The firmware update page is kind of hard to find, so...

For all Yam drives click here

For F1 specific click here

Most F1's shipped with 1.0c firmware, latest is 1.0f

Change log:

What's New in 1.0f (updated: December 27-02):

Allowed CRW-F1 to switch the maximum rotation speed in reading Audio CD between 8700rpm and 4700rpm.
For more details, click here.
Added support for following CD-R discs for 44x writing.
CMC (48x), Imation (48x), MPO (48x, 52x), Plasmon (52x), Sky Media (52x), Sony (48x)
Added support for CMC Ultra Speed CD-RW disc (24x).

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What's New in 1.0d (updated: October 4-02):

Added 24x and 32x writing.
*"Optimum Writespeed Control" option needs to be disabled.
Improved 16x and 24x writing quality of Ultra Speed CD-RW discs.

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What's New in 1.0c (updated: August 27-02):

Added support for following CD-R discs for 44x writing.
Maxell (32x), NANYA (48x), Daxon (40x), Prodisc (48x)
Improved writing quality of CD-R discs by refined running optimum power control.
Fixed problem with DiscT@2 where error message comes up if you try to burn images/graphics to the outer edge of a disc.
Fixed problem where the drive icon of CRW-F1 disappears if you load/eject a CD repeatedly.

xen-uno

This firmware update takes care of problem with Nero 5.5.10.15a in regards to max write speed***

***except on Verbatim DataLifePlus CD-RW's...still maxes out at 4x

After updating the F1 with the latest firmware, the drive is listed only as UDMA-0 (used to be UDMA-2) in Win XP. No complaints on its performance, it burns a 667MB CD in 3:05, but I am still curious.

Did anyone else observe this?

By the way: To get UDMA-2 back, simply delete the channel (primary or secondary) on which your CD drive is in the device manager and reboot. Upon detecting the 'new' device, Win XP will correctly assign the highest possible UDMA mode.

Edit: How to fix it added