This article contains the Read Me for the iMac Firmware Update 1.1, as well as other relevant information. This software was released by Apple on 18 December, 1998 and is available for downloading from the Apple Software Update web site at http://www.apple.com/swupdates .

iMac Firmware Update is based on customer feedback, and increases the reliability of iMac booting. It is being provided to every iMac customer as preventive maintenance. The iMac Firmware update upgrades the Open Firmware boot ROM code using a simple application downloadable from Apple's web site.

Who needs the iMac Firmware Update?
Every iMac customer should install this update. This update will only install on iMac computers.

What are the requirements for installing iMac Firmware Update?
This update can be installed on any iMac worldwide. Currently, the instructions for installing are available only in U.S. English but localized installers will be available soon for other languages, including International English, Spanish, German, French, Swedish, Italian, Japanese. Steps were taken to make this update as simple as possible so that most iMac customers worldwide could download and install this version.

What specifically does iMac Firmware address?
The update provides three enhancements:

1. Enhanced file system support
The new firmware supports all of the extent and extent overflow fields of the HFS/HFS+ file structure. Without this, it was possible for the Mac OS ROM file to stored in the extent and extent overflow fields of the HFS/HFS+ file structure which would prevent the iMac from starting up. In cases where this occurs, all of the data on the hard disk is still preserved, but the iMac won't be able start up from the hard disk until the iMac Firmware updater is run. This issue is extremely rare, but certainly important to address.

2. Dual-image boot ROM
The iMac Firmware update installs a second boot ROM image within the flashable ROM. Should there ever be a future firmware update, the second image serves as a backup should the firmware update fail. Although a firmware update failure is highly unlikely, providing the second image would allow the iMac to start up.

3. Hardware protection
After installing the iMac Firmware Update, Rev/A iMac computers will be hardware protected against unintentional firmware updates. Like iMac Rev/B units, the NMI Programmer button or Interrupt button will need to be depressed (using a paperclip) prior to starting up iMac to enable the firmware to be updated. This prevents a firmware update from occurring unintentionally.

How do I obtain the iMac Firmware Update?
Apple is providing iMac Firmware Update at no charge through the Internet. It can be downloaded from the Apple Software Update web site at http://www.apple.com /swupdates .

Will Apple be delivering iMac Firmware Update on CD-ROM?

No. Customers should obtain the update through Apple's Software Updates web site.

How large is the downloadable iMac Firmware Update file?
The update is provided in compressed format and incorporates a self-check mechanism to verify that the file has been downloaded completely and without error. The compressed downloadable file is about 1 MB in size.

How to Install the Firmware Update

The following instructions are included in the Read Me file for the Firmware Update. Depending upon if you have a /A or /B iMac, there is one key difference in how you install the update: /B iMac customers must use a paper clip to depress the iMac Programmer's button for approximately five seconds after restart. A long tone will sound at which time the Programmers button may be released.

An alternative to a paper clip is the iReset, described in article 59010: " Macs Only! "

Note : After you upgrade the firmware, the PRAM will be reset which may require you to reset some iMac preferences. Refer to the Mac OS Help for details about what items will need to be reset. For example, you need to open the Startup Disk control panel and reslect your hard disk.

1. Double-click the iMac Firmware Updater icon to start the update.

2. Read the onscreen instructions and follow them carefully.

3a. On a /A configuration, a message will appear explaining that your iMac's firmware needs to be updated. Click the Update button and follow any further on-screen instructions.

5. Open the port cover door on the right side of your iMac and insert the end of a straightened paper clip into the Programmer's button hole, the lower of the two small button holes.

7. When you hear a long tone, remove the paper clip. A progress bar will appear at the bottom of the screen as the update takes place.

8. After successfully applying the firmware update the iMac will, upon restart, momentarily display a flashing question mark transposed on a folder icon. Once the iMac has fully restarted, use the Startup Disk control panel to set the internal hard drive as the startup disk. This action is necessary to prevent delays during the startup process.

Error Checking Prior to the Installation

A number of conditions are required before the update will be performed. Failure to meet these conditions will result in an error condition indicated by on screen dialog boxes. Conditions which will prevent successful installation of the update are:

• If the updater file has been moved outside of the folder containing the update installer
• If the updater is used on a computer other than an iMac
• If a Mac OS error #123 occurs
• If the volume is locked
• If the firmware is not recognized
• If the hard drive has less than 2.5 MB of free space

Conditions that May Cause the iMac Firmware Updater to Fail

There are other conditions that may cause the updater to fail.

• If power is removed during the update, the Boot ROM may become corrupted and not retrievable. The processor board will have to be replaced.
• If a /A configuration is restarted using the paper clip by mistake, the update will not complete. Power must be pulled for 15 seconds and the update attempted again.

How to Determine If a System Has Already Been Updated

The Firmware Update installer will verify that the update is required before installing it and will display a dialog if the update is not required. If you are unsure if your systems have been updated, simply run the Update installer.