JNEXT
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Using your own image

If you already have a NextZXOS SD-card image, point JNEXT at it:

jnext --sdcard /path/to/my-image.img

An explicit --sdcard always wins: it is used as-is, and no download is ever offered or performed. In the graphical version you can set a permanent default in Preferences (chapter 4), and change the card while JNEXT runs (below).

The image is opened read-write, and whatever the emulated machine writes to the card is kept. Booting is not one of those things: reaching the NextZXOS welcome screen and the menu writes nothing at all, and leaves the image byte-identical. What changes it is file work done through NextZXOS — saving from NextBASIC, a DOS command such as .mkdir, the Browser copying or deleting something, or a program writing a file. Those changes persist into later runs, exactly as they would on a real card, so two runs sharing one image are not independent once one of them has written.

Add --sdcard-readonly when a run must not disturb the image: the emulated machine then sees a write-protected card and the host file is never touched.

Changing the card while JNEXT runs

File > Insert SD Card Image puts a different card in the running machine, and File > Eject SD Card takes it out. Nothing is reset, so you keep what you were doing — a RAMdisk, say, while you copy files from one card to another.

The Next has no way to notice a card being pulled, so NextZXOS has to be told: type REMOUNT. It answers Remove/insert SD and press Y; change the card from the File menu, then press Y. NextZXOS reads the new card and lists its drives again.

A few things to know:

  • The inserted card is write-protected if JNEXT was started with --sdcard-readonly, like the first one. It does not become your saved default; that is Preferences' job.
  • The machine keeps the ROMs it started with — a real Next loads them once, at power-on. A hard reset, or loading a program, reads them from the card that is in. After an eject, those put the last inserted card back, since JNEXT cannot start a machine without one.
  • The card cannot be changed while an RZX recording is being made or played, or while a directly loaded .nex keeps its own file open. JNEXT says why.
  • Changing the card clears the debugger's rewind history.
  • A .jns snapshot saved with one card refuses to load once a different card is in (chapter 5, Snapshots). A copy of the same card is the same card to it.