# System (Machine)

The **System** tab controls which machine kat5200 emulates and how it is
configured. Use **Save** to update your global defaults, or **Save for ROM only
[*]** to apply the settings only to the currently selected ROM.

## System

Choose the emulated machine:

- **Atari 5200**
- **Atari 400/800**
- **Atari XL/XE**

The options below change depending on the selected system (for example, RAM,
BASIC, and SIO-patch settings apply only to the 8-bit computers).

## OS / BIOS

| Setting | Description |
|---------|-------------|
| **OS** | The OS / BIOS variant to boot. The choices depend on the machine: for the 5200, **4-Port** or **2-Port**; for the 400/800, **OS A** or **OS B**; for XL/XE, a specific OS revision (600XL, XL/XE, 800XE, XEGS, 1200XL, …). |
| **BIOS File** | Path to the OS / BIOS ROM image on disk, with a file browser. |

The OS file is also filled automatically when you scan for BIOS images in the
[Setup](misc.md#setup) window. Changing the OS or TV standard re-resolves and
reloads the matching BIOS file.

## Media files

| Setting | Description |
|---------|-------------|
| **Cartridge** | The cartridge image attached to the machine (file browser). |
| **BASIC File** | The BASIC ROM file (8-bit only). |
| **Disk File** | A floppy disk image to attach (8-bit only). |

## Memory and video standard (8-bit)

| Setting | Description |
|---------|-------------|
| **RAM** | Amount of RAM to emulate (e.g. 16 / 48 / 64 / 128 KB). Valid amounts depend on the selected machine. |
| **TV Encoding** | **NTSC** or **PAL**. Affects timing, speed, and colors. |

## 8-bit options

| Setting | Description |
|---------|-------------|
| **Enable SIO Patch** | Speeds up loading of floppy and cassette images. Fast and convenient, but not compatible with every title — disable it if a disk/cassette image fails to load. |
| **Enable BASIC** | Boots the machine with BASIC enabled. Most cartridges expect BASIC **off**; some titles (and, of course, BASIC programs) require it **on**. Best left off globally and enabled per-ROM. |
| **BASIC Rev** | Which revision of the BASIC ROM to use (Rev A / B / C). |

## Controller ports

**Port 1**–**Port 4** select which kind of Atari controller is emulated on each
port:

- **None**
- **Joystick**
- **Trackball**
- **Paddles** (8-bit)
- **Keypad** (8-bit)

The 5200 offers Joystick / Trackball; the 8-bit computers add Paddles and Keypad.
The detailed PC-to-Atari bindings live in [Options → Input](input.md); this only
selects the controller *type*.

## Pokey POT Values

The **Pokey POT Values** sub-window exposes the low-level analog pot calibration
used by the emulated POKEY — **Joystick HPOT/VPOT Center**, **Low**, and
**High** for the joystick's horizontal and vertical pots, plus (on the 5200)
**Trackball HPOT/VPOT Center** and the **Trackball DPOT Min/Max** range. These
are advanced
tuning values; most users never need to change them. They matter when fine-tuning
how an analog controller maps onto a specific game's expected pot range.

!!! tip
    If a game misbehaves, the most common System-level fixes are toggling **Enable
    BASIC**, toggling the **SIO Patch**, or correcting the **RAM** amount. For
    cartridge mapping problems, set the **Mapping** per-ROM in the
    [Launcher](../launcher/rom-settings.md).
