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Mac Musings

The Celeron Effect

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- 8 June 2000 - Tip Jar

Once upon a time Intel created a cheap version of the Pentium and named it Celeron. It had no level 2 (L2) cache, and it sucked. Thus was born the Celeron A, the same basic CPU, but this time with a 128K on-chip L2 cache. The cache runs at full CPU speed, making the Celeron more efficient than the Pentium III (with a 512k half-speed cache) at the same clock speed.

Intel doesn't advertise that fact. They want to sell more of the expensive processors, but Wintel and Linux geeks looking for the most bang for the buck are buying Celerons. If we ever buy a PC for home (our home schooling software requires Windows, although we find Virtual PC satisfactory at present), it's the way I'd go.

The New G3s

PowerPC 750CXIBM announced the PowerPC 750CX and 750CXe this week, the next generation of the PowerPC 750 that Mac users know as the G3 processor. I don't know if they plan on calling it the G3+, but I think they should.

Advantages of the 750CX and CXe include:

  • IBM copper and SOI technology allows 0.18 micron design
  • lower power consumption, 4W at 400 MHz
  • faster processor speeds: 350-550 MHz for the CX, 500-700 MHz for the CXe
  • runs at up to 10x motherboard speed
  • less expensive to implement

The 750CXe has the potential to run at 666 MHz on beige G3s, 1 GHz on blue ones. As far as upgrades for earlier Macs and clones, the 10x multiplier could result in speeds ranging from 333 MHz to 600 MHz. This can help close the perceived MHz gap between today's 500 MHz Macs and a handful of expensive 1 GHz Windows boxes, although it's only a single step toward closing the gap. On the other hand, if IBM moves to 0.15 micron technology, as used by Motorola in the G4, we can expect even higher chip speeds.

The on-chip L2 cache has two significant advantages over the external caching used with the G3 and G4. First, it's fast. As Intel users have discovered, a small but fast cache can outperform a large but slow one. We're about to experience the same thing.

The other advantage is that the faster cache eliminates the need for an external L2 cache. With a price of $77 (10,000 units at 350 MHz) and no need to buy and install a cache, the next generation iBook, iMac, and PowerBook should offer a good deal more performance with no increase in price.

In terms of overall performance, there are no Mac-based benchmarks yet. However, both IBM and Motorola have CPU specifications on their sites, making it possible to compare the G4/450 to the 750CX/450 on industry standard tests. The G4 scores approximately 21.4 on the SPECint95 benchmark, while the 750CX has a base performance of 18.0 (19.2 peak). The G4 is almost 20% faster at integer math.

The other popular test is SPECfp95, which measures floating point performance. Here the G4/450 scores roughly 20.4, while the 750CS has a base of 12.5 and a peak of 12.8. In this instance, the G4, which has two floating point units, is about 60% faster than the G3.

The other commonly used rating is MIPS, or million instructions per second. Motorola rates the G4/450 at 825 MIPS, while IBM claims 1,044 MIPS for the 750CX/450. Advantage G3+ by about 25%. (For comparison, the original Macintosh of 1984 ran at 0.7 MIPS - today's Macs are up to 1,500 times faster! The "wicked fast" Mac IIfx of 1990 scored 10.0 MIPS; today's iBook is about 50 times more powerful.)

Of course, these are theoretical benchmarks. What we really want to know is how well does it perform in Photoshop, how quickly can it crunch a work unit for SETI@home, and how will the new chips compare in the real world to the old G3 and current G4.

Time will tell. My biggest question is who will be first to ship a 750CX: Apple, Newer Technology, XLR8, Sonnet Technology, Powerlogix, or someone else.

In the end, I think we'll all be very happy with IBM's latest version of the G3. But if the 700 MHz version is available immediately, Intel won't be.

I've received a number of emails informing me that the Coppermine Pentium III uses a full-speed 256k on-chip L2 cache. This doesn't change the fact that the Celeron A held its own against the earlier Pentium III. If anything, it validates the importance of a fast cache, which I see as the key improvement in the PowerPC 750CX and CXe. dk

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Dan Knight has been using Macs since 1986, sold Macs for several years, supported them for many more years, and has been publishing Low End Mac since April 1997. If you find Dan's articles helpful, please consider making a donation to his tip jar.

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