An Introduction to Macintosh Hardware

Processors - 68K and PowerPC
From 1984 to the early 90s, all Macintosh computers were equipped with a Motorola chip, the 680x0 line. They initially started with the 68000, then progressed to the 68020, 68030 and 68040. These numbers are merely the designation of the chips: the higher the number, the faster the chip. The 680x0 chips were CISC (Complex Instruction Set Computing) processors. Then, in the mid-90s, Motorola introduced a relatively inexpensive and easy to produce RISC (Reduced Instruction Set Computing) chip which would allow tremendous increases in speed over the 68k line: the PowerPC chip. The PowerPC began appearing in Macintoshes soon after and now every new model of Macintosh has a version of these PowerPC chips (601, 603x, 604x). Newer versions of the chip have become commonly known as the G3 processor and the G4 processor. The G3 and G4 computer lines are named after these chip, which were optimized specifically for MacOS (PowerPC chips were originally intended as a standard for multiple operating systems). G3 and G4 processors can also be found in iMacs, iBooks, PowerMacs and PowerBooks.

PowerMacs can run in two different modes: native mode, when running software written to use the PowerPC processor directly, or emulation mode, when running software written for the 68K processors. The computer can switch between modes as needed and the switch is invisible to the user. Most applications have been ported to PowerPC and MacOS 8.0 and above is written completely in PowerPC native code.

PowerPC applications require significantly less memory if Virtual Memory is turned on (because of caching and disk operations), so it is recommended to always turn on VM on a PowerPC Mac, even if it is set to the lowest value.

Ports

• SCSI
  Older Macintosh computers come equipped with a special port called a SCSI port. Pronounced 'scuzzy,' the acronym stands for Small Computer System Interface. SCSI is a flexible, high-speed port used by the Macintosh to attach such devices as hard drives, scanners, CD-ROM drives or ZIP drives. Since most Macs have only one SCSI port, multiple devices are added by "daisy-chaining" them together. SCSI chains can contain at most 8 devices, including the hard drive and the Macintosh itself. Each device must have its own unique SCSI ID number between 0 and 7, configurable by a hardware switch on the device. The last device in the chain must be terminated with a special plug to signal the end of the chain.

  Newer Macs have replaced the SCSI ports with USB and/or FireWire ports, to be covered later in this section. SCSI devices can often still be connected to these machines using a SCSI PCI card and cable adapter.

  Earlier Macintosh hard drives are usually SCSI by nature. They are part of the SCSI chain and usually have SCSI ID 0. (The Macintosh usually has SCSI ID 7.) Most recent models carry IDE (Integrated Device Electronics) internal drives, which are commonly used in PCs. IDE drives are somewhat slower, but a significantly cheaper alternative to SCSI drives. They do not occupy a place in the SCSI chain, but are attached independently to the computer.

  For most concerns, IDE and SCSI hard drives may be treated the same; the only difference is with formatting, because some utilities will only work with one or the other.
  
  

• ADB
  The ADB (Apple Desktop Bus) is a special port found on most Macs and is used to connect input devices such as the keyboard and mouse. The ADB port looks very similar to a serial port, but has a different pin configuration; the icon above it is a three-pronged image. The ADB is powered, so any device plugged into it is powered. Any device connected to the ADB port should NOT be disconnected or reconnected while the computer is on. There is a slight power surge effect whenever a device is connected or removed, which could severely damage the device or the computer.
  
  
• Printer and Modem
  Most of the older Macintoshes (except for some PowerBooks) come equipped with two identical serial ports: a printer port and a modem port. These ports are used to connect LocalTalk devices (printers, other computers), external modems, QuickDraw printers and other serial devices.

  Some computers have an internal modem installed, which disables the modem serial port. Also, if you have AppleTalk turned on and it is using one of the serial ports as a LocalTalk port, then that port is disabled for other functions.

  Like SCSI ports, these serial ports are disappearing in favor of USB ports, FireWire ports and PCMCIA slots.
  
  

• USB and FireWire
  USB (Universal Serial Bus) is a newer technology port which can connect up to 127 peripheral devices and supports data transfer rates of up to 12 Mbps. USB was developed in 1996, but did not become very popular until the release of the iMac in 1998. USB is rapidly replacing serial and parallel ports both on Macs and PCs. USB devices are "hot-pluggable," meaning you can add a new device without having to restart the computer. Newly developed USB 2.0 ports have the same functionality as the older USB ports but provide the capability for data transfer rates of up to 480 Mbps.

  FireWire is an even newer peripheral standard originally developed by Apple, mainly for high-speed multimedia peripherals such as video camcorders. FireWire can support up to 63 devices per machine and most new Macs ship with at least one FireWire port, capable of communicating at speeds of up to 400 Mbps. Like USB devices, FireWire devices are "hot-pluggable." The name FireWire has been trademarked by Apple, but the "generic" name for the standard is IEEE 1394. For more information, please visit:
  FireWire Home Page
  
  

• Ethernet
  Since the inception of PowerMacs, almost all Macintoshes have come equipped with a built-in ethernet port. The ethernet port itself is usually a somewhat rectangular port (much like a modem port, but larger), with a single arrow pointing in both directions next to it, like this: <-->.

Floppy Drive
Although the iMac and G4 do not have floppy drives, there are still plenty of Macs that do have them. The very earliest Macintoshes came with only a floppy drive, a 400K 3.5" drive. Macs were the first mass-marketed computer to use the 3.5" disk, a vast improvement over 5.25" floppies.

It's important to note that Macs can read both PC- and Macintosh-formatted floppy disks; PCs can only read PC-formatted floppies.

Plug-and-Play
One of the Mac's core technologies is Plug-and-Play. This technology greatly simplifies the installation of new hardware. Macs have a built-in system which allows the hardware to communicate with the computer and coordinate the configuration, so there are usually no conflicts.