Configuring the retro-1620 Emulator

This page describes how to configure the system and peripheral devices for the emulator.

The Configuration Window

The emulator home page has a button below the picture of the 1620 system labeled Configure System.

Clicking that button opens a sub-window that shows the current system configuration and allows you to change it. The button is enabled -- and the configuration can be accessed -- only when the emulator is in a powered-down state. This is the state immediately after loading the home page into your browser or after double-clicking the POWER switch on the Control Panel to shut down the emulator.

The configuration sub-window is rather large, and will scroll on most displays. It looks similar to the following:

This window has areas for selection of global system properties and input/output peripheral devices. You can change the configuration by altering the controls in this window and clicking the SAVE button. If you only want to view the configuration or discard any changes you have made, click CANCEL. Both buttons close the window.

The DEFAULTS button will discard the current configuration and replace it with the default one described in the next section.

Persisting the Configuration

The configuration data for the emulator is saved using an HTML5 feature known as Local Storage, implemented in Javascript by the window.localStorage object. Local Storage is supported by reasonably recent versions of all the major browsers. It allows a web page to store information that will persist across browser sessions and workstation restarts. For example, Firefox stores this data in a SQLite data base on your local disk drive.

Data in Local Storage is subject to the browser's same-origin policy, meaning that separate copies of the data are maintained for each combination in the URL scheme (http/https), host name, and port number. Thus, if you are accessing the emulator on two different web sites, you will have a different copy of the configuration data for each one.

The host name is taken literally. For example, you can access the emulator on the hosting site either at https://www.phkimpel.us/IBM-1620/ or at https://phkimpel.us/IBM-1620/. Both URLs will access the same physical files on the server, but those are different origins as far as the browser is concerned. In addition, Local Storage data is maintained differently by different browsers, so if you use the emulator with, say, both Firefox and Google Chrome, each browser will have separate Local Storage data.

When you first run the emulator in your browser, the emulator will recognize that no configuration data is present, and will automatically create a default configuration for you. This is the same configuration established by the DEFAULTS button on the configuration page:

• 40,000 digits of memory
• No index register, floating point arithmetic, binary capabilities, or persistent window positions.
• IBM 731 Selectric typewriter
• IBM 1622 card reader/punch
• No line printer, disk devices, or other I/O devices.

The following sections discuss the areas of the System Configuration window and how you use them to specify the set of peripherals to be included in your 1620 system.

System Properties

This section discusses the emulator's global system properties.

Memory Size -- Using this pull-down list, you can select the amount of memory the emulator will use: 20,000, 40,000 or 60,000 digits. Attempting to access memory locations beyond the size set in the configuration will result in the emulator halting with a MAR check stop.

Index Registers -- Ticking this check box will enable index register functionality and the instructions BLX, BLXM, BSX, BX, BXM, BCX, BCXM, and MA. When the box is unticked, these instructions are invalid and will cause a MAR check stop. In addition, flags over the middle three digits of instruction P and Q addresses will be ignored during the I-cycles of instruction fetch.

Floating Point -- Ticking this check box will enable floating point arithmetic functionality and the instructions FADD, FSUB, FMUL, FDIV, FSR, and FSL. When the box is unticked, these instructions are invalid and will cause a MAR check stop.

Binary Capabilities -- Ticking this check box will enable the binary instructions BBT, BMK, ORF, ANDF, EORF, CPLF, OTD, and DTO. When the box is unticked, these instructions are invalid and will cause a MAR check stop.

Persistent Window Positions -- By default, the emulator will size and position its windows at locations on your primary (or only) workstation display as determined by the size of the display. Ticking this check box causes the emulator to remember each window's position and reinstate the windows in those positions the next time the emulator is initialized.

Use Multi-Screen Positioning -- This option is enabled only when the Persistent Window Positions check box is ticked. It is effective only when your local workstation has multiple displays and your browser supports the Window Management API. As of this writing, the standard for the API is in draft status and only Google Chrome supports it. As a result, the emulator's handling of multiple monitors is both browser-dependent and somewhat complex. See "Multiple Display Window Positioning" below for details.

Input/Output Devices

This section discusses configuration of the emulator's input/output devices.

731 Typewriter

The console typewriter is part of the standard 1620 system configuration; most 1620 software will not work properly without it. The System Configuration window displays the settings for the typewriter's margins, number of columns, and tab stops, but these are set on the typewriter's window after the emulator initializes. By default, these settings are:

• Margin-Left 0
• Margin-Right 80 (i.e., an 80-column width, max is 85)
• Tabs at columns 9, 17, 25, 33, 41, 49, 57, 65, 73, and 81.

For details, see Using the Typewriter.

1622 Card Reader/Punch

The 1620 card reader and card punch devices were packaged together in one cabinet. Internally, they are all but completely mechanically and electrically separate, but are included or excluded in the configuration as one. There are two options that can be selected on the System Configuration window.

Reader/Punch Speed:

• None excludes both units from the configuration.
• Model 1: 250/125 CPM selects 1622 Model 1 speeds -- 250 cards/minute read, 125 cards/minute punch.
• Model 2: 500/250 CPM selects 1622 Model 2 speeds -- 500 cards/minute read, 250 cards/minute punch.

Punch Stacker Capacity determines the number of cards that can occupy the punch's output stacker before a stacker-full condition occurs and the punch is made not ready. The value of this field can range from 100 to 999,999. For details, see Using the Card Punch.

1443 Printer

The 1620 line printer has these settings:

Printer Speed:

• None excludes the unit from the configuration.
• Model 1: 150 LPM selects 1443 Model 1 speed with a 52-character type bar -- 150 lines/minute.
• Model 2: 240 LPM selects 1443 Model 2 speed with a 52-character type bar -- 240 lines/minute.

Columns selects the number of print columns, 120 or 144. Note that the version of the Monitor I operating system available from the Computer History Museum supports only 120 columns.

The window displays the current carriage control tape configuration, but this is set on the printer's window after the emulator initializes. It defaults to a carriage tape of infinite length (i.e., no channel 9 or 12 punches to designate end-of-page) and all channel skips acting as a skip to top-of-form. For details on preparing and loading a carriage control tape, see Using the Line Printer.

1627 Plotter

The 1620 plotter has these settings:

• None excludes the unit from the configuration.
• Model 1: 11-inch carriage includes the unit in the configuration.

The plotter has an option to scale the plot. The default 50% setting draws two plotter steps per screen pixel. The 100% setting draws one plotter step per pixel, but this causes the plotter window to be almost twice as wide on the screen as compared to the 50% setting, unless the Persistent Window Positions option described above is selected, in which case the window's retained size will be used. See the Using the Plotter wiki page for more information on plot orientation and scaling.

1311 Disk

The 1620 disk subsystem supports up to four disk modules. Module 0 must exist in order for any other modules to be recognized. Any combination of modules in addition to Module 0 may be configured. Each module has three check boxes to control its behavior:

• Exists -- if this box is ticked, the module is included in the system configuration. If this box is unticked, none of other check boxes for that module are relevant.
• Started -- If this box is ticked, the module is powered on. It corresponds to the START/STOP button on the disk control panel.
• Enabled -- If this box is ticked, the module is enabled for reading and writing. It corresponds to the ENABLE switch on the disk control panel.

All three check boxes must be ticked in order for the module to be usable by the system. Changes to the Started and Enabled check boxes are reflected in the settings on the disk control panel and vice versa. The states of all three check boxes are preserved across emulator restarts.

The Image setting on the window shows the name of the disk pack image file last loaded to the module. If the module was initialized via the disk control panel, this will read (initialized).

For details, see Using the Disk Drive. Note that enabling index registers can cause problems in the Monitor I operating system due to the way that Monitor I was not careful about allowing flags in address digits. You may wish to disable index registers when using Monitor I.

Multiple Display Window Positioning

By default, the emulator will automatically determine the size and position of the Control Panel and I/O device windows on your workstation display. If you resize or move the windows, these changes will not be preserved across an emulator restart, and the windows will be placed at their automatic positions the next time the emulator is initialized.

Two check boxes discussed above under "System Properties" control the persistence of window sizes and their positioning:

• Persistent Window Positions
• Use Multi-Screen Positioning

If both check boxes are unticked, the emulator uses its default automatic window sizing and positioning method.

If the Persistent Window Positions check box is ticked, the emulator will remember the size and location of each window across an emulator restart, but the way this works depends on whether your workstation has multiple display devices and whether your browser supports the Window Management API. The Use Multi-Screen Positioning check box is relevant only if (a) Persistent Window Positions is ticked, (b) your workstation has multiple display devices, and (c) your browser supports that API.

As of this writing, only Google Chrome supports that API, the specification for which is still in draft status. Therefore, the following information and the emulator's behavior may change unexpectedly as standardization of the API proceeds. For now, the behavior can be described in two parts, one for Chrome and one for all other browsers.

The emulator maintains window position and size information for each of its windows under three "modes":

• Auto -- this is the default, and is used when Persistent Window Positions is not ticked. Windows will be positioned and sized by the emulator. Any changes to window size or position will not be preserved across emulator restarts.

• Single -- this is enabled when Persistent Window Positions is ticked in the configuration and Use Multi-Screen Positioning is not. This causes the current window positions to be preserved when the emulator is powered off and then reinstated the next time the emulator initializes, but the way this works currently differs between Chrome and the other browsers, as discussed below.

• Multiple -- enabled when Persistent Window Positions and Use Multi-Screen Positioning are ticked in the configuration, your workstation has multiple display devices, and the browser supports the Window Management API. This is intended to support multi-monitor configurations.

The emulator persists window size and position information across emulator restarts separately for Single and Multiple modes, but not Auto mode. This allows you to maintain different window configurations for single- and multiple-display workstation configurations, e.g., a laptop that you use at your desk with one or more additional displays, but also standalone with only the laptop's screen.

If neither check box is ticked, the browser will use "Auto" mode positioning. Windows will be positioned automatically. If you have multiple monitors, the windows should be placed on the same display as the main window.

Ticking Persistent Window Positions will enable "Single" mode positioning. The sizes and positions of the windows will be saved when the emulator is powered off, and the emulator will attempt to restore the windows to those positions the next time it is started.

• Under Chrome, when the Multi-Screen box is not ticked, the windows will all be placed on a single display, regardless of how many displays are present. You can move windows to other displays, but they won't be restored there.

• Other browsers, however, will consider the multiple displays to be one contiguous space. Thus, you can move the windows to other displays, and those browsers will attempt to restore those windows to their former positions in the contiguous display space. If you later remove a display and restart the emulator, the browser will constrain the window positions to the newly available display space.

Ticking Use Multi-Screen Positioning will attempt to use "Multiple" mode positioning by means of the Window Management API. At present, this is the only way for Chrome to be able to restore windows to multiple displays. This setting will only be effective if (a) the Persistent Window Positions check box is ticked, (b) the browser supports the API, and (c) the workstation currently has multiple displays. If all those conditions aren't met, the emulator ignores the Multi-Screen check box and reverts to either "Auto" or "Single" mode positioning, depending on the setting of the Persistent check box. At present, the Multi-Screen check box will be ignored for any browser other than Chrome.

By default, Chrome is supposed to prompt for permission to use the Window Management API when you first try to use the API, but for some reason the prompt never appears. Instead, Chrome throws an exception. Since this is quite a new API, it's probably a bug.

Fortunately, there's another way to get the permission granted:

1. Open Chrome's settings panel from the 3-dot icon on the right of the address bar (or you can enter about:settings in the address bar and press Enter).
2. From the "Settings" menu on the resulting page, select "Privacy and Security."
3. On the next view, select "Site settings."
4. On the next view, expand "View permissions and data stored across sites."
5. Select "www.phkimpel.us" or "phkimpel.us" (or whatever site you're running the emulator from). There's a search box in the upper-right corner if the list shows a lot of sites.
6. On the next view, scroll the list of permissions to "Window management." On the right of that is the current permission (probably set to "Ask").
7. Change the permission to "Allow." The change takes effect immediately.

You could also try this method, which may be quicker:

1. Open the Developer Tools (F12 or via "More tools" on the 3-dot menu).
2. Click the "Console" tab.
3. At the command prompt, enter await window.getScreenDetails() and press Enter. A prompt should appear over the main window (make sure it's not covered by the Developer Tools window). Click the "Allow" button.
4. Close Developer Tools.

This window positioning scheme is a little complex, but is designed this way in an attempt to have sensible behavior when the workstation's display configuration changes. It also gives you the ability to opt out of using the Window Management API and having to worry about its permissions. You only need to give permission for the Window Management API once per origin from which you load the emulator, but some users may want to run in Single mode even if they're running Chrome and have multiple displays.