In a bid to placate concerned legacy users, Wacom has explained why it has abandoned ADB and serial support for its Mac OS X graphics tablets.

Graphics professionals have used Wacom's solutions for years, and there are many legacy tablets still in use that connect via Serial or ADB connectors. USB versions are also available, says Wacom but its decision means legacy users have to buy a new graphics tablet, or remain tied to OS 9.x. Apple no longer offers serial or ADB system support, Wacom said.

Wacom professional products product manager Guido Moeller said: “Some affected products have enjoyed free technical support for eight years. USB adaptor problems are one of the biggest causes for technical support calls to us worldwide.

“An adaptor may work fine on Mac OS 9.1, but will fail to work after upgrading to Mac OS 9.2 on some Macs. Many of our customers then call Wacom for support. It's an ongoing burden for Wacom's development and tech support teams.

"Commercially available ADB-to-USB adaptors are low-speed USB devices, originally made for mice and keyboards. For them to work with a Wacom tablet on OS 9, they push the limits of USB. This works reasonably well in Mac OS 9 but Wacom is convinced OS X will not accept the excessive data rate of these adaptors."

He added: "Apple has indicated it will not resolve any OS-level issues regarding serial or ADB." Resolving such problems would break the specifications Apple implemented in order to make the operating system stable. OS X will not accept the data rate from over-clocked adaptors.

“Similar problems plague serial-to-USB adaptors on OS X, as such adaptors are optimized for using with modems. While good for modems, this cripples tablet performance.” Conceding that Keyspan offers the only serial adaptor that works "OK with tablets under OS 9", Moeller said that "this performance is unacceptable, and implementing driver support for it does not make sense",

Wacom is focusing its developmental resources on optimizing USB integration for OS X. The company has worked closely with Apple to introduce USB tablet functionality to OS X, but "Apple is not prioritizing any efforts towards legacy support," Moeller said. This reflects Apple's strategy to convince its customers to migrate to OS X."

“We do hope that discussing the reasons for the decision may make it easier for customers to understand and accept the decision,” Moeller said.