Getting Your Legacy DOS Programs to Print on Modern Systems via LPT Printer Port

Many businesses still rely on legacy DOS programs for critical operations. While these programs can often be made to run on modern Windows systems, printing can present a unique set of challenges, especially when dealing with Lpt Printer Ports. This article will guide you through the process of enabling printing from your DOS applications on contemporary hardware, focusing on utilizing the often-required lpt printer port.

Understanding the LPT Printer Port in Modern Context

The lpt printer port, also known as a parallel port, was the standard interface for connecting printers to computers for many years. DOS programs, particularly older ones, are often configured to print directly to a specific lpt printer port, most commonly LPT1. However, modern computers rarely include physical parallel ports. They have been largely replaced by USB and network connections. This shift creates a hurdle when trying to print from DOS applications that are hardcoded to use lpt printer ports.

The Challenge: DOS Printing to LPT Ports on New Machines

The core problem arises from the incompatibility between legacy DOS printing expectations and modern hardware configurations. DOS programs are designed to communicate directly with hardware ports like LPT1. Modern operating systems and hardware, however, often abstract these direct hardware interactions for better compatibility and management. When you attempt to print from a DOS program expecting an lpt printer port on a new machine, you might encounter:

• Lack of Physical LPT Port: Most modern computers, especially laptops and newer desktops, do not have a physical DB-25 parallel port.
• Operating System Incompatibility: Even if a physical port is present (perhaps on older hardware), modern Windows versions may not fully support direct hardware access in the way DOS programs expect.
• Driver Issues: Modern printers are designed with USB or network interfaces in mind, and their drivers are not always compatible with direct lpt printer port communication as envisioned by DOS applications.

Solutions for LPT Printer Port Printing from DOS

Despite these challenges, there are effective methods to bridge the gap and enable printing from your DOS programs, even when they insist on using an lpt printer port. Here’s a breakdown of a proven approach:

1. Utilizing USB to Parallel Adapters

The first step in many cases is to physically connect your parallel printer to a modern computer. This is commonly achieved using a USB to DB25 parallel printer adapter.

• Adapter Installation: These adapters are generally plug-and-play. When connected, Windows should automatically recognize and install the necessary drivers. Critically, these adapters are not typically recognized as traditional lpt printer ports by the system.

• Virtual USB Ports: Instead of creating an lpt printer port, the adapter is usually recognized as a USB device, and the printer is associated with a virtual USB port like USB001 or USB002. You can verify this in “Devices and Printers” after installation.

2. Installing the Printer Driver

Once the physical connection is established, you need to install the correct printer driver on your Windows system.

• Adding a Local Printer: Go to “Devices and Printers” and select “Add printer.” Choose “The printer that I want isn’t listed” and then “Add a local printer or network printer with manual settings.”

• Using an Existing Port: In the port selection dialogue, crucially select “Use an existing port” and choose a virtual USB port (e.g., USB001) from the dropdown list. Do not select any LPT port options at this stage, as the adapter is not functioning as a native lpt printer port.

• Driver Selection: You’ll be prompted to select the printer manufacturer and model. If your exact printer is not listed (common with older printers), you may need to find a compatible driver. In the original article’s example, a Panasonic dot matrix printer was successfully configured using an Epson FX Series driver included with Windows. Manufacturer support websites or online forums can be valuable resources for finding compatible drivers for legacy printers.

3. Redirecting LPT1 Port via Printer Sharing and net use Command

With the printer installed and working on a virtual USB port, the final step is to redirect the DOS program’s expected lpt printer port (LPT1) to this USB-connected printer. This is done using printer sharing and the net use command in Windows.

• Printer Sharing:

  1. Right-click on the installed printer in “Devices and Printers” and select “Printer properties.”
  2. Go to the “Sharing” tab.
  3. Check “Share this printer.”
  4. Give the printer a short and simple share name (e.g., “DOSPRINT”). Unchecking “Render print jobs on client computers” can sometimes improve compatibility with older applications.
  5. Navigate to the “Security” tab and ensure that the user account running the DOS program has the necessary permissions to print. Initially, ensure the user has at least “Print” permissions. Domain administrator rights, as mentioned in the original article, are generally not necessary and should be avoided for security best practices unless absolutely required after troubleshooting permissions.

• net use Command in Batch File: The redirection is implemented using the net use command. This command can be incorporated directly into the batch file (.cmd) that launches your DOS program, making the printing solution automatic.

   @echo off
   :: Delete any existing LPT1 mapping (to avoid conflicts)
   net use lpt1 /delete /y
   :: Map LPT1 to the shared printer
   net use lpt1 \%COMPUTERNAME%DOSPRINT /persistent:yes
   :: Start the DOS program
   :: ... (command to launch your DOS program)

  • net use lpt1 /delete /y: This line first removes any existing mapping for LPT1. The /y switch suppresses the confirmation prompt. This is important to ensure a clean redirection each time the batch file runs, especially if previous mappings might exist.
  • net use lpt1 \%COMPUTERNAME%DOSPRINT /persistent:yes: This is the core command. It maps the lpt printer port LPT1 to the shared printer.
    • lpt1: Specifies the local port to map.
    • \%COMPUTERNAME%DOSPRINT: Specifies the network path to the shared printer.
      • \%COMPUTERNAME%: %COMPUTERNAME% is an environment variable that automatically resolves to the local computer’s name. Alternatively, you could use the computer’s network name or IP address if accessing a shared printer on a different machine.
      • DOSPRINT: This is the share name you assigned to the printer in the sharing settings. Ensure this name exactly matches the share name you configured.
    • /persistent:yes: This makes the printer connection persistent, meaning it will be restored automatically after a reboot. This is generally desirable for consistent DOS application printing.

Troubleshooting Common Errors

• System Error 5 (Access Denied): This often indicates a permissions issue.

  • Security Tab: Double-check the “Security” tab of the shared printer properties. Ensure the user account running the DOS program (or a relevant group they belong to) has “Print” permissions. “Everyone” group can be used for initial testing but should be replaced with more specific permissions in a production environment.
  • Domain vs. Local Accounts: If your computers are part of a domain, ensure that the user account context is correctly resolved. For simpler setups, ensure both the computer sharing the printer and the computer running the DOS program are on the same network and can resolve each other’s names.

• System Error 66 (The network resource type is not correct): This usually points to syntax errors in the net use command.

  • Syntax Check: Carefully review the command syntax, especially the computer name and printer share name. Misspellings are common causes.
  • Double Backslashes: Ensure you have double backslashes \ at the beginning of the network path.
  • Share Name Accuracy: Verify that the printer share name in the net use command exactly matches the share name configured in the printer properties.

Conclusion: Bridging Legacy and Modern Printing

Printing from DOS programs to lpt printer ports on modern systems requires a layered approach. By using USB-to-parallel adapters, installing appropriate drivers for virtual USB ports, and employing printer sharing with the net use command, you can effectively redirect DOS printing output to modern printers. This method provides a practical solution for businesses that still rely on legacy DOS applications but need to integrate them with contemporary printing infrastructure. Remember to carefully check printer sharing permissions and net use command syntax for smooth and reliable DOS printing.

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References:

• net use command documentation: https://technet.microsoft.com/en-us/library/bb490717.aspx