Photoshop lines: Adobe's response; more reader replies

Adobe has responded to our recent coverage (one and two) of the Photoshop inverted lines issue:

Photoshop since version 3.0 has supported performing file read and write using a higher performance mode called asynchronous input/output, or "Async I/O." This uses a feature supported by some disk and network filesystem drivers that allows overlapping disk I/O requests, thus speeding up Photoshop's file and scratch disk performance.

Async I/O is enabled with the Enable Async I/O plug-in, shipped in the Photoshop plug-ins folder. Until version 6, this plug-in was disabled by default because some disk drivers circa 1995 when Photoshop 3.0 came out that reported they supported async I/O did not do so properly, resulting in file corruption and problems. The state of disk and network file system drivers and network servers has improved greatly since then, so Photoshop 6 ships with the Enable Async I/O plug-in enabled by default.

Instances we have seen of Photoshop 6 saving corrupt files have been due to problems caused by network filesystem software when saving to network file servers of< various types. There has not been a clearly defined combination of software, drivers, server type or OS version that exhibit the problem. As reported, updating the server software, drivers or OS has fixed the problem in all cases we know of.

If users still want to disable async I/O, they need only prepend a tilde (~) to the name of the folder containing the Enable Async I/O plug-in, or to the name of the plug-in itself. For Photoshop 6.0, the plug-in is found in the Plug-Ins : Adobe Photoshop Only : Extensions folder in the Photoshop folder.

We continue to receive mail on the topic as well. Darrell Keach resolved the same problem some time ago with Photoshop 4 by disabling the Asynch I/O. Another user narrowed the cause down to a bad RAM stick corrupting files. Moreover, two users attributed the lines to the Altivec extensions, implying either the extensions or the processor itself may be at fault. Tim Nowak writes: "I found the problem to be present on several G4s. It would not happen if the Altivec extensions were not loaded. Adding the extensions would cause line artifacts when resizing an image. Our Apple service provider found nothing wrong in their tests of the processor. Humoring us, they replaced the processor. The problem went away! Apple then replaced the processor on the other problem G4, and the problem is now gone for good."

The last word While there is probably more than one cause of these lines, we have exhausted this topic, considering that hardware-related causes are extremely rare occurrences. As a result, today's coverage is the last word on this subject unless new information arises.