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					                                                                                                                 MAC




                                                                                                                       TECHNOL OGY
               iMac:
   Shades of thePC?
                                                                                    Behind the stunning
T
        he iMac is different from a PC.   all we had were the labels on the board
        That’s a no-brainer. But have     and the ICs. But after hours of poring
        you asked—how different? We       over obtuse chip-design and interface
                                                                                    design, the iMac has
know about the different processor, the   specifications, downloaded from           quite a bit in common
PowerPC, and the different operating      equally obtuse places on the Web, we
system. The iMac even opens up
                                                                                    with Intel desktops
differently—it opens up from the
bottom. And your online
MacOS help gives you
detailed instructions on
how to open it. Just
open Help and search
for “adding RAM” to
get to it.
    But beyond that?
    At PCQ Labs, we
spent quite a bit of
time tearing open
one of the first iMacs
to land in this country
(Apple for sure is not
going to be amused).
And ended up with a
circuit board barely
                                                                                       Barring the monitor and
larger than my palm. This                                                              the power electronics,
is the L ogic Board, the                                                               most of the iMac is
                                                                                       housed in this carousel
Macintosh equivalent to the
motherboard. To lead us from here
                                Bottom up view of the logic board
                                                                    No prizes for
                                                                    guessing this one.
RJ-11 jack for
                                                                    The modem is based
your telephone
                                                                    on the all too familiar
cable (seen from
                                                                    Rockwell chipset
the
other side)
                                                                          The modem card
                                                                          connects to the logic
                                                                          board here


Programmer’s                                                                The Mezzanine
button—                                                                     port. Now what’s
you would                                                                   this? Nothing
probably                                                                    much is known
never need                                                                  about this port. A
to use it                                                                   bit of hunting
                                                                            yielded the
                                                                            following informa-
                                                                            tion. Also called
                                                                            Perch slot, the
                                                                            MacWeek magazine
                                                                            (http://
                                                                            macweek.zdnet.
                                                                            com/1232/
This extra-                                                                 mezzanine. html)
narrow                                                                      speculates that this
daughter                                                                    could be a future
card is the 56                                                              expansion option
kbps modem                                                                  following the PCI
                                                                            mezzanine card
                                                                            specification




                   The iMac logic board beats
                   Baby ATX motherboards in
                   size




               A different view of the
               logic board carousel.
            Removing the side plate
                  for the connectors
                 reveals some empty
             space. This is probably
              for future expansion—
            the mezzanine port is at
                        the other end
                                                                    Space saver—the
                                                                   CD-ROM drive fits
                                                                       on top of the
                                                                           hard disk   Unlike conventional PCs, you
                                                                                       have to open up the iMac from the
                                                                                       bottom. Removing one screw and
have the iMac story for you.                      The rest as you have seen in these   a molded plastic cover reveals the
    Traditionally, Macs have used SCSI as     pages is more PC than classic Mac. Oh!   logic board assembly. You need to
                                                                                       remove two more screws to get
their data interface—SCSI hard disks,         one more thing. The iMac keyboard and    this out. (In the lower half, you
SCSI ports… That is now passe. Similarly,     mouse, both will work fine with your     can see the hard disk)
the Apple Desktop Bus (ADB), which was        Windows PC. They are USB peripherals
used to connect keyboards, mice and the       after all.
like is also history. In its place you have       One of the many iMac ads says
PCI and USB. PCI and USB? Yes. The very       “iMac…the most un-PC as you can get.”
same PCI and USB you have on your PC.             Are you sure?
And that is not all. You have an IDE hard                              Krishna Kumar
disk that would be equally at home on
your PC—a Quantum Fireball—and an
ATAPI CD-ROM drive.
    So, is the iMac really more of a PC
than a Macintosh?
    To be fair to Apple, Macintoshes have
been shipping with PCI interfaces and ATA
hard disks for quite some time now. The
PowerMac we brought at PCQ Labs about
two years ago was one such.
    What really sets the iMac apart is a
stunningly new approach to industrial
design. Its various elements—the logic
board, the monitor, the modem, and the
sound card…fit into an extremely                                                                  This fan keeps the
compact, all-in-one unit. And unlike the                                                          CPU cool. The hot
                                                                                                  air is expelled
PC, the processor or the daughter cards                                                           through the top of
don’t gobble up all the space.                                                                    the machine

				
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