spooling

[Michael Norman michael.norman@xxxxxxxx]

Herewith some useful cut-and-paste from:

PC Hardware in a Nutshell, 3rd Edition
By Robert Bruce Thompson, Barbara Fritchman Thompson
O'Reilly, July 2003, ISBN : 0-596-00513-X


23.1.2 Configuring Parallel Port Hardware
How you configure a parallel port may significantly impact performance and
overall capabilities. Even on new systems that include capable parallel
port hardware, the parallel port mode is often set to SPP by default. Many
people unintentionally cripple the performance of their parallel ports
simply because they don't know that better choices than the default are
available.
The first step to configure a parallel port for optimum performance is to
determine the capabilities of the port hardware. Examining the
documentation may help, but documentation is often cursory, misleading, or
missing entirely. Without detailed documentation, the easiest way to
determine the capabilities of the parallel port hardware is to download and
run Parallel.exe, which is available from many Internet file repository sites.
On older motherboards and expansion cards, you may have to set the mode by
using a jumper. On newer systems, you can usually set the mode using the
BIOS Setup program. The parallel port modes available are determined first
by the capabilities of the port hardware itself. Even if the hardware
supports all modes, however, the BIOS may not, so you may be limited in the
choices you can make. In general, use the following guidelines when
selecting a parallel port mode:

SPP Mode
SPP Mode, which the BIOS may also call Standard Mode, Basic Mode, 4-bit
Mode, or Unidirectional Mode, is the least-common-denominator choice, and
corresponds to the original Centronics-compatible IBM parallel port. Use
this mode only after determining that none of the more-capable modes works
with your cable or peripheral.
Bidirectional Mode
Bidirectional Mode, which the BIOS may also call 8-bit Mode or PS/2 Mode,
corresponds to the parallel modes introduced with the IBM PS/2 parallel
ports. If you choose this mode, you may also be able to choose Type 1
sub-mode (also called Non-DMA sub-mode) or Type 3 sub-mode (also called DMA
sub-mode). Choose Type 3 mode for better performance, as long as you don't
mind consuming a DMA channel. Use this mode if only it and SPP work
properly for your hardware. Also use this mode if you are using Windows NT,
which does not support EPP and ECP modes.
EPP Mode
EPP Mode, which the BIOS may instead call Enhanced Mode, is sometimes the
best choice even if later modes are available. EPP includes some control
features that are not provided by ECP, sometimes making EPP better suited
for nonprinter peripherals such as parallel port storage devices and
scanners. Also, you may need to choose EPP mode explicitly to support some
early EPP-compliant devices that do not function properly with the updated
EPP mode supported by IEEE-1284-1994 compliant ports. EPP uses IRQ channels
for flow control. It does not use DMA or provide data compression, making
it somewhat slower than the ECP mode described next.
ECP Mode
ECP Mode, which the BIOS may call Extended Mode, is usually the best choice
for transferring data to high-speed printers, although it does require a
DMA channel. Because it does not support some of the control features
provided by EPP mode, ECP mode may not be the best choice to connect
nonprinter peripherals.
IEEE 1284 Mode
IEEE-1284 Mode, which the BIOS may simply label Auto, is the most flexible
choice. If the BIOS provides this option, choose it to allow the port to
adjust automatically to the optimum mode for the device to which it is
connected.

Michael Norman