What is a IOUSB?

Hi, Mike-n-Go and Florin —

What's "too much" — is there a problem? Seeing repeated entries in your system.log doesn't necessarily mean there's a problem worthy of concern.

Do these messages always occur during system start-up — and are they eventually followed by something like " <small>IOUSBCompositeDevice: match category IODefaultMatchCategory exists</small>"? The entry seems to refer to a "composite class" USB peripheral acquiring appropriate drivers.
What does "IOUSBCompositeDevice ," etc. mean? The results of a Google • search for "IOUSBCompositeDevice" aren't too useful (to me, anyway) — they're mostly forum exchanges about developing USB drivers.
.kext files are "kernel extensions" — that typically boot early during the startup process (the gray screen), and provide the software interface for specific type(s) of hardware to interact with the OS. I think the typical USB drivers in OS X 10.4.x are /System/Library/Extensions/IOUSBFamily.kext and IOUSBMassStorageClass.kext. IOUSBHIDDriver.kext, IOUSBUserClient.kext, and IOUSBCompositeDevice are PlugIns to IOUSBFamily.kext. All of these provide support for USB devices.
As Florin explained, "I/O" indicates "input/output" — meaning either "the collection of interfaces that different functional units (sub-systems) of an information processing system use to communicate with each other, or the signals (information) sent through those interfaces." Apple defines the details of I/O for developers in I/O Kit Fundamentals and I/O Kit Device Driver Design Guidelines.
Your mouse, keyboard, (and joysticks) are "low-speed," human-interface USB devices (HID) supported by IOUSBHIDDriver. If any are Bluetooth devices, a separate Bluetooth driver is involved.
A USB "composite device" is a single USB device that (electronically) presents "multiple devices" to your Mac — such as a headset with HID interface, a "smartphone," a digital camera with HID interface, or a multi-function printer (-scanner-fax) — thus requiring several drivers.
In early versions of Mac OS X (and ~ the USB 1.1 specification), there were conflicts between OS X and Classic in how appropriate drivers were detected for composite devices, depending on whether the device was present at system start-up or "hot-plugged."
How can you fix it? Think about the USB devices you use that fall into this "composite device class." If you're not observing problem behavior from any of them, it's a bit difficult to be overly concerned about the log messages — depending on overall system behavior and, perhaps, succeeding log entries. Guessing, I'd wonder if perhaps device-specific driver software provided by the manufacturer isn't fully compatible with OS X 10.4.x.
If you are having a problem, you may want to check the manufacturer's website to confirm that your driver software is current — &/or whether they have recognized any conflicts between the version you're using and OS X 10.4.2, and can help you to configure a solution.
Hth,
Dean

Mike-n-Go

What type of mouse are you using? If it is a non Apple one do messages go away when you plug your apple provided one? As Dean wrote many of the (repeated) messages in system.log do not indicate that there is something wrong, worth paying attention. Of course if you are having trouble with your mac then we are talking a bout a different ball game.

My experience with usb. I have an Iomega CR-RW / DVD player combo drive. That I use only to burn cds (a tad faster on that front than the superdrive that came along with both my iMac and pb. According to System profiler it is unsupported. Although I have hundreds of such messages in system.log I never had trouble burning on this drive using iTunes or any other Apple application.

Hi again, folks —

hyphen's experience raises a good point.

Mike-n-Go, you may want to go to <small>System Profiler »» Software »» Extensions</small>, wait a moment while info is acquired, then scroll through the list and click once to select each item containing "usb" in its name — &/or the name of the manufacturer of your "composite device."

As hyphen mentioned, data should appear in the lower-right part of System Profiler's window (for each extension, one-at-a-time) that may help to determine if there's a problem. Look specifically at what's said about "Valid," "Authentic," "Dependencies," and "Integrity." From hyphen's comments, what's said may not be accurate, but it'd be good to know.

—Dean

IO = input/output
That means you have a problem with that device.