Name:         PowerPC Interrupt Extension
Version:      1.0
Released:     October 31, 1996
Description:  This system extension may improve reliability
and performance on Power Macintosh computers, PowerPC-based
Performa computers, Mac OS-compatible computers, and on
desktop computers upgraded with a PowerPC upgrade card. This
extension requires System 7.5.5.

The enclosed file is a self-extracting archive. To use,
download and double-click the downloaded file (this
decompresses it).

Path to this software:

  Apple SW Updates
    US
      Macintosh
        System
          Other System
            PowerPC Interrupt Extension
            PowerPC Interrupt Extension.sea

From the Readme:

PowerPC Interrupt Extension
Overview and Installation


What is the PowerPC Interrupt Extension?

This system extension may improve reliability and
performance on Power Macintosh computers, PowerPC-based
Performa computers, Mac OS-compatible computers, and on
desktop computers upgraded with a PowerPC upgrade card. This
extension requires System 7.5.5.

Who should install the PowerPC Interrupt Extension?

Apple recommends installing the PowerPC Interrupt Extension
for all customers who have installed System 7.5.5 Update on
a desktop Power Macintosh, PowerPC-based Performa, Mac
OS-compatible, or on a desktop computer with with a PowerPC
upgrade card.

What does installing the PowerPC Interrupt Extension do?

After installing the PowerPC Interrupt Extension, you may
notice improvements in reliability and stability. You may
have experienced your computer freezing for several seconds
before returning to normal operation, or completely freezing
and requiring a restart. This extension fixes one source of
this problem.

I have a PowerBook with a PowerPC upgrade card. Should I
install the PowerPC Interrupt Extension?

PowerBooks, both with and without the PowerPC upgrade card,
do not experience the problems resolved by the PowerPC
Interrupt Extension. Therefore, it is unnecessary for
customers with these computers to install the extension.

I have a Macintosh based on the 680x0 processor. Should I
install the PowerPC Interrupt Extension?

Macintosh computers with a 68000, 68020, 68030, or 68040
processor do not experience the problem fixed by the PowerPC
Interrupt Extension. Therefore, it is unnecessary for
customers with these computers to install the extension.

How do I get System 7.5.5 Update?

To use the PowerPC Interrupt Extension, you must have System
7.5.5 Update installed. You can download this update through
the Internet at http://www.support.apple.com/ as well as
through America Online (keyword: applecomputer) and
CompuServe (shortcut: GO APLSUP). You can also order this
update for $13 by calling the Apple Order Center at
1-800-293-6617 ext.1322.

Once I install the PowerPC Interrupt Extension, do I need to
do anything else?

No. The PowerPC Interrupt Extension works automatically once
you install it according to the installation instructions.

How do I install the PowerPC Interrupt Extension?

To install this extension follow these steps:

1. Locate the System Folder icon on your computerŐs hard
disk.

2. Drag the PowerPC Interrupt Extension icon onto the System
Folder icon.

3. Click on the OK button when you see the message
"Extensions need to be stored in the Extensions folder in
order to be available to the Macintosh. Put 'PowerPC
Interrupt Extension' into the Extensions folder?"

4. Select Restart from the Special menu for the changes to
take effect.

How do I disable the PowerPC Interrupt Extension?

To disable this extension follow these steps:

1. Select Control Panels from the Apple Menu.

2. Locate the Extensions Manager icon and double click it.

3. Scroll through the list until you see PowerPC Interrupt
Extension.

4. Click on the PowerPC Interrupt Extension name so that the
check mark beside it disappears.

5. Select Restart from the Special menu.


Technical Details

The following is provided for application developers and
others who are interested in the technical details of the
PowerPC Interrupt Extension.  You do not need to understand
the following information to use the extension.

The PowerPC Interrupt Extension applies a fix to the low
level interrupt services on desktop PowerPC-based Macintosh,
Performa, and Mac OS-compatible computers, and on desktop
computers upgraded with a PowerPC.  Before this fix, a
condition could exist where no interrupt was pending but the
computer would wait for an interrupt.  In this condition the
computer would ignore all lower priority interrupts and no
processing would continue until a higher or equal priority
interrupt occurred.  In some cases this would cause
intermittent, long interrupt latencies.  In other cases this
could cause the computer to freeze.

One condition which creates the problem is when a completion
routine or interrupt task lowers the current interrupt mask
value during its execution.  Installing the PowerPC
Interrupt Extension applies a fix which will prevent this
from causing a freeze or long interrupt latency.


Copyright 1996  Apple Computer. Inc. All rights reserved.
Apple,  the Apple logo, Mac OS and Macintosh are trademarks
of Apple Computer, Inc., registered in the U.S.A. and other
countries. Extensions Manager and Power Macintosh are
trademarks of Apple Computer, Inc. PowerPC is a trademark of
International Business Machines Corporation, used under
license therefrom.

10/10/96
