MCP Express is a free version of the Unisys ClearPath MCP virtual machine and system software. It includes everything necessary to run an MCP environment on standard Microsoft Windows PCs and laptops. It was first available in late 2015 and is now in its fourth release, which is based on MCP 18.0 software.

For brevity, I'll often refer to MCP Express using its Unisys style code, "XE."

This post is the first in a series that will describe how to obtain, install, and use MCP Express. If you already have XE running, the first few posts in this series may not be of much interest to you. Once we get past the basic installation tasks, we will be discussing more advanced topics in a number of areas, including networking, printing, disk management, and system configuration.

Comments and questions on this series, as on all MCP Insider blog posts, are most welcome. There are three ways you can contact us:

  1. You can post comments directly against an individual post. In order to do that, you must have signed up for an account on A UNITE Community Access account is free. Registered users who have logged on to the site will see a comment box at the end of each post.
  2. You can address "letters to the editor" to
  3. You can post messages to the comp.sys.unisys Usenet newsgroup.

Unisys intends MCP Express to be for "educational and hobbyist" use. The XE license terms prohibit its use either for production or commercial work, or for development of software for public distribution. XE restricts some MCP system features to discourage prohibited uses and to inhibit it becoming a platform for developing MCP malware. Even with those restrictions, XE still offers a very feature-rich environment for you to explore and use the MCP.

Unisys licenses the system to you on an annual basis. At present, licenses expire at the end of July each year, with a new version of the product being available to download at that time or shortly thereafter. This makes continued use of XE something of a challenge, since you must completely uninstall and reinstall the product with each release. Migrating from one release to another is a subject we will take up starting in early summer 2019 to help you prepare for the next transition.

A problem many people have getting started with XE is that you are not simply installing a Windows user application, you are setting up and will be administering a production-grade mainframe server. Some of that involves things outside the typical skill set for even those who have been long-time MCP developers. Unisys has done a fine job of packaging the product in a way that is fairly easy to install, but except for the most trivial of uses, you are going to need to become something of an MCP administrator.

If you follow the comp.sys.unisys newsgroup, you will have noticed there has been quite a bit of activity on the group involving XE and the struggles some correspondents have had with it. I have been trying to help those with problems on a one-on-one basis, but found I was dealing with the same issues again and again. Hence the impetus for this series of posts. While my goal is to discuss topics in the context of XE, a lot of the topics will also be of general interest to production MCP sites -- especially those running smaller systems such as the Libra 4xx or MCP Software Series Gold. So even if you are not that interested in XE, you may find this series of posts to have value.


The original models of what we now call MCP systems -- the Burroughs B6x00/7x00 systems of the late 1960s and early 1970s -- had hardwired instruction sets. Starting in the late 1970s, Burroughs wanted to build smaller, less expensive, entry-level systems, so they started developing micro-programmed processors. The first of these was the B5900 (ca. 1981), which can be considered to be the initial system having the "E-mode" architecture. It can also be considered to be the initial A Series system -- effectively the A0, although it was never called that.

The march towards smaller and lower-cost MCP systems continued with further development of the low-end of the A Series model range, culminating in the late 1980s with the Unisys Micro A. The processor for the Micro A was reduced to a single ISA PC board by means of several custom LSI (Large-Scale Integration) chips. Combining this board with SCSI and data communications processor cards resulted in a complete MCP system that was housed inside a standard Intel 386 desktop PC chassis. The special processor board hosted the MCP, while the 386 (running IBM OS/2) managed I/O.

At that point, further cost/performance improvement was not going to be practical using custom chips, so Unisys started pursuing emulation of the E-mode architecture on Intel Pentium chips. This approach employed the Pentium as the micro-programmed engine instead of a chip of their own design. The first of these emulated systems were the A2101 and the ClearPath NX4201 (ca. 1996), which were hosted on OEM Intel server boxes running Windows NT. As the emulation techniques improved and the Pentium chips became more powerful, the power of the emulated systems started to encroach upon that of the mid-range ClearPath NX systems. Examples of products using this approach include the ClearPath LX 5000/6000/7000 and Libra 300/400/500-series systems.

With emulation of the E-mode architecture firmly established by the late 1990s, Unisys started working on adapting the approach to run on a standard Windows PC laptop for use as a personal development system. This effort resulted in a software-only product known as the LX100, or Software Developer's Kit for ClearPath MCP (SDK). This product evolved in parallel with the MCP software releases, culminating around 2015 with the LX170 for MCP 17.0.

At that point the SDK merged with the then-new ClearPath MCP Software Series (CSS), a software-only product that customers can install on their own servers. What had been the SDK became ClearPath MCP Developer Studio Personal Edition. MCP Express is simply a somewhat restricted version of Developer Studio Personal Edition. It has the same MCP, compilers, and other system software, but with some pieces (e.g., the NEWP compiler) missing and a few features (e.g., the ability to "wrap" codefiles) disabled. See the product information sheet for the complete list of the features included in the MCP 18 version of XE.

Unisys stopped manufacturing custom processor chips and server hardware several years ago. Today, all ClearPath MCP systems use some form of emulation and are implemented using Intel Pentium processors. The high-end Libra 4000/6000/8000 systems use a different emulation technique (DBT, Dynamic Binary Translation) to achieve the necessary performance, but all current systems, including XE, run the same base of MCP system software.

What You Will Need

In order to install XE and run the MCP, you will need two things:

  1. A suitable Windows PC or laptop. See the product information sheet for minimum hardware and software requirements. This sheet is for the MCP 18.0 version of XE; the requirements may change for future versions. Note that if you are using Windows 10, it must have the Creator's Update installed. This update is included in all new Windows 10 distributions; existing Windows 10 system running Windows Update should have picked up this enhancement automatically by now.
  2. The XE download. You obtain this using a two-step process.
    • First, go to the ClearPath MCP Express page on the Unisys web site. Click the link under the "Downloads" heading. This will send you to a page where you enter information to request a download. There are also links on this page that will display the related license agreements. I strongly suggest that you read these.
    • Next, check your email. You should receive a message from Unisys within a day or two with a link that will allow you to download the install package.

The download is a zip archive about 2.6GB in size. If you have not already downloaded the install package, I suggest that you submit your request to the Unisys web site now and download the package in advance of publication of the next blog post in this series.

Before attempting to unzip the install package, right-click on its file name or icon in Windows Explorer and select Properties from the context menu. If there is an Unblock button near the bottom of the properties dialog, click that button. This will allow executable and other sensitive files to be unzipped without Windows marking them as restricted. Failing to unblock the archive may result in installation problems later.

The next blog post will pick up at this point and guide you through installation and initial configuration of MCP Express.

Additional Resources

All of the Unisys product documentation is available for free from their support site. Go to On the left side of the resulting page, under "Public Information," click the "Documentation" link. Click through the terms-of-use page, and you will arrive at a page where you can search the documentation for keywords and phrases, or browse a hierarchical table of document titles. Most of the documents of interest for MCP 18 will be under the following headings:

  • ClearPath Forward MCP Servers and Software
    • System Software
      • ClearPath MCP System Software
        • MCP Release 18.0
    • ClearPath Software Series
      • ClearPath MCP Express

Under the page accessed by the "MCP Release 18.0" heading above, there is a link to download a Documentation Zip File. This is a collection of all the software product documents for the release. The download is about 350MB, expanding to about 950MB after it is unzipped. Most of the documents are in HTML and PDF format, with a few files still in the old Windows HTML Help (CHM) format. There is an index file (index.html) you can open in your browser that provides a hierarchical table of contents, similar to the one on the support site.

I recommend that you download this documentation zip file to the PC where you will be installing MCP Express, unzip it, and start to become familiar with how to use the index. This will make most of the documentation you will need available locally, where it will be faster and more convenient to access than on the Unisys site.

Finally, Unisys has provided an email address for questions and feedback on XE: Note that XE is officially unsupported, but Unisys has been good about helping people with problems involved in downloading and getting the installer to run. If you are having problems getting things to work after the basic installation has completed, then I advise you not to use that email address to ask for help. You will do better by asking for help through the MCP Insider email address above or the comp.sys.unisys newsgroup.

Paul Kimpel

Paul started his career with Burroughs in 1970 on the then-new B6500, working with Large Systems at Burroughs and a few user sites through the 1970s. He has been an independent developer since 1979 and continues to provide consulting, training, support, and custom software development services for Unisys ClearPath MCP systems. His main interests are in the areas of data base and transaction processing system design, web-enabled user interfaces, integration of MCP and Microsoft environments, TCP/IP networking, object-oriented programming, and emulating old computer systems. He still programs in Algol.

This Post Has 3 Comments

  1. bhartweg

    I enjoyed your article and look forward to your next one on “Installation and Initial Configuration of MCP Express”.


  2. ctimmer

    Great introductory article.

    Just had one question about this quote:
    “The XE license terms prohibit its use either for production or commercial work, or for development of software for public distribution”
    Does this include developing “open source” software?


    1. Paul Kimpel

      Thanks. A copy of the license can be found in the Unisys\Installation folder you unzipped from the downloaded file as COA.html. A copy is also available at The relevant wording appears to be in the first term of the agreement:

      1. GRANT
      Upon executing this ClearPath MCP Express Non-Production Limited Software License (“MCP EXPRESS”) , UNISYS will grant you the right to obtain and use the MCP operating system and any associated documentation (“Licensed Software”) upon a single computer system (“Licensed Computer”), providing that the use of the Licensed Software does not include or support COMMERCIAL or GOVERNMENTAL purposes, activities or applications. The grant of this MCP EXPRESS License is limited to non-production evaluation, personal or educational use ONLY. This MCP EXPRESS License is void if the Licensed Software is employed for developing applications for resale or public distribution.

      I am no attorney, and what follows is certainly not legal advice, but to me the restriction centers upon the meaning of “developing applications.” I think it’s obvious that excludes distribution of object code generated by the Licensed Software. I doubt that it can be applied to source code, however, because (a) source code is not an application but a specification for an application, and (b) source code is developed by human minds and at best recorded by an instance of the Licensed Software. You cannot do anything with that source code — except admire it — without access to some (presumably licensed) MCP system where it can be turned into an application. I cannot see how it would be in the interest of Unisys to void a license because someone is willing to publicly display a workable (as opposed to working) example of how their product can be used.

      I think an enforceable exception to (b) would be source code that is generated wholly by an element of the Licensed Software, e.g., the source files generated by the SYSTEM/LOADDUMP utility for DMSII.

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Getting Started with MCP Express