SID file header (PSID and RSID)

A SID file is a header followed by C64 code and data. The header’s numbers are big-endian, unlike the C64’s own. Offsets are hexadecimal, written with a + as in the format’s own document, SID_file_format.txt from the High Voltage SID Collection, which this page follows (the copy dated 9 October 2026). Addresses use the C64’s $ notation. Versions 1 to 5 exist, and each adds to the one before.

Common fields

Offset	Size	Type	Name	Description
+00	4	ASCII	magicID	`PSID`, or `RSID` for a tune that needs a real C64 environment.
+04	2	u16	version	1 to 5. RSID, and PSID V2NG, must be 2 to 5.
+06	2	u16	dataOffset	`0076` for version 1, `007C` for versions 2 to 5.
+08	2	u16	loadAddress	`$0000` to `$FFFF`. If `$0000`, the first two bytes of the data give the load address, little-endian, and are not loaded. RSID must use `$0000`.
+0A	2	u16	initAddress	Where to start. The accumulator holds the song number minus one.
+0C	2	u16	playAddress	Where to call for each play step. `$0000` means the program installs its own interrupt handler. RSID must use `$0000`.
+0E	2	u16	songs	Number of songs, 1 to 256.
+10	2	u16	startSong	The default song, 1 to songs.
+12	4	u32	speed	RSID must be 0.
+16	32	text	name	Windows-1252, with a zero byte at the end if shorter than 32 bytes.
+36	32	text	author	The same encoding.
+56	32	text	released	Formerly “copyright”. The same encoding.
+76	…	bytes	data	Version 1 data starts here.

00000000  50 53 49 44 00 02 00 7C 10 00 10 00 10 03 00 01  PSID...|........
00000010  00 01 00 00 00 00                                ......

The start of a constructed version 2 file: load and init at $1000, play at $1003, one song, VBI timing

Speed

One bit per song. A bit that is 0 means VBI timing (50 Hz on PAL, 60 Hz on NTSC); a bit that is 1 means CIA 1 timer A timing, which is 60 Hz by default. Bits 0 to 31 give songs 1 to 32.

Case	Beyond song 32
Version 1, or versions 2 to 5 with the PlaySID flag set	The pattern repeats: song 33 uses bit 0.
Versions 2 to 5 with the PlaySID flag clear	Bit 31 applies to song 32 and all later songs.

Surplus bits should be 0.

Version 2 and later

Offset	Size	Type	Name	Versions	Description
+76	2	u16	flags	2–5
+78	1	u8	startPage	2–5	Start of free memory, in pages.
+79	1	u8	pageLength	2–5	Number of free pages.
+7A	1	u8	secondSIDAddress	3–4 (0 in 2)	Address of a second SID.
+7B	1	u8	thirdSIDAddress	4 (0 in 2–3)	Address of a third SID.
+7C	…	bytes	data	2–5	C64 data.

In version 5, +7A and +7B are replaced by the multi-SID fields.

Flags (+76)

Bits	Name	Values
0	MUS player	0 built-in player. 1 Compute!’s Sidplayer MUS data, which needs an external player.
1	PlaySID or BASIC	PSID: 0 C64 compatible, 1 PlaySID-specific. RSID: 0 C64 machine code, 1 C64 BASIC.
2–3	Video standard	00 unknown, 01 PAL, 10 NTSC, 11 PAL and NTSC.
4–5	SID model	00 unknown, 01 MOS6581, 10 MOS8580, 11 both.
6–7	Versions 3–4: second SID model. Version 5: panning layout.	Model as bits 4–5; unknown means the same as the first SID. Panning values below.
8–9	Version 4: third SID model. Version 5: panning mode.	Model as bits 4–5. Panning values below.
10	Embedded lengths (v5)	0 lengths may be stored elsewhere. 1 a length table follows the payload.
11	FM OPL (v5)	0 not required. 1 an FM OPL chip is required; `$DF00` to `$DFFF` is reserved and no SID may be mapped there.
12–15		Reserved, 0.

startPage and pageLength

startPage	Meaning
`00`	The tune does not write outside its data range, so the free range can be worked out from the load address and data length.
`FF`	No free page exists; a driver cannot be relocated into the tune.
other	The first page of the largest free range. For example, `1E` means `$1E00`.

pageLength is the number of free pages from startPage, and must be 0 when startPage is 00 or FF. The free range should not overlap the data’s load range. For RSID, it should not overlap the ROM areas ($A000–$BFFF, $D000–$FFFF) or $0000–$03FF.

Extra SID addresses

In versions 3 and 4, each byte is the middle byte of an address $Dxx0. Only even values 42 to 7E and E0 to FE are valid (42 is $D420, FE is $DFE0). Any invalid value, including 0, means there is no such SID. The third SID’s address must differ from the second’s.

Version 5

Metadata

In version 5 the three text fields (+16, +36 and +56, 96 bytes in all) can be one block holding three non-empty strings, each ended by a zero byte, in Windows-1252. The name always starts at +16. Readers try this form first and fall back on the fixed 32-byte fields. When all three strings fit in 32 bytes, writers keep the author at +36 and released at +56.

Multi-SID fields

Offset	Name	Description
+7A	multiSidConfig	0 for a single SID. Bits 0–3: total SIDs including the first, 2 to 15. Bits 4–7: address configuration.
+7B	sidAddressConfigStart	The base address for SID 2, encoded like the extra SID addresses, or 0 for the standard start. Must be 0 for a single SID. Any invalid value is treated as 0.

Bits 4–7	Steps	Max SIDs at the default start
0	+`$20`	15
1	+`$40`	15
2	+`$80`	12
3	+`$100`	6
4	Alternating +`$20`, +`$60`	15
5	Alternating +`$20`, +`$E0`	12
6	Alternating +`$100`, +`$300`	4
7–15	Reserved

SID 1 is always at $D400, and addresses may only be in $D400–$D7E0 and $DE00–$DFE0. A file that asks for more SIDs than the addresses allow must be rejected.

Panning

Bits 6–7 (layout)	Meaning
00 Standard	One SID is centred; several alternate left and right, starting left.
01 L/C/R	One SID is centred; several alternate left, centre and right, starting left.
10 Center First	The first C-count SIDs are centred; the rest alternate left and right.
11 Fully Centered	Every SID is centred.

Bits 8–9 (mode)	Meaning
00 Direct	Uses the layout unchanged.
01 Reverse	Mirrors the layout from left to right.
10 Group	Groups consecutive panning assignments.
11 Spread	Distributes SIDs across the available positions.

Song length table

When bit 10 of the flags is set, the last songs × 4 bytes of the file are a length for each song in order, excluded from the C64 data. Each entry is two big-endian words: BCD minutes and seconds (MM:SS), then BCD milliseconds, whose most significant digit must be 0.

.SID File Format – Header