string

zs0 - tty serial port 0 (/dev/ttya)
zs1 - tty serial port 1 (/dev/ttyb)
zs2 - keyboard port (/dev/kbd)
zs3 - mouse port (/dev/mouse)
Action
Silo overflows indicate that data in the respective serial port FIFO has been lost.
However, consequences of silo overflows might be negligible if the overflows occur
infrequently, if data loss is not catastrophic, or if data can be recovered or reproduced.
For example, although a silo overflow on the mouse driver (zs3) indicates that the
system could not process mouse events quickly enough, the user can perform mouse
motions again. Similarly, lost data from a silo overflow on a serial port with a
modem connection transferring data using uucp(1C) is recovered when uucp(1C)
discovers the loss of data and requests retransmission of the corrupted packet.
Frequent silo overflow messages can indicate a zs(7D) hardware FIFO problem, a
serial driver software problem, or abnormal data or system activity. For example, the
system ignores interrupts during system panics, so mouse and keyboard activity
result in silo overflows.
If the serial ports experiencing silo overflows are not being used, a silo overflow
could indicate the onset of a hardware problem.
Technical Notes
Another type of silo overflow is one that occurs during reboot when an HDLC line is
connected to any of the terminal ports. For example, an X.25 network could be
sending frames before the kernel has been told to expect them. Such overflow
messages can be ignored.
Alphabetical Message Listing 213