- Note that the isa driver should not be removed.

- Note that the SCSI subsystem should not be removed when umass(4) is
  enabled.

Prompted by:	Yet another kernel compile problem on #bsd-dk @ EFnet

en_US.ISO8859-1/books/handbook/kernelconfig/chapter.sgml

@@ -925,7 +925,8 @@ options 	_KPOSIX_PRIORITY_SCHEDULING</programlisting>
 
     <programlisting>device          isa</programlisting>
 
-    <para>All PCs supported by &os; have one of these.  If you have an
+    <para>All PCs supported by &os; have one of these.  Do not remove,
+      even if you have no ISA slots.  If you have an
       IBM PS/2 (Micro Channel Architecture), &os; provides some
       limited support at this time.  For more information about the
       MCA support, see
@@ -1027,6 +1028,13 @@ access)</programlisting>
     <para>SCSI peripherals.  Again, comment out any you do not have, or if
       you have only IDE hardware, you can remove them completely.</para>
 
+    <note>
+      <para>The USB &man.umass.4; driver (and a few other drivers) use
+	the SCSI subsystem even though they are not real SCSI devices.
+	Therefore make sure not to remove SCSI support, if any such
+	drivers are included in the kernel configuration.</para>
+    </note>
+
     <programlisting># RAID controllers
 device          ida        # Compaq Smart RAID
 device          amr        # AMI MegaRAID