Sony PCG-SRX99 VAIO User Guide (primary manual) User Manual page 64

To connect a USB mouse
Plug the mouse cable into the USB port. PCGA-UMS1 series drivers have already been installed.
Connecting a USB Mouse
A serial mouse or PS/2 mouse is not compatible with this VAIO computer.
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See the manual supplied with your mouse for more information on its installation and use.
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