Technical Q&A HW32

Differences between iMac models

Q: What are the differences between the iMac rev A, B & iMac 266 models?

A: There are a number of changes among the three revisions the iMac that are relevant to Mac developers. The first iMac (rev A) was built with a different logic board than the Rev B and iMac 266 models.

As far as actual part numbers are concerned, the iMac 266 is not classified as a revision C; it is actually a revision A product and has been assigned new part numbers (one for each color).

Part numbers

Mezzanine Connector

Earlier iMac models (revision A & B) included an internal connector that some sources referred to as the Mezzanine connector. This connector was intended for Apple's initial internal development and manufacturing purposes, and was never at any time supported for third-party development. Thus, it has been removed from the logic board.

Floppy support

The iMac revision A & B had provisions for an internal floppy disk connector that was intended for initial internal development and manufacturing purposes. This connector and associated ROM code was never supported for third-party development and thus was also removed from the logic board.

Floppy drives are, however, supported as USB peripherals and available from a number of third parties. Note: The currently version of USB software does not support booting from a floppy device.

IrDA

The iMac 266 has removed the IrDA port. However, IrDA is still very important for portables, but their usage and user requirements are different from desktop Macs. In addition, due to the success of USB, Apple has decided to focus on USB as the primary method of connecting peripherals to desktop computers.

Graphics Acceleration Hardware

The iMac rev A was shipped with the ATI RAGE IIc graphics controller and 2 MB of video memory. The rev B & iMac 266 have been updated with the higher performance ATI RAGE PRO TURBO accelerated 2D/3D graphics controller and 6MB (2 MB Built-in + 4 MB DIMM) of video memory.

RAM

There are no changes to iMac memory expandability between models.

USB

Revision A iMacs were shipped with USB 1.0, while revision B iMacs shipped with USB 1.0.1. "iMac Update 1.0" can be used to update rev A iMacs to USB 1.0.1. The 266 Mhz iMacs feature USB 1.1.

USB 1.1 fixes several significant bugs in the notification of new devices, as well as improves the robustness of hot-plugging. The USB 1.1 kit installs Zip and SuperDisk drivers, Game Sprockets (which includes drivers for about a dozen controllers/joysticks). USB 1.1 also includes the HP and Epson printer drivers in CD Extras folder.

Both Revision A and B iMacs can be upgraded to USB 1.1 with "iMac Update v1.1". Note that in order to use this update on a Rev A. iMac, Mac OS System Software 8.5 must be present.

System Software

Below is a table of system software shipped with each revision of iMac.

Specifications

The latest spec sheet for the iMac can be found at the iMac specification page.