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---
title: SYSTEM.CNF
type: format
summary: System designation file that names the program to start from a disc.
category: File formats
category: System software
info: File name = SYSTEM.CNF
info: Location = Root directory of the disc
---

## Overview

SYSTEM.CNF is Sony's system designation file. It describes the PlayStation system settings and the application that is to be started.[^os23] The kernel reads the file at boot time and uses it to reserve memory for the stack, the tasks and the events.[^lo203] The [PS-X OS](/system/ps-x-os/) first checks the type of disc in the CD-ROM drive, and only an appropriate disc has its SYSTEM.CNF read and the named program executed.[^os23] The [boot](/system/bios/boot/) page describes the whole sequence.

## Syntax

Each parameter is described from the beginning of a line in `<key word> = <content>` format. All characters are 1-byte uppercase alphanumerics, and lowercase characters may not be used. A space is necessary on both sides of the equal sign. When the same parameter appears more than once in a file, the first one found takes precedence.[^os23] The TCB and EVENT values are written in hexadecimal.[^lo203]

## Keywords

The parameters that may be described are shown below.

Table: System designation file keywords

| Key word | Contents | Default | Minimum | Example |
| --- | --- | --- | --- | --- |
| BOOT | Device name, file name and version of the boot executable[^lo203] | cdrom:PSX.EXE;1 | | BOOT = cdrom:\SLUS_123.45;1 |
| TCB | Number of task control blocks (hex) | 4 | 1 | TCB = 5 |
| EVENT | Number of event control blocks (hex) | 0x10 | 0 | EVENT = 5 |
| STACK | Stack pointer value when the BOOT file starts | 0x801FFF00 | 0x8010000 | STACK = 800FFF0 |

The PlayStation Operating System manual gives the STACK default as 0x8001FF00.[^os23] The Run-Time Library Overview and psx-spx both give 0x801FFF00, which is 256 bytes below the top of 2 MB of memory in segment B.[^lo203][^spxcnf]

## Limits

The number of task control blocks and event control blocks that can be allocated is limited by the formula TCB * 192 + EVENT * 32 + 544 < 4096.[^lo203] The BIOS itself opens 5 events for its CD-ROM functions. Consequently, of the 16 events given by the default EVENT = 10, only 11 are available to the game.[^spxev]

## Boot Argument

The BOOT line may carry an argument string after the file name. The BIOS copies this string to the 128-byte area at address 0x00000180, where the executable may read it.[^spxcnf][^spxmap]

## Boot File Name

Licensed games name the boot executable after the product code printed on the case. Because ISO 9660 level 1 allows only 8 characters in a base name, the minus sign is replaced by an underscore and the last two digits move into the extension, so SLUS-12345 becomes SLUS_123.45.[^spxcnf] The suffix ";1" is the ISO 9660 file version number. When a disc has no SYSTEM.CNF, the BIOS boots the file PSX.EXE instead.[^spxcnf]

## Example

A typical SYSTEM.CNF reads as follows.[^spxcnf]

```
BOOT = cdrom:\SLUS_123.45;1
TCB = 4
EVENT = 10
STACK = 801FFF00
```

## References

[^os23]: Sony Computer Entertainment Inc. PlayStation Operating System. August 1998. Page 2-3, Table 2-1.
[^lo203]: Sony Computer Entertainment Inc. Run-Time Library Overview. January 1999. Page 2-3, Table 2-1.
[^spxcnf]: psx-spx. CDROM File Formats, SYSTEM.CNF. https://psx-spx.consoledev.net/cdromfileformats/
[^spxmap]: psx-spx. Kernel (BIOS), BIOS RAM Map. https://psx-spx.consoledev.net/kernelbios/
[^spxev]: psx-spx. Kernel (BIOS), B(08h) OpenEvent. https://psx-spx.consoledev.net/kernelbios/