James Matheson <jmrm%cuedvax@UCL-CS.ARPA> (11/29/84)
On some machines (eg PDP11 but not VAX with 4.2) copyin and copyout use word transfers, if you try to transfer an odd number of bytes things screw up badly since the byte count (which is unsigned) goes through zero. I discovered this the hard way retrofitting some code I had written for 4.2 to PDP11 v7. You do not say what version of XENIX you have but you probably have a routine called iomove() which calls either passc/cpass or copyin/out as appropriate and so will give you speed where it can (clearly there is the overhead of an additional call and some tests).