MHz 5.0W/11.5W @ 400 MHz
Die Size 40 sq mm 83 sq mm
Transistors 6.35 million 6.5 million

Processor Performance Comparisons -SPEC 95

Below you will find processor comparisons for PowerPC G4 and G3 chips that are based on the manufacturer's published results.

The results directly below were obtained by using the benchmarking program SPECint 95 which measure Integer intensive tasks


The results below were obtained by using the benchmarking program SPECfp 95 which measures Floating Point intensive tasks

Previous Processor comparisons. Your feedback on these results

Actual Scores

Processor SPECint95 SPECfp95
PowerPC G4 21.4 20.4
PowerPC G3 21.4 13.8

What Is SPEC?

SPEC, the Standard Performance Evaluation Corporation, is a non-profit corporation formed to "establish, maintain and endorse a standardized set of relevant benchmarks that can be applied to the newest generation of high-performance computers" (quoted from SPEC's bylaws). The founders of this organization believe that the user community will benefit greatly from an objective series of applications-oriented tests, which can serve as common reference points and be considered during the evaluation process. While no one benchmark can fully characterize overall system performance, the results of a variety of realistic benchmarks can give valuable insight into expected real performance.

SPEC is a non-profit corporation registered in California.

SPEC basically performs two functions:

SPEC develops suites of benchmarks intended to measure computer performance. These suites are packaged with source code and tools and are extensively tested for portability before release. They are available to the public for a fee covering development and administrative costs. By license agreement, SPEC members and customers agree to run and report results as specified in each benchmark suite's documentation. SPEC publishes news and benchmark results in The SPEC Newsletter and The GPC Quarterly. Both are available electronically through (and available in paper as a quarterly publication if necessary) this provides a centralized source of information for SPEC benchmark results.

SPEC95 refers to the total SPEC95 product provided by SPEC. SPEC95 is composed of two suites of benchmarks:

SPEC CINT95: a set of eight compute-intensive integer/non-floating point benchmarks SPEC CFP95: a set of 10 compute-intensive floating point benchmarks

These are intended to provide a measure of compute-intensive performance of the processor, memory hierarchy and compiler components (the 'C' in CINT95 and CFP95) of a computer system for comparison purposes.

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Internal Links

External Links

  • Motorola - detailed information about the various PowerPC chips
  • PowerPC - source data for the benchmarks above
  • SPEC 95 FAQ - all your questions about SPEC 95 answered