Computer Buying Guide

This is what we all want to do - buy a new computer. The key is to remember that, compared with any 680x0-based Mac, the slowest Power Mac absolutely rocks.

Name Your Need

You've already looked at your old Mac and found it inadequate. There are specific areas (RAM, speed, drive size, networking, video, etc.) that just don't cut it. Since the PPC is so fast, these are the areas you want to address.

Speed

How much is enough? Compared to my old Centris 610, any current Power Mac or clone is mind-bogglingly fast. The slowest desktop I find in the MacMailOrder catalogs is 240 MHz 603e. And the slowest model Apple makes today runs a 233 MHz G3. But CPU speed isn't everything.

First Generation. The 601 came out first and was available in 60-120 MHz speeds.

Second Generation. Next came the 603, a low power version of the 601. This chip was usually put in low end computers with less expensive components (especially hard drives). Because of this, despite being a bit more powerful than the 601, the 603 tended to test slightly slower. For the most part, this has been replaced by the 603e with its larger, more efficient internal cache.

The second generation also includes the 604, with a beefed up math section, a larger cache, and hooks to allow multiple CPUs. Cycle for cycle, the 604 is roughly 50% more efficient than the 601. That is, a 601 would have to run at 150 MHz to match a 100 MHz 604. The 604 topped out at about 150 MHz. A faster version, the 604e, has a larger internal cache than the original 604. It is usually available at speeds of 180 MHz and faster. The 604e is roughly 50% more efficient than the 603e.

Third Generation. IBM and Motorola are shipping third generation PowerPCs. Getting the most press right now is the 750 (aka G3), which benchmarks show to be more efficient than the 604e at the same clock speed. The 750 is optimized to perform best with real software. It also has an on-board cache manager which can be used with inline and backside caches. It seems most 750s will be used with 512 KB to 1 MB backside caches, which contributes greatly to their performance. (There is a less expensive chip, the 740, that doesn't have an on-board cache manager.)

With the 750 outperforming the 604e at the same clock speed - and already available at higher speeds - we might wonder about the future of the 604. The 604 has been redesigned, but not as extensively as the 750. The new 604 uses a smaller die (lower power consumption, less heat generation) and runs at higher clock speeds. Since it still has a stronger math section and supports multiple processors (the 750 doesn't), it may retain its home in high end graphic machines. (For more information on PowerPC chips, click here.)

All that said, just a reminder that every Power Mac and clone is wicked fast compared to our low end computers.

Speed Revisited, the Level 2 Cache

Perhaps the best way to speed up a Power Mac is to give it a larger level 2 cache (level 1 cache is on the chip itself; level 2 may be on the motherboard, inline, or backside). Some Power Macs show nearly a doubling in performance comparing a 1 MB L2 cache with no cache.

Speed Revisited, the System Bus

PowerPC chips and daughtercards keep getting faster, but they are running up against real design issues. At present, even with the new Power Mac G3, the CPU can run no more than seven times faster than the system bus (this is a motherboard limitation; the PowerPC 750 can operate at eight times bus speed). On a Tanzania motherboard and Umax C500/600, the 40 MHz system bus means a top CPU speed of 320 MHz. Tanzania II and Power Macs with daughtercards use a 50 MHz bus, which can reach a top speed of 400 MHz (the 9600/350 reached that speed). Power Computing had models with a 60 MHz system bus, enabling them to reach 480 MHz when chips get that fast.

And the G4 chips, expected in 1999, may offer even higher multiples of bus speed.

Apple's Power Mac G3 uses a 66 MHz bus, allowing for a 466 MHz PPC 750. (For details, see Clocking the Power Mac G3.) The G3 motherboard was designed with the future in mind: although current components may not permit it, there are jumpers to enable 75 MHz and 83 MHz bus speeds. At top speed, the Gossamar design could theoretically support a 583 MHz CPU. Future motherboards may run at 100 MHz, allowing an 800 MHz G3 - or possibly an even faster G4.

Drives

Many of the cheapest Macs and clones don't come with SCSI hard drives and CD-ROM players. To keep costs down, they use EDI hard drives and ATAPI CD-ROMs - just like Wintel clones (Umax did use SCSI CD-ROM in their C500 and C600). This isn't to say they aren't fast, only that they aren't SCSI. Regardless of whether they use SCSI or EDI hard drives, the less expensive computers tend to use less expensive drives, which usually means slower drives.

But when you consider how much computer you're getting for your money (16 MB RAM, 1.2GB hard drive, 8x CD-ROM, 200 MHz or faster CPU), it's downright amazing they can make a profit selling them. The value of entry level Mac OS computers is incredible. And with the iMac selling for under $1,300, there's little reason not to buy a G3 these days. (Okay, not having that much money is a good reason.)

In researching models, be sure to compare hard drive performance - it's something you'll live with daily.

Video

This is one place where cutting corners can cost you performance. The first generation Power Macs (6100, 7100, 8100) used RAM for video. Not VRAM. Not a video card, unless you bought the AV version. The best ways to speed up these computers were adding a video card, a level 2 cache, and Speed Doubler. If that isn't enough, look into chipping the CPU or replacing the motherboard.

The Performa 6400 was a powerhouse in all respects but one: video. Adding a good PCI video card empowered it. Apple learned its lesson and put better video in the Power Mac 6500.

Another interesting example is the Power Mac 7200, which came with 1 MB VRAM. Just adding a second VRAM DIMM provided interleaved video memory and noticeably faster video performance.

In looking at the new computers, be sure to compare the video performance.

Resources

The best places on the internet to find benchmarks for Macs and compatibles are Bare Feats and The Mac and Mac Clone Performance Comparison Page.

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