# M/PC – A Concatenative OS

> Source: <https://wiki.xxiivv.com/site/m_pc.html>
> Published: 2026-07-06 20:08:46+00:00

## •/PC

M/PC is a [concatenative](concatenative.html) operating system for [Varvara](varvara.html), inspired by [Openfirmware](https://en.wikipedia.org/wiki/Open_Firmware), designed to manage files on system without a file browser. It uses the postfix notation, meaning that the function success their operands:

```
( Get the number of bytes in folder/file_name )
folder/ file_name cat len dec
```

Files can store reusable sequences of commands, the tilde prefix includes the content of the file:

```
( Content of ./show-slide )
slide_ swp cat 3cx22.icn cat 1 icn
1 ~show-slide
```

The interface uses a single prompt at the top of the screen to input commands:

### Controls

The operating system can be used largely without a keyboard to navigate folders and launch roms:

`left/right` Navigate Stack`up/down` Scroll Stack`A` Evaluate Selected Symbol`B` Directory/Back

### Kiosk

To start M/PC as a BIOS rom so that when the user presses `F4`, Varvara returns to the BIOS instead of triggering a reboot, launch with arguments:

```
uxnemu m_pc.rom orca.rom run
```

### Wallpaper

On boot, M/PC will try and draw an [ICN file](icn_format.html) named wallpaperWWxHH.icn, where `WW` is the width of the screen divided by 8 in hexadecimal, and `HH` the height.

### Reference

Here is the list of all primitives:

```
dir ( -- [f] )
	Put the file names in the current location on the stack.
mov ( path -- [f] )
	Move the current location to current/path, then do dir.

now ( -- date time )
	Puts the date Tue, 23 Jun 2026, and time 11:48:45 on the stack.

run ( f.rom -- ok )
	Run the rom file, return with F4.
icn ( f.icn blend -- ok )
	Draw an icn file with blend.
txt ( f.txt line -- ok )
	Read a text file starting at line.

len ( f -- hex )
	Put the length of a file in hexadecimal.
put ( body f -- ok )
	Create a file with the content of body.
get ( f -- body )
	Put the content of a file on the stack.
cpy ( fsrc fdst -- ok )
	Copy the content of fsrc into fdst.
era ( f -- ok )
	Erase file.
ren ( fsrc fdst -- ok )
	Rename file fsrc into fdst.

pop ( a -- )
	Pop symbol at the top of the stack.
dup ( a -- a a )
	Duplication symbol at the top of the stack.
ovr ( a b -- a b a )
	Copy second symbol to the top of the stack.
swp ( a b -- b a )
	Pull the second symbol to top.
rot ( a b c -- b c a )
	Pull the third symbol to top.

add ( a b -- a+b )
	Push the sum of two symbols.
sub ( a b -- a-b )
	Push the difference of two symbols.
dec ( hex -- dec )
	Convert hexadecimal number to decimal.
hex ( dec -- hex )
	Convert decimal number to hexadecimal.
cat ( a b -- ab )
	Concatenate two symbols.

cmp ( a b -- bool )
	Compare the names of two symbols.
and ( a b -- bool )
	Put true if both symbols are true.
ora ( a b -- bool )
	Put true if either symbol is true.

rsz ( width height -- )
	Resize the screen, puts true if resize is supported by Screen.
out ( a -- )
	Output symbol to Console/write.
bye ( -- )
	Quit.
```

[Source](../etc/m_pc.tal.txt), Latest[Repository](https://git.sr.ht/~rabbits/m_pc)**Support:**[Manifest](manifest.html)[Theme](theme.html)[Snarf](snarf.html)

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