Should Apple Use the New G3?
There's been some interesting discussion of IBM's new PowerPC 750CX and forthcoming 750CXe processors, especially related to IBM discusses new PowerPC chips on MacWeek. A lot of Mac users seem to think the 750CX would be a poor choice; I beg to differ.
The biggest difference between the 750CX and the old 750 (commonly known as the G3 in Macintosh circles) is the integrated 256 KB level 2 (L2) cache.
External L2 Cache
The old 750 supports an external L2 cache in sizes of 256, 512, and 1024 KB. Apple has only produced one model, the "Road Apple" PowerBook G3 Series I at 233 MHz, which has used the G3 without a cache - and performance suffered significantly in comparison to the later PB G3 Series II 233 MHz model which did include a cache.
IBM has provided some comparisons for the G3 with various cache sizes. The numbers are rounded off, but a G3/400 with a 256 KB 200 MHz L2 cache* and a 100 MHz system bus (the configuration of the Yosemite G3/400) scores approximately 15 using the SPECint95 benchmark. Doubling the L2 cache to 512 KB increases that to roughly 17, and going to a 1 MB L2 cache brings the SPECint95 score to about 18.
With the old G3, the PowerBook G3 demonstrated that a 512 KB L2 cache improved performance by about 40%. Thus, a G3/400 with no L2 cache would be expected to score about 12 on the SPECint95 benchmark. Adding a 1 MB L2 cache improves that by about 50% - very impressive.
Internal L2 Cache
The new G3 (750CX) doesn't use an external L2 cache. The internal cache is 256 KB in size and runs at full CPU speed, giving it a distinct advantage over the external 256 KB L2 cache. In fact, IBM has benchmarked the 400 MHz 750CX at 16 using SPECint95. That's one-third faster than a cacheless G3, about 6.5% faster than the old G3 with a 256 KB cache, and about 6% slower than the current G3 with a 512 KB cache.
Of course, the G3/400 came with a 1 MB L2 cache, so the 750CX won't quite match it's performance. In fact, it will be about 12% slower - but a 450 MHz 750CX will match the performance of a G3/400 with a 1 MB external cache.
All of this closely matches IBM's theoretical analysis, which points to the 750CX being 6.5% faster than a G3 with a 256 KB cache. The same theoretical model points to a 512 KB internal L2 cache offering an insignificant (1.5%) improvement over a 256 KB cache.
The Benefits of 750CX
I believe Apple should adopt the new IBM processor for the iBook, iMac, and PowerBook. It may not match the performance of a G3 with a larger external cache, but it has the following benefits:
- The 750CX uses less power than the 750, about 4W at 400 MHz vs. 7W.
- An external L2 cache draws power, reducing battery life in a portable. The 750CX doesn't use an external cache.
- Putting a G3 along with L2 cache chips and other support circuitry is an expensive process. With the 750CX, there's just one chip to plug in, reducing complexity.
- It's also less expensive to buy the 750CX than a G3 plus cache chips plus the board they sit on.
- Today's computers are plenty fast. Being 5-15% slower than some theoretical maximum is virtually unnoticeable.
Based on IBM's data, a iBook with a 750CX at 400 MHz would be about 25% faster than the current 300 MHz model and roughly equal to the iBook SE in performance while using a less expensive processor that draws less power. Likewise, a PowerBook with a 750CX at 550 MHz would offer comparable power to the PowerBook 500 while reducing power consumption.
In the end, Apple would benefit from moving to the 750CX for their consumer line. It will reduce costs, making these machines even more affordable, increase battery life, and give Apple a boost in the megahertz wars.
That's something work discussing, especially in the engineering and marketing departments.
Update: On Sept. 13, 2000, Apple announced the second-generation iBook and iBook SE, both running the 750CX processor. Apple managed to trim US$100 from the iBook's price while boosting CPU speed and adding FireWire. The iBook SE received a DVD-ROM drive and faster processor with no change in price.
* Note that some less expensive Macs run the cache at only 40% of CPU speed. This provides lower performance than a cache running at 50% of CPU speed.
- Hands on the FireWire iBook, the first Mac with the 750CX
- The Truth About the New G3
- 466 MHz FireWire iBook vs. 400 MHz Pismo PowerBook, Bare Feats, 10/23/00. Real world tests with iMovie, Cinema 4D, and Bryce.
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.
Recent articles by Dan Knight
- The Late 2012 iMac Value Equation, 2012.10.31. Thinner, lighter, faster, USB 3, improved graphics, Fusion Drive option, and no SuperDrive sum up the new iMacs.
- The 13" Retina MacBook Pro Value Equation, 2012.10.30. Take the 13" MacBook Pro, add a Retina Display, remove the SuperDrive, and drop almost a pound from its weight.
- The Late 2012 Mac mini Value Equation, 2012.10.29. The entry-level Mac mini is a nice step up, but the top-end quad-core model is a powerhouse.
- More in the Mac Musings index.
Links for the Day
- Mac of the Day: PowerBook 145, introduced 1992.08.03. About 70% faster than the 140, the 25 MHz 145 was quite a value.
- May 21 in LEM history: 99: Not censorship - 01: USB and FireWire drives - 02: Hooked by a PowerBook - Printer sharing for Mac OS X - 04: Less frequent OS X uprades: Good or bad? - 07: I won't get an iPhone this year - Can 262,144 colors be considered 'millions'? - Most durable 'Book - 3 GB in a Mac mini? - 08: Quadra a great server for vintage Mac network
- Support Low End Mac
Recent Content on Low End Mac
- World Book Encyclopedia 2012 DVD, Tommy Thomas, Reviews, 2013.03.05. "You may be asking yourself, in an age of Wikipedia and instant information, is World Book still relevant?"
- Vintage Computer Festival SouthEast, April 20-21, 2013, Simon Royal, Mac Spectrum, 2013.02.25. Old Apple gear and old PCs.
- iMessage: The Ultimate Messaging Service?, Simon Royal, Mac Spectrum, 2013.02.21. In most ways, Apple's iMessage is far superior to BlackBerry Messenger.
- More links in our archive.
- Best Mac mini Deals
- Best 13" MacBook Pro Deals
- Best Intel iMac Deals
- Best iPod touch Deals
- Best iPhone Deals
- Best iPod nano Deals
- Best iPod classic Deals
- Best Apple TV Prices
- More deals in our archive.
Low End Mac Reader Specials
Cult of Mac
Shrine of Apple
The Mac Observer
Accelerate Your Mac
The Vintage Mac Museum
Mac Driver Museum
System 6 Heaven
System 7 Today
the pickle's Low-End Mac FAQ