I work in the ROM/OS group at Apple Computer and am coauthor of the SCSI Manager 4.3. I recently read Tom Thompson's review of the Mac Quadra 840AV in BYTE ("New Mac Blazes Technology Trails," January) and noticed what I believe are a few inaccuracies regarding the SCSI Manager.
File system I/O on an 840AV is slower than on previous Macs, but not because of the SCSI Manager; rather, this is due to a bug in the file system. Future revisions of the System software will fix this problem.
Second, the Mac OS does take advantage of asynchronous I/O. True, the file system is not multithreaded, which would help in disk-to-disk copies, but it is asynchronous. The big problem is that most applications don't use asynchronous I/O because hard disks aren't asynchronous. If applications writers started using the time that they get back from
the operating system to do screen updates, decompression, and so forth, they could realize a big performance win.
Clinton Bauder
Apple Computer
Cupertino, CA
I stand corrected. Thanks for pointing out that the real problem lies with a bug and not the SCSI Manager itself. It will be interesting to see if developers take advantage of the asynchronous calls.
--Tom Thompson
Flexible C++
Matthew Wilson
My approach to software engineering is far more pragmatic than it
is
theoretical--and no language better exemplifies this than C++.
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Managing the Mac SCSI System
