Macintosh Hardware
Volume Number: 10
Issue Number: 5
Column Tag: Powering UP
Related Info: SCSI Manager
The Power Macintosh Hardware 
It’s 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 - Apple’s 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 world’s 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.
True Names
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 È$4B 000
7100/66 and 7100/66 AV È$70 010
8100/80 and 8100/80 AV È$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 it’s 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