I/O Buffering Feature Introduction and Usage with Data Spooling

I/O buffering is a feature that was first available in the HP LaserJet 4/4M Plus family printer. This feature allows a quicker "back to user" time by streamlining the data throughput.

While the actual print speed is reduced by using any type of spooling, I/O buffering is a way for the printer to accept more data from the active data stream than it can process at a given moment. Buffering is also a way to accept data from non-active data channels.

Benefits

The primary way that I/O buffering is employed is to spool data from the host computer. When spooling data from the host computer there is a buffer of memory allocated to store data sent from the host to the printer. This buffer is an area of memory that revolves so that the host can send data to the printer before the printer is ready to process it. The host computer can then continue on to other tasks.

Another way that I/O buffering helps is by accepting data from non-active ports. This means that if one connection to the printer is active, the printer can buffer or store data from another connection. An example of this would be if the MIO port were active and currently printing a job from a Novell print queue, a small amount of data could be spooled from the parallel port. The amount of data that can be spooled to an inactive port varies depending on how much memory is allocated to the entire I/O buffering pool and how much is already allocated to other ports.

Determining memory allocation

The maximum amount of memory available is determined by:

Total memory in the printer

Current printer resolution

Amount of memory allocated to Resource Saving

Amount of free memory needed to print on the largest paper size that the printer supports

If the I/O option is turned to Auto, the printer automatically calculates an appropriate amount of memory to dedicate to I/O buffering based upon the amount of memory in the printer and the amount required to print a page on the largest paper size that the printer supports. The final amount of memory that the printer has allocated in the Auto mode can be verified by printing a self-test page for the printer.

Once memory has been allocated to I/O buffering by using either the On or Auto options, it is unavailable for any other processes, including page descriptions and resource saving. A small increase in performance may be noticed by allowing the printer to use the Auto configuration. Allocating more memory will probably not result in large increases in performance for most applications.

* Optional printer memory (over the printer's 2 MB of base memory) can be fully allocated to I/O buffering. Therefore, each megabyte of optional printer memory (over 2 MB) contributes an additional 100 KB to Auto I/O buffering and an additional 1 MB of maximum allowable I/O buffering.

NOTE: Duplexing will not affect I/O buffering memory requirements. However, duplexing increases memory requirements so if you experience 20 MEM OVERFLOW problems, add optional memory or reduce I/O buffering or resource saving.

* Optional printer memory (over the printer's 6 MB of base memory) can be fully allocated to I/O buffering. Therefore, each megabyte of optional printer memory (over 6 MB) contributes an additional 100 KB to Auto I/O buffering and an additional 1 MB of maximum allowable I/O buffering.

Duplex

* Optional printer memory (over the printer's 12 MB of base memory) can be fully allocated to I/O buffering. Therefore, each megabyte of optional printer memory (over 12 MB) contributes an additional 100 KB to Auto I/O buffering and an additional 1 MB of maximum allowable I/O buffering.

Using I/O buffering

I/O buffering is implemented by reserving printer RAM to buffer information from the I/O ports.

Enabling I/O buffering on the HP LaserJet 4 and LaserJet 4V family printers

NOTE: A 09 MENU RESET will not return the I/O buffering setting to the factory default.

To enable I/O buffering on the HP LaserJet 4 and HP LaserJet 4V family printers, perform the following steps:

Turn the front panel option I/O Buffer to either On or Auto.

If the I/O option is turned to On, the user can allocate the amount of memory to dedicate to I/O buffering by changing the value of I/O Size.

NOTE: To achieve a good balance between memory used for the I/O buffer and performance, use the Auto setting.

Enabling I/O buffering on the HP LaserJet 5 family printer

To enable I/O buffering on the HP LaserJet 5 family printer, perform the following steps:

Press the MENU key until MEMORY CONFIGURATION MENU appears in the printer display.

Press the ITEM key until I/O BUFFER=ON appears in the printer display.

NOTE: "I/O BUFFER=" could show On, Off, or Auto.

Press ITEM to change the selection.

Press SELECT to set the new selection as default.

Enabling I/O buffering on the HP LaserJet 4000 family printer and newer

To enable I/O buffering on the HP LaserJet 4000 family printer, perform the following steps:

Press the MENU key until I/O MENU appears in the printer display.

Press the ITEM key until I/O BUFFER=ON appears in the printer display.

NOTE: "I/O BUFFER=" could show On, Off, or Auto.

Press ITEM to change the selection.

Press SELECT to set the new selection as default.

I/O buffering with multiple I/O ports

There is one Direct Memory Access (DMA) channel for the serial and parallel ports, and the parallel port has priority for I/O buffering.

Prior to the implementation of I/O buffering, if several jobs for one protocol were found that needed processing, the printer would service all jobs for that protocol before checking the other protocols.

With the combo cards, the printer will now service one job per each protocol on a rotating basis until all jobs are printed. The exception to this is the AppleTalk protocols. The way the Apple protocol works, the printer will service all jobs on this protocol until they are printed, then move on to the next protocol.

NOTE: The AppleTalk protocols (LocalTalk and EtherTalk) cannot be buffered efficiently due to their two way communications, so with these protocols I/O buffering is explicitly disabled.

I/O buffering on the MIO can occur while either the serial or the parallel port is busy. The status of the ports when data is being received is illustrated by the following table:

When the printer detects a job boundary (for instance, a PJL sequence, a delay (timeout), or a Ctrl D in a PostScript job), it moves to the next port using the following order. (The order in which the job was received is not considered.)

Parallel

Serial

MIO

AppleTalk

NOTE: AppleTalk is always considered busy when it is not the active port, because the Macintosh expects an answer from the printer within a specific time limit.

Setting up Windows to use I/O buffering

If Print Manager is on, it will intercept print jobs and no I/O buffering will occur. I/O buffering offers no benefit in a single-user environment, unless you are using a PC that has a fast (200 KB) parallel port. If printing in a single-user environment and are not using a PC with a fast parallel port, Print Manager works better than I/O buffering and does not consume printer memory. You will only benefit from using I/O buffering in Windows applications if you are printing in a multi-user environment.

To use I/O buffering in Windows, turn off Print Manager by clearing the Print Manager Enabled checkbox in the printer Control Panel.