IBM 1401 Emulator in Swift

This project is some very early and inclomplete version of an IBM 1401 emulator written in Swift.

While studying the machine and finishing a simple hello world punch card code, it was hard for me to test my code as there are not many emulators for the machine and I was not able to make simh run at this time.

With the help of the amazing emulator of https://rolffson.de I was finally able to punch and run my code virtually on his software. Unfortunately, the project is only availble for Microsoft Windows and more a 3D simulation than a convinient emulator, so I descided to write my own...

⚠️ The whole emulator is incomplete. For now, not all opcodes are implemented and reading external files into the storage is not finished.

> Image: https://upload.wikimedia.org/wikipedia/commons/c/cb/BRL61-IBM_1401.jpg

More information about the machine itself: http://ibm-1401.info

Requirements

The code should run on any system that supports Swift 5.7 and higher.

The emulator depends on lib1401

Manual

Usage

Inside the project directory run: swift run

to start an emulator. You will be welcomed with a prompt where you can enter commands.

Emulator commands

Load program (l / load)

You can load external files with punch card code when providing an absolute path to the load command.

Example: l /some/absolute/path/to/a/file.cd

Without any file name a default hello world program will be loaded.

Start / Step (s / start)

This command emulates pressing the IBM 1401 start button in single step mode.

Run (r / run)

This command emulates pressing the IBM 1401 start button in run mode.

Dump storage (d / dump)

This command dumps the complete storage. Note that the output is in BCD mode.

Monitor (m / monitor)

This command dumps all registers and contents.

Reset (rst / reset)

Terminate execution cycle, reset core storage and registers. This command allows you to load and run another program.

Quit (q / quit)

Quit the emulator

Features

• Load arbitrary program from external file

• Parity and validity checks for registers

• Normal 1401 opcodes:

  • Set Word Mark (,)
  • Clear Storage (/)
  • Move (M)
  • Move Digit (D)
  • Move Zone (Y)
  • Halt (.)
  • Halt and branch (.)
  • No Operation (N)
  • Load (L)
  • Write a line (2) - Partially implemented
  • Clear word mark ())
  • Divide (()
  • Modify address (=)
  • Zero and add (&)
  • Add (A)
  • Branch or branch on indicator (B)
  • Compare (C)
  • Move numerical / digit (D)
  • Move characters and edit (E)
  • UNDOCUMENTED / UNCLEAR (G)
  • Zero and substract (-)
  • Move characters to record or group (P)
  • Subtract (S)
  • Branch if word mark and/or zone (V)
  • Move characters and supress zeros (Z)
  • Read a card (1)
  • Read a card and branch (1)
  • Write and read (3)
  • Punch a card (4)
  • Read and punch (5)
  • Write and punch (6)
  • Write, read and punch (7)

• Optioal opcodes:

  • Multiply ( )
  • Store B-Address register (H)
  • Store A-Address register (Q)
  • Branch if bit equal (W)
  • Move and insert zeros (X)
  • Start read feed (8)
  • Start punch feed (9)

• Tape:

  • Control unit (U)

• Printer:

  • Control carriage (F)

• Bits:

  • Move zone (Z)

  • Special:

    • Select stacker and other device controls (K)

  • 1460-Features:

    • Translate (T)