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The Power Macintosh Hardware
Its not just the PowerPC chip which makes a box a Power Macintosh
By Jordan Mattson, Apple Computer Inc.
Power Macintosh Introduction
On March 14, 1994, Apple Computer finally unveiled the Power Macintosh to the world in a gala event at Lincoln Center in New York City. At this event over three years worth of labor by the members of the Rock & Roll team - Apples code name for the Power Macintosh program - saw the light of day and once again raised the bar for personal computing.
For those of us that have worked on the Power Macintosh, it was a day filled with relief and excitement. Relief at completing a long and difficult journey, at completing a difficult and challenging task. And excitement at seeing the worlds reaction to our baby. For this column, it also means that we can start discussing the Power Macintosh in greater detail; a level of detail that we could not go into previously because of the restrictions of our confidentiality agreements with Apple. In the months ahead we will dig more deeply into the hardware and system software of the Power Macintosh, as well as go into how to create applications that take advantage of the Power Macintosh.
This month, we start delving into the details of the Power Macintosh by taking a tour of the Power Macintosh hardware.
The Power Macintosh Family
The Power Macintosh family consists of six systems:
Power Macintosh 6100/60
Power Macintosh 6100/60AV
Power Macintosh 7100/66
Power Macintosh 7100/66AV
Power Macintosh 8100/80
Power Macintosh 8100/80AV
Unlike previous Macintosh names, which may or may not have told you something about their construction, the Power Macintosh names clearly tell you a lot about them.
The first digit of a Power Macintosh model number (in this case 6, 7, or 8) tells you the form factor. Models starting with 6 are in the Quadra 610 pizza box while models starting with 7 are in Quadra 650 box bread box; and finally models that start with an 8 are in a Quadra 800 mini-tower.
The next three digits of the model number tell you the processor in your Power Macintosh. A 100 indicates a PowerPC 601 microprocessor. How future models of the Power Macintosh family that use future members of the PowerPC family of microprocessors will be identified is left as an exercise for the reader.
The final part of a Power Macintosh model number, the numbers after the slash, identifies the speed at which the chip is operating. For example, the Power Macintosh 6100/60 runs the PowerPC 601 at 60 MHz, while the Power Macintosh 8100/80 runs it at 80 MHz.
Finally, AV configurations of the Power Macintosh family are indicated by the addition of an AV suffix to the product name. All Power Macintosh systems support the high-quality sound, speech input, speech synthesis, and telephony features of the original AV systems. AV Power Macintosh systems also support video capture and output features.
The only difference between a standard Power Macintosh system and an AV Power Macintosh is the addition of the AV card. The AV card is not available as an after-market option, but only comes bundled with a Power Macintosh AV system. The features of the AV card are discussed in the section AV Features - Video.
The Birth of a New Generation
The Power Macintosh 6100, 7100, and 8100 are the first members of the next generation of Macintosh - the first step in the evolution of Macintosh on a RISC platform. Therefore, the features and architecture of the Power Macintosh systems discussed here should not be in any way, shape, or form be considered the final step in the evolution of Macintosh. In fact, in many ways, the first Power Macintosh systems can be thought of as the missing link between the world of 680x0 based Macintosh systems and the PowerPC microprocessor-based Macintosh systems of tomorrow.
The Soul of a New Generation
The soul of the new Power Macintosh systems is no surprise to anyone, the PowerPC 601 microprocessor from IBM, Motorola, and Apple. Around this soul the Power Macintosh hardware engineers have constructed a supporting architecture that allows the system software and applications to tap the performance of the PowerPC, while maintaining a very high-level of compatibility with previous Macintosh systems. Therefore, in many respects the hardware architecture of the Power Macintosh family is just a Macintosh. The significant changes in the Macintosh hardware - and system software - will come with the next, and later, generations of Power Macintosh systems.
The members of the Power Macintosh family are identified by Gestalt using the identifier gestaltMachineType. These values are as follows:
System Gestalt Value Identification Code
6100/60 and 6100/60 AV $4B 000
7100/66 and 7100/66 AV $70 010
8100/80 and 8100/80 AV $41 011
All members of the Power Macintosh family have a 4MB ROM. While some of this additional ROM space is required to deal with the code bloat associated with moving to a RISC architecture, much of it was used to put system code that used to be on disk and loaded into RAM into ROM. This reduces the amount of RAM required for the system, and hence makes more RAM available for applications. In addition, 560K of the ROM is taken up by the 68LC040 emulator.
The ROM for Power Macintosh family systems has a 120 ns initial access time, and then a 60ns burst access for following accesses. Since a 601 cache burst contains four 64-bit words, this means that the first word takes 120ns, and the following three all take 60ns, for a total of 300ns. This averages to 75ns if you care to look at it that way. The ROMis mounted on a SIMM card, so its theoretically possible to upgrade the ROM in a Power Macintosh by replacing the SIMM card.
All Power Macintosh systems accept standard 72 pin RAM SIMMs that have an access time of 80 ns or better.
Unlike the Quadras, RAM must be installed into Power Macintosh systems in matching pairs with each pair occupying a single bank. Unlike the Macintosh IIci and other systems, there is no requirement that the RAM be placed into banks in a particular order., although there is a two-at-a-time rule because the SIMMs are 32 bits wide, and the DRAMbus is 64 bits wide (theres been a lot of confusion on the nets on this issue, but this is the real reason).
The maximum size RAM SIMM that will be accepted by a Power Macintosh system is 32 MB.
The following table outlines the RAM expansion capabilities of the Power Macintosh family:
System On Board Maximum Number of
RAM RAM RAM Slots
6100/60 8 MB 72 MB 2
6100/60 AV 8 MB 72 MB 2
7100/66 8 MB 136 MB 4
7100/66 AV 8 MB 136 MB 4
8100/80 8 MB 264 MB 8
8100/80 AV 8 MB 264 8
The PowerPC 601 microprocessor has an 32 KB onboard cache. In addition, all Power Macintosh systems can support a level 2 cache, and common sizes are 128 KB or 256 KB. Apple is only offering a 256 KB level 2 cache. This cache is pre-installed on the 8100/80 and 8100/80 AV. The cache design is independant of size, so you could make a 32MBcache if you wanted and if you could fit all the chips on a SIMMthat is about 1 x 4.
On average the presence of a 256 KB level 2 cache boosts system performance by around 0% to 40%, averaging about 20%. Of course the actual benefit from a level 2 cache depends on the software being run and its cache hit rate.
I/O - Video
All Power Macintosh systems have on-board video support for 12, 13", 14, portrait, VGA, and 16" monitors using system memory as a frame buffer; 13" monitors can have a depth of up 16 bits, while 16" monitors can have a depth of up to 8 bits. The connector for on board video is an HDI-45. If you want to connect the onboard video to anything other than the Apple AudioVision display, you will need to use a special adapter cable that has an Audio HD-45 plug at one end and a DB-15 plug at the other end.
In addition to the on-board video support on all Power Macintosh systems, the 7100/66 and 8100/80 come bundled with a VRAM based frame buffer that provides a second video output using a DB-15 connector. Therefore, both the 7100/66 and the 8100/80, straight from the factory, are capable of supporting two monitors.
Contrary to what you might think, the VRAM based frame buffer used by the 7100/66 and the 8100/80 are not the same card! Not only are they different cards, they use different SIMMs. Whereas the 7100/66 VRAM based frame buffer uses SIMMs with two 128k by 8 bit chips; the 8100/80 VRAM based frame buffer uses four 256k by 4 bit chips.
The Power Macintosh AV configurations - the 6100/60 AV, 7100/66 AV, and 8100/80 AV - come bundled with an Apple AV card which in addition to supporting video in and out, provides 2 MB of VRAM (nonexpandable) to the Power Macintosh AV systems and makes them also capable of driving a second monitor using a DB-15 connector.
The monitor support provided by the various Power Macintosh configurations is summarized in the following table:
Video Option 6100/60 7100/66 8100/80
DRAM 16 bit on 14" 16 bit on 14" 16 bit on 14"
8 bit on 16" 8 bit on 16" 8 bit on 16"
VRAM - 1 MB N/A 16 bit on 16" N/A
8 bit on 21"
VRAM - 2 MB N/A 24 bit on 16" 24 bit on 16"
16 bit on 21" 16 bit on 21"
VRAM - 4 MB N/A N/A 24 bit on 21"
AV Card 24 bit on 16" 24 bit on 16" 24 bit on 16"
16 bit on 21" 16 bit on 21" 16 bit on 21"
I/O and DMA
To minimize interrupt off time, Direct Memory Access (DMA) is supported for Ethernet, sound, SCSI, the floppy, and serial I/O (including GeoPort). This support is provided by the Apple Memory-Mapped I/O Controller (AMIC).
I/O - Sound
All members of the Power Macintosh family support simultaneous 16-bit stereo sound input and output. This quality of sound input and output is required to support PlainTalk speech recognition software and to give the highest quality speech synthesis.
I/O - SCSI
All members of the Power Macintosh have two SCSI connectors: a 50-pin ribbon connector for internal devices and a DB-25 connector for external devices. With a maximum data transfer rate of 5MB per second, the standard SCSI bus is completely compatible with the SCSI bus on other members of the Macintosh family. Its basically the same SCSI system as in the 660AV and 840AV Macs.
Termination of the external end of either the standard SCSI bus on the Power Macintosh is handled as it is on all Macintosh computers, by placing a terminator on the last external device. The internal end of the standard SCSI bus is terminated by a terminator in the last internal SCSI device. Therefore, the last SCSI device installed in a Power Macintosh system must be properly terminated. If no external device is connected to the standard SCSI bus, the external portion of the SCSI bus will be automatically terminated.
In addition to the standard SCSI bus provided on all members of the Power Macintosh family, the 8100/80 and 8100/80 AV have a second fast SCSI bus. This fast SCSI bus can transfer data at 10 MB per second, and is automatically terminated if no devices are connected to it. When shipped from the factory, the internal drive on 8100/80 and 8100/80 AV systems is connected to the fast SCSI bus.
Internal SCSICD-ROM drives are connected to the external bus internally.
The Asynchronous SCSI Manager (officially known as SCSIManager 4.3) is supported on all members of the Power Macintosh family.
I/O - Floppy
The floppy drive in all members of the Power Macintosh is a new version of the SuperDrive that, like the SuperDrives on the PowerBooks, does not support auto-inject. It supports both Group Code Recording (GCR) format and Modified Frequency Modulation (MFM) format for reading DOS/Windows compatible disks. [If you cant stand the new drive, try swapping it with an auto-inject drive from one of your other machines - Ed stb]
I/O - Serial and GeoPort
All Power Macintosh systems have two serial ports. Either port can programmed for asynchronous or synchronous communication at up to 57600 baud, to support LocalTalk, or to run the GeoPort protocols (about 2Mbps). Therefore, with the addition of a GeoPort Pod, a Power Macintosh can support the telephony features of the AV Macintosh systems.
AV Features - Audio
As discussed above, all Power Macintosh systems support the audio features of Apples suite of AV technologies. This means that you can do speech recognition, speech synthesis, and high-quality - 16-bit stereo - sound sampling and playback on a Power Macintosh system. The Power Macs support 44.1kHz and 22.05kHz. The 660 and 840 supported two additional rates of 24kHz and 48kHz, but these rates are not supported by Power Macintosh.
This level of support for audio input and output is the new base level for Macintosh systems and Apple plans on supporting it in all future Power Macintosh systems.
AV Features - Video
The Power Macintosh systems, with the addition of the PDS-based AV Card, offer the video features of Apples suite of AV technologies. With an AV-equipped Power Macintosh, you can input and output video signals and intermix video and graphics on your display. In addition, you can drive a second monitor, as described in the section I/O - Video.
The AV Card supports the input and output of both composite and S-Video signals. The AV Card can accept as input video signals in NTSC, PAL, and SECAM formats; and it can output video signals in NTSC or PAL format. For connecting to a video monitor, the AV Card sports a standard DB-15 connector.
In addition to its various video input and output connectors, the AV Card also has a DAV - digital audio/video - interface. The DAV connector - which first appeared on the Macintosh Centris 660AV and Quadra 840AV - provides direct access to the audio and video signals of a Power Macintosh system. The DAV connector can be used on the Power Macintosh 7100/66 AV and 8100/80 AV to give NuBus cards direct access to audio and video signals. This is not a option on the 6100/60 AV, since the single slot available on the 6100/60 is occupied by the AV Card.
As we mentioned above, the AV Card can intermix video and graphics. This is achieved by configuring the 2 MB of VRAM on the AV Card into two 1 MB frame buffers. One for video and one for graphics. The video images from these two frame buffers are fed via VRAMs serial access memory port to the Sebastian color palette chip. The Sebastian chip then combines the video images and graphics images into a single digital RGB data stream and converts the resulting data stream into an analog RGB video signal. The resulting analog RGB signal can either be fed directly to the monitor or encoded into NTSC or PAL format and output as composite or S-video.
The Power Macintosh AV systems come configured from the factory with an AV Card. The AV Card cannot be purchased separately, therefore you have to decide at the time of purchase if you want an Power Macintosh AV system or not.
Expansion Capabilities - PDS
All of the Power Macintosh systems sport a PowerPC 601 processor direct slot. This bus give direct access to the standard 64-bit nonpipelined bus of the PowerPC 601.
Except in the case of the Power Macintosh 6100, the PDS slot is occupied when shipped. With an AV Card - in the case of AV systems - or a VRAM based frame buffer in the case of the 7100/66 and the 8100/80.
On the 7100/66, 7100/66 AV, 8100/80, and 8100/80 AV, unlike other Macintosh systems that in the past that mixed PDS cards and NuBus cards, you do not lose access to a NuBus slot when you have a PDS card resident.
Since the PDS slot on most Power Macintosh systems is filled, it probably does not make a lot of sense to design expansion cards that utilize this slot. Rather you should consider the PDS slot more Apples way to deliver expanded functionality to the base systems. This is not to say that you cant use the PDS slot - it is fully documented - but rather that Apple is fully utilizing it in most shipping systems.
Expansion Capabilities - NuBus
All of the Power Macintosh systems, except for the 6100/60 AV, can accept NuBus cards.
The 6100/60 can accept a single 7" NuBus after the addition of a NuBus adapter card similar to the one found on the Macintosh IIsi. The 6100 NuBus adapter maps the appropriate signals to one another and provides a BART NuBus controller.
The 7100/66, 7100/66 AV, 8100/80, and 8100/80 AV can all accept 13" and 7" NuBus cards.
While NuBus on the Power Macintosh is not a full implementation of the NuBus 90 standard, it does support block transfers to and from memory as well as supporting double speed block transfers between cards.
As you will notice by comparing the block diagrams of the 6100/60, 7100/66, and 8100/80, the base system architecture of the first generation of the Power Macintosh family is provided by the 6100/60. The system architecture of the 7100/66 and 8100/80 are built by adding various features to the 6100/60s architecture.
As you can see by comparing the block diagram for the 7100/66 to that of the 6100/60, the system architecture for 7100/66 is created by adding the BART NuBus controller and three NuBus slots to the base Power Macintosh architecture provided by the 6100/60.
The pinnacle of Power Macintosh performance is built on the base provided by the 6100/60 by adding the BART NuBus controller, three NuBus slots, and a second internal Fast SCSI channel.
Block Diagram Tour
This section is a brief overview of the major functional units on the Power Macintosh logic board.
The AMIC - Apple Memory Mapped I/O Controller - controls most I/O on the Power Macintosh Systems. It performs the following functions:
Handling of interrupts received through the VIA channels
DMA for Ethernet, the SWIM III floppy controller, serial communications, SCSI, sound I/O
And support for onboard video
Block Diagram - 6100/60
Ariel II Video Chip
The Ariel II video chip provides a color lookup table and a digital-to-analog converter to drive monitors connected to the AudioVision port.
AWAC Sound Chip
The AWAC - Audio Waveform Amplifier and Converter - sound chip is a combined waveform amplifier and 16-bit digital sound encoder and decoder.
BART NuBus Controller
The BART NuBus controller is the data gateway between NuBus and the Power Macintosh processor bus. It acts as the CPU bus master and is fully complaint with the IEEE 1196 NuBus standard. Its functionally identical to the MUNI chip in the 660 and 840.
Cuda Microcontroller Chip
The Cuda microcontroller manages system functionality, including turning system power on and off, resetting the system based on various commands, maintaining parameter RAM, servicing ADB, maintaining the real-time clock, and responding to system power on or off commands from GeoPort.
Block Diagram - 7100/66
Block Diagram - 8100/80
Curio I/O Chip
The Curio I/O chip combines the Ethernet controller, SCSI controller, and the Serial Communications Controller in a single chip.
Data Path Chips
The Data Path chips provide buffering between the I/O controllers and DRAM and the CPU bus. They also provide FIFOing of the video data from the DRAM to the Ariel for the on-board video support.
The HMC - High-speed Memory Controller- manages all memory operations. In particular, it provides the following features to support data transfer between the processor and the rest of the system:
Support for all basic memory transfer protocols
Support for four-cycle 32-byte cache accesses
Automatic translation of misaligned reads into double-word reads. Actually, it would, but the 601 already does this.
Implementation of address-only transactions
On the 6100 it handles bus arbitration. For the 7100 and 8100, there is an extenal chip which does bus arbitration. It was added to handle the additional bus master (NuBus as well as PDS) for those machines.
The Squidlet chip provides the clock for both the processor and the CPU bus. The following are the specific clock frequencies for the Power Macintosh family system clocks:
System Processor Clock CPU Bus Clock
6100/60 and 6100/60 AV 60 MHz 30 MHz
7100/66 and 7100/66 AV 66 MHz 33 MHz
8100/80 and 8100/80 AV 80 MHz 40 MHz
The SWIM III floppy disk controller is an evolution of the SWIM II floppy controller. The SWIM III chip supports the following new features:
DMA for the floppy drive
No longer requires that interrupts be disable during floppy disk access
Support for both GCR and MFM formats on 1.44 MB disks
Support for manual-inject floppy drives
For More Information
If you are interested in a detailed discussion of the details of the Power Macintosh hardware, you should check out the Power Macintosh Computer Developer Note. This developer note is available on the Developer CD and from APDA. The Power Macintosh Computer Developer Note, along with internal Apple Engineering specifications were the primary sources for this article. [Special thanks to two excellent definitive resources who double-checked the details and provided some enlightening explanations - Ed stb].
Next Month in Powering Up
With the introduction of the Power Macintosh, we are now free to start digging into the system details of the Power Macintosh. Starting next month, we will be exploring how to exploit the features and performance of the Power Macintosh to create new classes of applications.