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iAltairHD pretends to be a MITS Altair 8800 computer and gives you a glimpse how old operating systems like CP/M 2 have felt. It is fully loaded with software but please note that the system is completely self contained and this means that you cannot remotely add any code. iAltairHD dir screen

Quick Start - How to play Zork, Startrek or Eliza or some classic Basic games

  • Boot CP/M 2 - this is the default system to boot.
  • For Zork: Type "zork" at the "A>" prompt.
  • For Startrek: Type "mbasic startrek" at the "A>" prompt.
  • For Eliza: Type "mbasic eliza" at the "A>" prompt.
  • For a collection of classic Basic games: Type "g:" at the "A>" prompt and then "mbasic menu" at the "G>" prompt. Then choose the game you want to play - note you must enter the name in upper case letters.

Boot Button

Starts the system selected in the list.

Restore Button

Restores the system selected in the list below and starts it. This is useful in case you have accidentally deleted some important files. Use the Boot or Restore button also in case you see the message "Execution terminated. Boot or Restore to resume.". Note that in CP/M 2 and CP/M 3 there are some originally empty disks which will not be restored to their empty state. If you want to erase them, use the "XFORMAT" or "ERA" command.

Keyboard Button

Brings the keyboard to the front so that you can interact with the system. The keyboard disappears when you touch the screen (upper) section of the application.

FontColor Button

Brings up a pop over window to set the font color to amber, green, white or a custom defined color where you can specify the Hue/Saturation/Brightness property of the desired color.

Spread / pinch gesture

In the portrait orientation you can increase the terminal screen and font size using the spread gesture. You undo this effect with the pinch gesture. iAltairHD Pascal screen

Maximum Speed Switch

Typically the simulated CPU runs as fast as possible. For some games however it is useful to limit the simulated CPU frequency. Set "Maximum Speed" to "OFF" in this case and the simulated CPU will run with a clock frequency of about 4 MHz. Also note that this feature is only supported for the 8080 and the Z80 CPU. The 8086 CPU will always run at maximum speed.

iAltairHD ladder screen

Config button

This brings up a pop over window to set the character sequences sent by the cursor control buttons (up, down, left, right). You can choose from a set of predefined values supporting Turbo Pascal (Turbo), WordMaster (WM), WordStar (WS), SuperZap (Zap), Perfect Writer (PW), Ladder (Ladder) or you can define your own settings (User). Note that the caret character (^) is used for specifying control characters, e.g. ^X stands for Control-X. If there is a need to use the caret character by itself, you can use ^^.

Supported Systems

  • Altair 4K Basic is the famous 4k Basic. Note that the underscore character ("_") can be used to cancel the last character entered, i.e. "PRINT 199_8" will print 198.
  • Altair 8K Basic is an extended Basic. iAltairHD Altair 8K Basic
  • Altair DOS was a Disk Operating System. Type "MNT 0" to mount disk 0 and "DIR 0" to view the contents of this disk. Altair DOS comes with two disks, so "MNT 1" will work as well. You can also use the FORTRAN compiler.
  • CP/M 2 was a popular operating system. Type "DIR" to get an overview of the files available. In order to switch to another disk, type its disk character followed by :, i.e. "F:" brings you to disk F. On disk B: you will find the Pascal MT+ compiler and a Prolog interpreter with source code. Disk C: has Wordstar the leading word processing software at its time and VEDIT another screen oriented editor. Disk D: features Multiplan, a spread sheet application. Disk E: has Turbo Pascal and disk F: contains some games including the text based Zork adventures. Disks G: and H: are a collection of classic Basic games from Creative Computing. The disks I:, J:, K: and L: are empty and can be used freely. Also note that these disks will not be wiped when you restore the system with the Restore button. Also note that disk I: and J: correspond to disks C: and D: of CP/M 3. This is useful if you want to exchange data between CP/M 2 and CP/M 3. On disk M: is dBASE II (Ver 2.4, 1 April 1983) a popular data base management system at its time.
  • CP/M 2 without MMU runs CP/M 2 on a system without a Memory Management Unit. This allows a faster CPU but you must run at Maximum Speed.
  • CP/M 3 was a successor of CP/M 2 supporting banked memory. Note that disks C: and D: are not wiped during restore and that they correspond to disks I: and J: in CP/M 2 respectively. This is useful if you want to exchange data between CP/M 3 and CP/M 2.
  • CP/M 86 is CP/M for the 8086 processor. On disk B: there is VEDIT and the Pascal MT+86 compiler. iAltairHD CP/M 86 screen
  • MS-DOS 1.25 is an early version of MS-DOS. Note that disk B: is not wiped when you restore the system with the Restore button.


In case the system does not respond any more you can use either the Boot button or the Restore button. Some application programs also terminate when a Control-C character is typed.


Please be aware that because of iCloud restrictions only fully user generated data can be backed up. Therefore the simulated disks are not backed up via iTunes or iCloud.

Dropbox Integration: Backup and Sharing

The Dropbox integration allows you to backup the CP/M disks I:, J:, K: and L: to your Dropbox (in the folder /Apps/iAltairHD) and to share the backup with other instances of iAltairHD linked to the same Dropbox account. The following functions are supported using the Dropbox button:

  • Link allows you to link iAltairHD to your Dropbox account.
  • Unlink allows you to unlink iAltairHD from the Dropbox account it is currently linked to.
  • Backup to Dropbox creates resp. updates your backup on Dropbox. It creates a space optimized archive of the CP/M disks I:, J:, K: and L:.
  • Restore from Dropbox restores the CP/M disks I:, J: K: and L: from the latest version found on your Dropbox.
  • Cancel all requests stops all current Dropbox requests such as backup or restore.

iAltairHD Dropbox menu

More Information

See schorn.ch for more information regarding the SIMH AltairZ80 simulator for other platforms such as Macintosh, Windows, Linux and Zaurus.

Appendix: Usage of the FORTRAN compiler in Altair DOS

User input is in green.
.MNT 0 Make disk 0 available (mount)
*P Display the program source code
*Q Quit the editor without saving any changes. With D nnn you can delete line nnn and with I nnn you can insert a line with line number nnn. Use N to renumber the lines and E to exit the editor with saving the changes.
.F80 Start the FORTRAN compiler
*=&FTEST Compile FTEST
Push the Boot button Restarting the computer quits the FORTRAN compiler
.MNT 0 Make disk 0 available (mount)
.L80 Start the linker
*&FTES Note that the name of the REL file is FTES not FTEST
*FORLB/S Search the FORTRAN runtime library
*/E Quit the linker
.SAV FTEST 0 Save the result
ENTER LOW ADDRESS 017100 This is the first number from Data 017100 031764
ENTER HIGH ADDRESS 031764 This is the second number from [017111 031764 22]
ENTER START ADDRESS 017111 This is the first number from [017111 031764 22]
.FTEST Run the program