Emulator Version 1.01 Released

Nigel and I are pleased to announce that version 1.01 of the retro-B5500 emulator was released on 8 February 2015. All changes have been posted to the Subversion repository for our Google Code project GitHub project. The hosting site has also been updated with this release, and for those of you running your own web server, a zip file of the source can be downloaded from the GitHub repository [updated 2022-05-07].

 This is a minor release containing corrections for a few issues we have discovered in the four months since version 1.00 was released. In addition, we have changed the way the operator Control Panel is displayed and implemented a different home page for the emulator's web application.

New Control Panel

In previous versions of the emulator, you started by loading the B5500Console.html page into your browser window or tab. This page displayed the operator Control Panel from which you power on the emulator, load the MCP, and monitor the status of the running system:

Emulator Operator Control Panel

The problem with this approach was that the Control Panel occupied only a small portion at the top of the page, leaving the remainder of the page unused. In order to bring the Control Panel into view, the entire home page had to come to the top of the screen, which tended to obscure the other windows opened by the emulator, particularly the window for the SPO.

In this release, we have split the Control Panel from the home page. It now displays in its own window, which is sized just large enough to show the entire panel. This smaller window is much easier to position and use without obscuring the other windows on the screen.

That change left the B5500Console.html home page completely empty, so in order to make some use of that space, we have implemented a proper home page for the emulator site:

Emulator Site Home Page

This is the page that will now greet you when you load the emulator's B5500Console.html URL. The two blue buttons below the image on the page allow you to open the Control Panel and optionally power up the emulator.

• Clicking the Start & Power On button will open the Control Panel and power up the emulator, as if you had clicked the panel's POWER ON button. This is the option you will probably use most frequently.
• Clicking the Start - Powered Off button will simply open the Control Panel. This option is useful if you want to start by modifying the emulator configuration, which can only be done in a powered-off state.

Both buttons will be disabled when either of them is clicked, and will remain disabled until the Control Panel window is closed. Attempting to close the Control Panel while the emulator is powered on will result in the display of a warning dialog. If you choose to confirm the warning and close the panel's window, the system will be halted and the emulator implicitly powered off.

Note that in some browsers, particularly Firefox, closing the window for the new home page, minimizing it, or switching to a different tab in the same window may cause the emulator to run slowly. The reason is that Firefox tends to impose a minimum timeout delay of one second on hidden windows, whereas the emulator typically generates timeout delays in the low tens of milliseconds. The difference between the requested and imposed delays results in very slow performance.

Other Changes

The following enhancements and corrections have been implemented in this release:

1. The scroll-back buffer for the SPO and Datacom devices has been increased from 1500 to 5000 lines.
2. Switching on and off the green-bar styling for the Line Printer device did not work in Chrome due to the way the styling was being applied. This has been fixed.
3. A number of improvements have been made to the emulator's setCallback() mechanism, which is used to regulate performance and time-slice among the processors and I/O devices. These changes were imported from the Datatron 205 project, discussed below.
4. Some optimizations to the bit-field isolate/insert routines have been made. These were also imported from the Datatron 205 project.
5. A letter "B" has been added to the tape reel image used by the Magnetic Tape device. This makes the image less rotationally symmetric, and less likely to beat with the refresh rate of the screen.
6. The wiki pages have been updated for the Control Panel and home page changes in this release.

Related News

With the B5500 emulator in a stable state, I have started a new project to emulate the ElectroData/Burroughs Datatron 205 computer system. This was a vacuum-tube, drum-memory computer designed in the early 1950s. It competed against the IBM 650 and Bendix G-15. It was fairly popular in its day -- several hundred were built -- and it continued to be used into the mid/late 1960s.

The primary goal of this project is to build a web browser-based emulator that will run 205 software at its actual speed -- which is very slow by even B5500 standards. A secondary goal is to reconstruct the Algol-58 compiler written for the system by Donald Knuth in 1960 and to get that working. An assembly-language listing of the compiler survives in the papers Knuth has donated to the Computer History Museum.

Tom Sawyer of Minnesota (US) has done considerable research on the 205 and on ElectroData, which was purchased by Burroughs in 1956 and became the foundation of its commercial computer business. He has an interesting web site and a blog devoted to the 205 and its history. I contacted Tom when starting this project in the Fall of 2014; he has been enormously helpful in my work on an emulator and has shared with me a number of technical resources that are difficult to find. Tom has also written an emulator for the 205, and reconstructed a different version of the Algol-58 compiler, which he discusses in a recent blog post.

At present, my emulator is functional, but supports only paper-tape and Flexowriter (teletype) I/O. I am currently working on the Cardatron, a buffering and reformatting device that interfaced the 205 to IBM punched-card tabulating equipment. A couple of weeks ago, I posted an article on Tom's blog describing the current version of the emulator and how to use it.

As with the B5500 emulator, my 205 emulator is an open-source project hosted on Google Code. If you are interested, the emulator can be run directly from my hosting site.