---

Table of Contents

1. Quick Start
2. The Front Panel (Panel page)
3. The Operator Console
4. User Terminals (TTY 1 / TTY 2)
5. The LP11 Line Printer (Printer page)
6. The VT11 Vector Display (Display page)
7. Storage (paper tape, disk & tape images)
8. Machine State (STATE button)
9. Configuration (Config page)
10. Guest Operating Systems
11. Buttons, Shortcuts & Indicators
12. Troubleshooting
13. The Desktop App

---

Quick Start

On your very first launch the emulator greets you with a short onboarding hint that explains what to do right away — which page to open, the mounted guest OSes and their boot commands. A Quick boot button next to Got it opens the wizard directly, so a first-time user can see a guest OS running in one click:

The magic wand

In a hurry? Use the magic wand button in the top-right corner of the window. It stays on every page except Info. One click does everything:

1. Opens a picker listing every guest operating system (and the paper tapes) whose image this build ships — the picker is filtered by the build manifest (media/manifest.json), plus any images you have imported by drag & drop. Paper tapes always stay listed.
2. Chooses one, switches to the operator console, and reboots the machine.
3. Types the boot command — and the login too, where the credentials are known (e.g. Unix V5: boot rk0 → unix → login root).

The wizard is prompt-aware: it watches the console output and types the login only when the guest actually prints login:, so slow boots with lots of output (e.g. 2.11 BSD) still reach the prompt reliably. Each guest also declares the machine profile it wants — e.g. RT-11/RSX/RSTS enable the LP11 line printer, and Unix V5/BSD force a teletype console — so the wizard reconfigures the machine if needed and resumes the boot automatically. Every wizard boot starts on a fresh page (clean paper and clear screens).

While the sequence is being typed, a toast says "Autoloading in progress…" and locks the emulator's input: the terminals, the front panel and the page itself ignore the keyboard and the mouse, so nothing you type can race the wizard's own characters into the console. The only way out before it finishes is the toast's Take control! button — it aborts the autoload at once and hands the machine back to you.

Disk and tape images run to several megabytes, so on a slow link the machine can sit silent for a while. A thin Loading N% bar along the bottom of the window shows how much of the image has arrived — during an autoload, a manual boot or a mount alike.

The classic way

1. At the @ prompt, type boot rp1 and press ENTER.
2. BSD 2.11 will autoboot into multiuser mode. Login as root (no password).
3. Try ls, ps -aux, df — or compile a C program with cc.

The boot command is upper case in the manual (BOOT RK1) because that is what works on every console: a Model 33 ASR teletype has no lower-case type at all, so a lower-case command can never reach the machine from it. On a video terminal (VT52 or VT100) lower case works just as well — the guest folds it.

The Front Panel (Panel page)

Every switch, LED, and rotary knob of a real PDP-11/70 is faithfully recreated. The Panel page is where you toggle in a bootstrap loader the way DEC engineers did in the 1970s.

Front panel switch sequences

A simple light chaser — toggle this in to see the address and data LEDs dance:

Switch sequence: HALT, 001000, LOAD ADDRESS
                           012700, DEPOSIT
                           000001, DEPOSIT
                           006100, DEPOSIT
                           000005, DEPOSIT
                           000775, DEPOSIT
                           001000, LOAD ADDRESS, ENABLE, START

Restart the bootloader:

HALT, 120000, LOAD ADDRESS, ENABLE, START

The Bootstrap now! button refuses to start the machine while it is powered off:

The dialog also offers a shortcut to the CONFIG Auto-boot option: tick the checkbox to start the default bootstrap automatically on every future power-on, without visiting the Config page. The choice persists and stays in sync with the CONFIG page checkbox.

The Operator Console

The operator console is what the PDP-11 uses as its TT0: — the machine's own typewriter. Depending on the CONFIG page, it is a Model 33 ASR teletype or one of the two video terminals: a DECscope VT52 (see below) or a DEC VT100.

Model 33 ASR teletype

The console is rendered as an authentic light-cream/beige Model 33 ASR: a paper roll behind the rising sheet, a glass carriage window, and a stamped Teletype Corporation logo on the lower face plate.

• Keyboard. Round dark keycaps with light two-line legends — the base glyph centred, the CTRL-code name or shift symbol above — plus the historical special keys: ESC, LINE FEED, RETURN, DELETE, HERE IS (answerback), REPT (auto-repeat) and BREAK (asserts the console DL11 break condition).
• Upper Case Only. The on-screen keycaps always send upper-case letters. The physical keyboard folds a – z to A – Z only when the Upper Case Only CONFIG option is enabled (off by default, so 2.11 BSD receives lower case).
• Force PDP Output Uppercase. A real Model 33 ASR print mechanism has no lower-case type, so machine output is printed in upper case (on by default) and a loader that writes lower case cannot put those letters on the paper. The punched tape still records the raw byte — reading such a tape in LOCAL prints upper case, while in LINE the original lower case reaches the machine.
• Paper printing. Authentic nroff/man overstrike (^H) rendering: re-printing the same glyph gives bold, underscores give underline, and striking a different glyph leaves the real dark overstrike blot a hard-copy terminal makes.
• Margins. Long lines faithfully jam the carriage at the right margin (72 or 80 columns); characters overstrike the last column instead of wrapping. The paper width follows the selected width so a full line reaches the paper edge. The paper is anchored to the carriage and grows upward out of the top of the machine body; once its edge reaches the top of the window, a scrollbar appears and the view follows the freshly printed line.
• ASR reader/punch. Beside the machine sits the ASR tape reader/punch unit. Every byte echoed to the console punches a matching row of holes on an 8-track paper tape (tracks 1–7 = ASCII, track 8 = parity). As on a real ASR-33 the punch is OFF by default — enable it from the CONFIG page or its own control. Both hanging tapes swing briefly on every step of the mechanism; once a tape reaches the bottom of the window it is scrolled with the mouse wheel (neither tape draws a scrollbar).
• Paper-tape reader. The Load tape button below the machine opens a file dialog and inserts a paper tape into the reader — a raw .ptap (as saved by the punch or the Storage page), a compressed .ptap.zst, or a plain .txt whose characters become 7-bit tape codes. The full tape hangs from the reader slot down to the bottom of the window, its ragged free end torn like the punched tape's — once it reaches the bottom it is scrolled with the mouse wheel (like the punched tape, it draws no scrollbar). As the tape is read it visibly moves up through the slot and shortens, swinging on every byte; when the last byte is read the tape has gone into the machine and a new one can be loaded.
• Reader switch. The four-position switch on the TAPE READER cabinet governs reading: START — runs the reader continuously, sending the tape to the machine at the console speed (authentic ~10 chars/sec or the fast CONFIG pace);
• AUTO — sends one byte and then feeds the next only when the machine's DL11 has accepted the previous one (paused by DC3 / X-OFF, resumed by DC1 / X-ON);
• STOP — pauses;
• FREE — releases the tape and shows the Remove tape from reader button (hidden in every other mode) to pull it out.

Clicking a position label jumps straight to it; clicking the round switch disc itself turns it one detent clockwise (START → STOP → FREE → AUTO), like rotating the real switch.

• CCU knob. The LINE / OFF / LOCAL knob on the apron works the same way: click a label to jump, or click the knob itself to turn it one detent clockwise (LINE → OFF → LOCAL). The CCU routes every read byte exactly like the keyboard: in LOCAL the tape prints on the paper only (a tape-to-paper copy, nothing reaches the machine); in LINE it is sent to the machine and printed by the machine's echo — printing locally too would double every character on echoing guests.
• Duplicating tapes. With the punch engaged (ON), every read byte is also punched onto the output tape — the classic ASR trick for copying tapes (reader in, fresh tape out).

VT52 as the console

When the console terminal is set to a VT52, the operator console becomes a DECscope with its authentic white/grey (P4) phosphor on a black tube — see User Terminals below for the full behaviour, which is shared.

VT100 as the console

Set the console terminal to VT100 and the console becomes a DEC VT100 — the ANSI terminal that succeeded the DECscope. It is drawn in its own cabinet, at its own proportions (the artwork is the terminal's, not a restyled DECscope), and it shares everything that is not the tube itself: the page layout, the zoom button and double-click zoom, the STATE/REBOOT placement and the keyboard handling.

A VT100 is a superset of the VT52, exactly as the hardware was: the DECscope sequences still work and the terminal adds the ANSI grammar (CSI sequences, DEC private modes, scrolling regions, G0/G1 character sets), which it speaks from power-on — a VT100 is a CRT-only machine and has no hardcopy mode to enter first. What never existed on the hardware is refused rather than faked: ESC Y direct addressing, ESC F/ESC G graphics on/off, the VT52 keypad modes and the VT52 identification reply. Asked who it is (CSI c) the VT100 answers VT100 with AVO, and CSI ? 2 h (DECANM) drops it into VT52 compatibility mode, as the real machine did.

Two CONFIG options belong to this terminal alone: the tube phosphor — P4 white, the phosphor the VT100 was introduced on, or P1 green — and the key click (the DECscope's keyboard was mechanical and has no click to make). The VT52 reverse video switch is the DECscope's own and never touches a VT100: there, inverse text comes from the SGR 7 attribute the software sends.

User Terminals (TTY 1 / TTY 2)

Up to two user video terminals (shown only when configured on the CONFIG page) let guest OSes that prefer video terminals run side by side. Each is a DECscope VT52 or a DEC VT100, chosen independently (None | VT52 | VT100), and each is drawn in the cabinet of the terminal you picked — the DECscope's slanted monoblock (an off-white moulded-plastic cabinet with a vent grille, a recessed screen in a deep bezel and a plain side panel with a raised ridge) or the VT100's own enclosure. Input comes from the physical keyboard, as on the original machines.

• Font. Text is rendered in the authentic fritzm/vt52 bitmap display font (monospace is the fallback until the webfont loads).
• Clear screen. Clear screen (ESC E) and form feed (^L) both wipe the display and home the cursor, so clear and multi-page nroff/man output start each page from the top row.
• CRT simulation (optional). A pure-CSS effect adds brightness flicker, scanline shimmer and a vertical-hold roll band.
• Text mode (optional). Renders the terminal as a plain text field instead of the canvas, enabling native text selection and Windows Clipboard (Ctrl+C / Ctrl+V / right-click paste) for fast source-code entry — at the cost of the SGR emphasis rendering.

The LP11 Line Printer (Printer page)

The LP11 is an animated line printer on wide 132-column paper (72/80/100/132 selectable). It has no keyboard — it only prints. Use the Print button to send the accumulated jobs to the real OS printer via the system dialog, or Save.txt to export the output (page breaks are kept as \f markers).

• Speed. Like the real LP11, it echoes characters far faster than the Model 33 ASR console teletype (which keeps its authentic ~33 cps pacing), printing at close to the original's ~300 lines/min.
• DONE handshake. The LP11 honours the historical DONE handshake: writing LPDB clears DONE and re-asserts it as each character is consumed by the mechanism, so a guest print job is throttled at printer speed.
• OFF LINE. When the printer is OFF LINE (or powered off), the controller latches a sticky ERROR flag in LPCS while keeping DONE set — so a guest OS driver reports an error (e.g. ?LP0: I/O error) instead of silently discarding the job.
• Form feed. The LP11 honours form feed (FF, 0x0C) — the 2.11BSD spooler (lpr / lpd) sends FF between jobs so each starts on a fresh page: it fills the rest of the sheet (66 lines at 6 LPI) and closes it with a dashed fold/perforation marker.
• Tabs & paper. The carriage advances to the next 8-column tab stop on TAB, and the paper is sized to the configured print width (centred in the machine body). The cabinet auto-scales down proportionally to fit the window when it gets too small, and the rising fanfold paper climbs the same fraction of the window after scaling.

The VT11 Vector Display (Display page)

An optional DEC VT11 vector-graphics display processor on its own green-phosphor CRT page (1024×768 logical resolution, auto-scaled to fit the window), enabled from the CONFIG page. Lunar Lander uses it — the quick-boot wizard enables the display and switches to the Display page automatically.

Storage (paper tape, disk & tape images)

The Storage page manages every kind of storage media. It has two tabs — Images and Paper Tapes — because the two workflows are completely different. An image is a whole device mounted into the machine and remembered between sessions; a paper tape is a stream of bytes that the reader walks through from the first frame to the end.

Images tab:

• Import image. Drop or pick a disk or tape image here — .dsk, .tap, .ptap and their .zst-compressed forms are supported. While the Storage page is active you can also drop a file anywhere over the window: a full-window drop target appears. A.zst file is a zstd frame and the browser unwraps it on the fly, so a downloaded image needs no unpacking first.
• The file name is the device name. An image is mounted under the device URL taken from the file itself: RP1.DSK.ZST becomes rp1.dsk, which is why the guest boots it with boot rp1. Rename the file to the unit you want to use — or leave the name alone and bind the image to a drive afterwards (see below). The table below maps every device to its drive, its controller and its boot command.
• Mounted images — the list, Unmount and the drive binding. The list names the images mounted in this browser. The counter next to it counts the images you mounted (dropped or imported), not the ones the desktop build carries inside itself. With an image selected, Unmount removes it; "Assign to drive" binds it to a drive (rk0-rk7, rl0-rl3, rp0-rp4, ra0-ra3, tm0-tm2), so the guest boots it from there, and "— not bound —" detaches it, returning the drive to the file-name convention. An image whose size does not fit the chosen controller (an RP06 image on an RK05-only RK11) is refused unless you press "Assign anyway". Mounted images live in browser storage (IndexedDB) and are re-mounted automatically on the next launch.
• Export image. Downloads a stored image — guest-OS writes included — to your machine. Each entry states its state: "no changes", "N blocks changed", or "not mounted, N blocks changed".
• Persistent disk changes. Guest-OS writes are saved to browser storage and overlaid on the base image on the next launch, so files an operating system created are still there tomorrow. Only the blocks the guest actually wrote are kept — the base image is fetched again on every launch — and a saved block always wins over the pristine one. They are written out periodically and when you leave the page, and they belong to one image: Reset image discards them for the selected disk, Reset all for every disk, which returns the media to its factory state.

Which file is which device:

Paper Tapes tab:

• Paper tape reader file. A selector for the reader (#ptr) holding the tapes this build ships — BASIC-11 V007A, ODT-11X-V004A, ED-11-V004B, Lunar Lander and the bootstrap loader — plus any.ptap you dropped. Load one and boot it with BOOT PR.
• Rewind tape and the tape state. The indicator beside the button says whether a tape is loaded and how far the reader has moved through it; Rewind tape puts it back to the first frame, which is what a guest does when it restarts a read.
• Import paper tape. A small drop zone accepting .ptap and .ptap.zst — dropped tapes are added to the reader file selector.
• Export paper tape. The punch buffer is filled by the bytes the console echoes, and the counter shows how much is on the tape. Download saves it as a.ptap; Clear empties the buffer for the next tape.

Note: the paper-tape reader is driven by the console bytes — every byte echoed to the console

punches a matching row of holes on the ASR paper tape.

Machine State (STATE button)

The round STATE button (top-left corner, right of REBOOT) opens the machine-state dialog — a full save/restore of the emulated PDP-11, not just the CPU: registers, memory, every I/O device (console, terminals, printer, disks, tape and the paper-tape reader/punch), the paper in the teletype and LP11, the video-terminal screen contents (VT52 and VT100 alike) and even the VT11 vector-display picture are all captured. Think of it as a save file of the whole machine.

• Save state — captures the machine exactly as it is right now under an auto-generated name (date and time). The hardware configuration is part of the state: restoring it re-applies the console type, user terminals, printer and VT11 display, restarting the machine to match.
• Load — restores the selected state and restarts the machine; a confirmation asks first. States saved by older versions of the emulator keep working.
• Rename / Delete — organise the list or remove states; the counter next to the list shows how many states you have.

The STATE button mirrors REBOOT and is available on the Panel, Console (teletype, VT52 or VT100) and TTY pages. States are stored in the browser's IndexedDB and survive reloads and sessions.

Configuration (Config page)

The Config page controls the emulated peripherals and is persisted between sessions. The form is split into four tabs, with the Apply and Restore defaults actions in a bar below the tabs:

Leaving the Config page with uncommitted changes asks for confirmation, so nothing is lost silently:

Structural changes (console type, terminals, printer, VT11 display) are committed with Apply, which restarts the machine so the emulated hardware matches the configuration. Print widths, teletype speed, the Upper Case Only and Force PDP Output Uppercase flags, key click, reverse video, CRT effects, VT52 text mode, machine hum and the photo backdrop apply immediately. Restore defaults fills the form with factory values (committed by Apply); the four live BEHAVIOUR options — Reboot confirmation, Help Me! sticker, Machine power and Auto-boot — are reset to their factory values immediately, without waiting for Apply (the machine powers down, since the factory state is off).

The hum is synthesized with Web Audio on its own audio channel, so it never cuts off the teletype/printer or the VT100 key-click sounds.

Guest Operating Systems

The emulator ships with ready-to-boot disk and tape images. Just type boot <device> at the @ prompt at the @ prompt — or pick one with the magic wand. In a build with a reduced image set (e.g. the Minimal desktop variant), rows whose image is not shipped are dimmed and marked image not in this build — the table shows exactly what can boot here.

Buttons, Shortcuts & Indicators

Switching pages

Use the sidebar to switch between:

• Panel — the front panel with switches and LEDs.
• Console — the operator console: a Model 33 ASR teletype, or a DECscope VT52 / DEC VT100 when the console terminal is a video terminal.
• TTY 1 / TTY 2 — user video terminals (VT52 or VT100), shown only when configured.
• Printer — the LP11 line printer page, shown only when configured.
• Display — the VT11 vector-graphics CRT page, shown only when configured.
• Storage — storage media in two tabs: Images (drop zone, mounted images) and Paper Tapes (reader, punch export).
• Config — configure the emulated peripherals (persisted between sessions).
• Info — detailed instructions, OS reference and the About block (version, website, author and license; the version marker at the bottom of the sidebar opens this page).

Floating controls

Sidebar activity lamps

Each output sidebar button has a small blinking green LED in its top-right corner: it pulses while the PDP-11 writes output to that console/terminal (and blinks for the whole print job on the Printer button), then switches off about half a second after the output stops.

Troubleshooting

An image cannot be loaded

If a guest OS image cannot be fetched completely — a big BSD image dropped by the hosting server mid-download, or an image that is not bundled in the Minimal desktop build — the emulator doesn't stall silently. A dialog in the same shared modal style as the first-run hint explains that the image is incomplete and offers Open Storage, which jumps straight to the drop zone for a manual drag & drop of the downloaded file.

The wording adapts to the environment: a page opened as a local file:// explains that the browser blocks fetching the media directory (and suggests a local web server), while the Tauri Minimal build explains that the image is not shipped and points to the drop zone.

A snapshot is refused after an image update

A snapshot stores the machine's memory and registers, not the disk image itself: on restore it is layered back onto whatever disk the emulator currently ships. If that disk has been updated since the snapshot was taken, the two no longer match — the guest's file system in memory would not describe the disk underneath it, which shows up as a corrupted file system rather than as anything obvious.

The emulator detects this and refuses the restore instead of corrupting the disk. It names the image and both builds, and offers to delete the snapshot:

Take a fresh snapshot on the current build, or delete the stale one — a snapshot cannot be migrated onto a disk it was not taken from.

The Desktop App

Prefer a native app? The same emulator is packaged as an offline desktop application for Windows x64 and Linux with Tauri. Two installer variants are available:

On Linux the installation size for every configuration may be substantially larger (it depends on the package format).