Using Internal Interfaces

There are numerous types of internal interfaces you will never deal with?unless you build your own Mac or do complex repairs. However, some of the internal interfaces are important to understand because you use them to expand your system.


The AT attachment (ATA) interface is a PC standard specification for hard disk drives and has been adopted on modern Macs. The ATA interface provides high-speed communication, and because it is a PC standard, ATA hard drives are inexpensive.

As with other specifications, there are various "flavors" of the interface, with each offering a specific speed. For example, modern PowerMac G4s use the Ultra ATA/100 standard, which means the throughput of devices using this standard is 100 megabytes per second (MBps). If you add internal hard drives to a Power Mac G5 or PowerMac G4 or replace an existing drive with a larger one, make sure the drive uses the ATA standard your Mac supports.


When you deal with internal devices, you might also hear the term IDE, which stands for integrated drive electronics. IDE devices are those on which the controller is integrated into the device rather than provided by the computer. This term is often used as a synonym for ATA because ATA devices are also IDE devices. But IDE refers to the general technology, whereas ATA refers to a specific specification.


If your Mac supports FireWire 400 or 800, it is often better to add an external FireWire drive than to add more internal drives.


The dual inline memory module (DIMM) interface is the standard for RAM chips in many modern Macs, such as the Power Mac G4. DIMM chips use a 64-bit path. You use this interface when you want to expand the RAM capability of one of these Macs.

PowerBooks and iBooks use small outline DIMM (SODIMM), which is a physically smaller interface that provides the same capabilities as the full-size DIMM.

The newest Macs, such as Power Mac G5s, use double data rate synchronous dynamic random access memory (DDR SDRAM) modules. This technology offers improved performance over previous Mac models.

In all cases, when you expand your Mac's RAM (which is one of the best things you can do), you need to ensure that you get memory modules that are the type and speed your Mac supports. See your Mac's documentation to determine the type of memory modules you need for it.


Earlier in this chapter, you read that SCSI was once a standard external interface. Because of its speed advantages, it was also a standard internal interface that was used for all Mac hard drives. In fact, Apple was the only manufacturer that included the SCSI interface and drives as standard equipment. This speed advantage was one reason the Mac became popular with graphics professionals and others who needed to move a lot of data quickly.

In an effort to cut the cost of its machines, Apple did away with the SCSI interface as the standard one for internal data communication. At the same time, the speed of the PC standard interface, ATA, increased such that this imposes little to no performance penalty for modern Macs. (FireWire replaced SCSI to connect external devices.)

There is more than one SCSI standard, each of which offers a specific speed along with other specifications. Some examples are the following:

  • Fast SCSI? Supports speeds up to 10MBps

  • Ultra SCSI? Supports speeds to 20MBps

  • Ultra Wide SCSI? Supports speeds up to 40MBps

The various SCSI specifications use various connectors and cables?you usually can't connect a device using one standard to an interface that uses another. As with other interfaces, the actual speed of communication across a SCSI interface defaults to the maximum speed of the lowest-speed device connected to the interface.

    Part I: Mac OS X: Exploring the Core
    Part III: Mac OS X: Living the Digital Life