

                 READ PROBLEMS ON HALF HEIGHT DRIVES
                    WHILE USING P SYSTEM  PASCAL


If you have had troubles with programs written on the UCSD p system 
working on half height drives, such as TEAC 55B drives which are 
commonly added to the IBM PC, you may be able to modify your drives 
to solve the problem.

We had problems transferring files with Advanced DB Master, which 
is written in P system pascal.  It is logical to assume that other 
programs written on the P System, would exhibit similar symptoms.  
We would pick up a lot of read errors, and sometimes the computer 
would simply not recognize that there was a disk in the system.  At 
first look, it appeared that the problem was the disk drive, but we 
even replaced the drive with a brand new one, with no luck.

One of the first things that the P system does when it accesses a 
drive is to read the volume name that is located on each formatted 
P system disk.  If it does not read this volume name, the system 
will assume that there is no drive in the computer, and simply will 
not access any files connected with that drive.

Many half height drives are built with a solenoid that drops the 
head onto the disk when the computer needs to access the drive.  
Most full height drives leave the head resting on the disk whenever 
the door is closed. 

The operating system sometimes will not allow enough time for the 
head to drop onto the disk and read the volume label.  Therefore, 
it can erroneously lock that disk drive out of the system.

The solution on the TEAC drive is to adjust an allen screw that 
controls the height of the head while the solenoid is in the open 
position.  Turning this screw about two turns counter clockwise 
will allow the head to ride on the drive at all times.  This  
cleared up our read problems with Advanced DB Master entirely.  I 
can see no reason that this would be any more damaging to a disk 
than the regular full height disk drives are.

Most other types of half height drives would probably have a 
similar adjustment that could be made to bypass the head load 
solenoid.

Perhaps one of you programmer types out there would be able to come 
up with a software patch to the operating system, to allow a little 
more time before it reads the volume label.  If so, please write or 
call me and let me know.

Frank Sousa
MTSI
Building 102 Spokane Industrial Park
Spokane, Washington 99216
(509) 926 6705
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