Tracy asks:

> We recently switched our line printer from HPIB to serial at 19,200bps.
>  When printing spooled output, any IO rate difference goes unnoticed, but
for
>  "hot" jobs, the actual printing rate is about half as fast as it used to be
>  using HPIB.
>
>  Is/was HPIB really twice as fast as 19.2?
>
>  Could be our HPIB profile included stripping trailing spaces and the serial
>  profile does not or some such difference, but...

HP-IB is significantly/substantially/enormously faster than 19.2 Kbps, but
because your target device is a printer, you wouldn't ordinarily see that
difference. The printer just lops along at its own pace. It couldn't go any
faster if you had a T1 line into the device.

However, 19.2Kbps should also be much faster than the printer, thus you
shouldn't see any difference at all between the two forms of connection if
you're just watching the paper move through the printer. Both transport
mechanisms should keep the printer's buffer completely full at all times
while a spoolfile is being directed to the printer.

If you're seeing a difference between the two print speeds, it can only be
due to one of several conditions:

     o The first is that are great gaps of time during which the host is
simply not delivering output to the printer because it is intensely busy
doing something else, or

     o More likely, the host is waiting for some sort of flow control
(XON/XOFF) feedback, letting the host know that the printer's buffer is low
enough such that it can accept new input. If the printer has these large gaps
of time when it's waiting and not printing, but the host does resume
spoolfile downloads episodically later, it's quite likely that the proper
flow control protocol hasn't been properly established in the printer -- and
the host printer driver is simply timing out and delivering the next little
bit of output.

The least likely condition is that the printer driver is filling the output
spoolfile with massive number of nulls or trailing spaces, but even if it
were, it should still not slow printing all that much. Both HP-IB or 19.2K
serial should be more than fast enough to keep the printer's buffer full at
all times. Further, most printers are smart enough to computionally "eat" all
of those additional nulls and spaces before they are delievered to the print
head.

Wirt Atmar