The 9500 sports a top-of-the-line PowerPC 604 CPU and PCI bus, too
Tom Thompson
With the latest PowerPC 604 processor and a retooled I/O system, Apple's new
Power Mac 9500
delivers great performance. Using the industry-standard PCI expansion bus, the latest Power Macs should spawn a wide selection of fast, lower cost Mac/PCI peripherals. Most important, the 9500 maintains software compatibility despite big I/O system changes.
The Power Mac 9500 comes in 120-MHz and 132-MHz versions: the 9500/120 and the 9500/132, respectively. Base RAM starts at 16 MB (expandable to 768 MB) with a 512-KB secondary RAM cache. Standard features include six PCI-bus slots, a 1- or 2-GB Fast SCSI drive, a quad-speed CD-ROM drive, two GeoPort serial ports, and two Ethernet ports (10Base-T and AUI). An internal bus s
upports SCSI-2 fast transfers, while the external SCSI bus (standard Macintosh DB-25) handles slower external devices.
Next-Generation Design
Apple created a second-generation architecture for the 604. First, there's that industry-standard, 33-MHz PCI expansion bus (see "Inside the PCI Local Bus," February 1994 BYTE). Most internal I/O subsystems use Open Firmware and the PCI bus for start-up configuration and data transactions. Currently, Open Firmware isn't required for PCI card firmware to operate on the 9500 except with boot devices (such as display or network cards). The system also uses Open Transport, a Unix network standard, to implement its network interface and protocol stacks.
The 9500's memory subsystem is 16 to 20 percent faster than those of previous designs. Memory interleaving generates 128-bit-wide memory accesses. The memory controller is smarter about accesses as well; it monitors memory paging to reduce virtual memory overhead and uses DMA for block tra
nsfers. It also snoops memory accesses and can thus cache such previously uncachable transfers as I/O and video frame buffers. Finally, copy-back caching algorithms reduce bus traffic.
The memory bus speed is programmable (up to 50 MHz), which enables better synchronization of RAM accesses with the processor bus and allows CPU upgrades (up to a 150-MHz 604), because the 604 sits on a plug-in daughtercard.
It's important to note that the 9500 uses 168-pin JEDEC dual in-line memory modules (DIMMs) instead of the 72-pin SIMMs found in existing Power Macs. If you step up to a Power Mac from an older system with lots of memory, you have two options: You can pony up lots of cash for new DIMM memory, or you can use Newer Technology's DIMM Tree ($69; (800) 678-3726), a slick little gizmo that plugs into the 9500's DIMM sockets and provides SIMM sockets for your old RAM (provided it's 70-nanosecond or faster).
Hard disk I/O has been a Power Mac bottleneck, but the 9500 fixes that with native code for
the SCSI driver instead of 680x0 code. (However, file system software is still 680x0 code that undergoes emulation.) Last, the SCSI and other I/O subsystems use a descriptor-based DMA control that minimizes CPU involvement (see the sidebar "Smarter DMA").
The 9500 ships with a tuned up OS, System 7.5.2. Its faster 680x0 emulator uses dynamic recompilation (see "Building the Better Virtual CPU," August BYTE). Other OS optimizations include more native code (such as in the SCSI Manager), some device drivers, and network protocol stacks. Existing native portions of the OS, such as QuickDraw, the math library, and Memory Manager, are tuned for the 603 and 604.
Trial Run
We tested a Power Mac 9500/132 with 32 MB of RAM, a 2-GB hard drive, and ATI's Mac-adapted PCI display card. The ATI card uses QuickDraw's new acceleration API, which makes for snappy screen drawing. With the 604, the Power Mac pulls substantially ahead of similar-speed Pentium systems in both integer and floa
ting-point performance, thanks to a faster CPU and compiler improvements (see the figure
"PowerPC Surpasses Speediest Pentium"
). An improved compiler enhances a system's performance in our native-mode benchmarks, just as it will enhance application speed.
Low-level 680x0 tests show that the 9500 memory subsystem is several times faster than that of a 110-MHz 601-based Power Mac. On application tests, disk I/O was also noticeably faster. Considering the complete overhaul of the Power Mac bus and network interface, there are surprisingly few incompatibilities. The usual assortment of applications, Control Panels, and Extensions -- both native and 680x0 -- functioned as they should. Lotus's cc:Mail worked over the network connection with just one nonreproducible glitch.
We experienced troubles with downloads using Aladdin's SITcomm terminal program. When a noisy connection caused this normally reliable program to abort a ZMODEM transfer, it failed to recover. We also discovered
that an old SCSI tape drive would hang the system unless we switched on the drive after the 9500 booted.
It's now too soon to tell how well the first Mac-compatible PCI cards will work. Companies such as Rockwell (FDDI network card) and Diamond Multimedia (accelerated display card) should have products shipping by the time you read this.
Despite some teething pains, the 9500 provides plenty of horsepower for those who need it. You can expect vendors to correct problems and revise applications to make best use of the 604 processor. In addition, PCI peripherals will cost less and give you higher performance.
PRODUCT INFORMATION
Power Mac 9500
with a 132-MHz 604,
16 MB of RAM, and a 2-GB hard drive $5799
with a 120-MHz 604,
16 MB of RAM, and a 1-GB hard drive $4999
Apple Computer, Inc.
Cupertino, CA
(800) 776-2333
(408) 996-1010
fax: (408) 974-6412
illustration_link (5 Kbytes)
Running BYTE's Native Performance Benchmark at similar clock speeds, the PowerPC 604's integer performance is 87 percent faster than that of a 133-MHz Pentium machine, and floating-point performance is 72 percent faster. We used Motorola's latest PowerPC libraries to compile the test.
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The Apple of your dreams: a 132-MHz 604-based Power Mac.
Tom Thompson is a BYTE senior technical editor at large with a B.S.E.E. from the University of Memphis. He is also an Associate Apple Developer. You can reach him on AppleLink as T.THOMPSON or on the Internet or BIX at
tom_thompson@bix.com
.
Power Mac Gets PCI
