c64-disk

name

c64-disk

description

Using a Commodore disk drive (1541 and family) from the Commodore 64: device 8, LOAD/SAVE, listing the directory, the command channel (channel 15) for DOS commands (NEW/format, SCRATCH, RENAME, COPY, INITIALIZE, VALIDATE), reading the error/status channel, and file types (PRG/SEQ/REL/USR). Use this skill WHEN a user asks "how do I show a disk directory", "LOAD a program from disk", "what's the difference between LOAD\"NAME\",8 and ,8,1", "how do I format/scratch/ rename a disk file", "what is OPEN 15,8,15", "how do I read the disk error channel", or mentions device 8, the 1541, or a .d64. Pairs with c64-io, c64-tape, and c64-kernal.

C64 Disk Drives (1541 and family)

The disk drive is serial-bus device 8 (8–11 for multiple drives). It is an intelligent peripheral with its own 6502 and DOS, so the C64 talks to it with high-level commands rather than driving the medium directly. Two things you do constantly: read/write program and data files, and send DOS commands down the command channel.

Honesty note: the Commodore 64 Programmer's Reference and User's Guide are thin on 1541 internals. They cover LOAD/SAVE, sequential files, and point you at the disk drive manual for DOS specifics. Track/sector layout, GCR encoding, BAM, and the full DOS command syntax are not in these manuals — the command syntax below is the well-known standard 1541 DOS set, included so the skill is useful, but for authoritative detail use the 1541 User's Manual / "Inside Commodore DOS".

Loading and saving programs

LOAD "NAME",8        : REM load a BASIC/PRG file (relocates to BASIC start, $0801)
LOAD "NAME",8,1      : REM load to the address it was SAVEd from (ML, data, hi-res)
SAVE "NAME",8        : REM save the current BASIC program
VERIFY "NAME",8      : REM compare disk file against memory
LOAD "*",8           : REM load the first file in the directory
LOAD "PART*",8       : REM pattern match: first file starting "PART"

The secondary address is the load-vs-relocate switch, and it's the single most common confusion:

• ,8 (sa 0, the default) → BASIC relocates the program to the start of BASIC ($0801). Use for BASIC programs.
• ,8,1 (sa 1) → loads to the original address the file was saved from. Use for machine-language routines, sprite/character data, hi-res screens — anything that must land at a fixed address.

A missing or non-program file gives ?FILE NOT FOUND. SAVE over an existing name fails on disk (FILE EXISTS) — see SCRATCH below.

How do I show a disk directory?

The directory is itself a (pseudo) PROGRAM file named $:

LOAD "$",8           (then)   LIST

LOAD"$",8 reads the directory into memory as if it were a BASIC program, overwriting whatever program you had; LIST then displays it. Each "line number" is the file's block count; the text is the filename and type. To peek at a subset use a pattern, e.g. LOAD"$0:A*",8 then LIST. To list the directory without clobbering your program, read it through a channel with GET#:

10 OPEN 1,8,0,"$"
20 GET#1,A$,B$           : REM skip load address
30 GET#1,A$,B$           : REM line-link / block low/high
40 ...                    : REM read & print each entry, then CLOSE 1

(The full byte-walk is fiddly; the simple LOAD"$",8 : LIST is what most users want.)

The command channel (channel 15) — DOS commands

Open secondary address 15 to talk to the drive's DOS. Send commands with PRINT#; read results/errors with INPUT#.

OPEN 15,8,15                 : REM open the command channel
PRINT#15,"<command>"
INPUT#15,EN,EM$,ET,ES        : REM read error channel: number, message, track, sector
CLOSE 15

Standard 1541 DOS commands (sent as the PRINT# string):

Command	String	Effect
NEW (format)	"N0:label,id"	format the disk: name label, 2-char id. "N0:label" (no id) does a quick clear of an already-formatted disk
SCRATCH (delete)	"S0:name"	delete file(s); pattern allowed (S0:TEMP*)
RENAME	"R0:new=old"	rename old to new
COPY	"C0:new=0:old"	copy a file on the same disk
INITIALIZE	"I0"	re-read the BAM / reset the drive
VALIDATE	"V0"	reclaim free blocks, fix the BAM (like a "collect")

The 0: is the drive number within the unit (always 0 on a single-drive 1541). You can also abbreviate the open: OPEN 15,8,15,"N0:GAMES,01" formats at OPEN time.

Reading the error/status channel

After any DOS operation, read channel 15 to find out what happened. A reset/OK status is 00, OK, 00, 00. The drive light blinking means an uncleared error.

10 OPEN 15,8,15
20 PRINT#15,"S0:OLDFILE"
30 INPUT#15,EN,EM$,ET,ES
40 PRINT EN;EM$;ET;ES        : REM e.g.  62 FILE NOT FOUND 00 00
50 CLOSE 15

EN = error number, EM$ = message text, ET/ES = track/sector. Reading the channel also clears the error and stops the blinking light.

Sequential data files

For your own data (not programs), use a data channel (sa 2–14) with a file type and mode in the name:

OPEN 2,8,2,"NAME,S,W"   : REM open SEQ file for Write
PRINT#2,"DATA";CHR$(13);"MORE"
CLOSE 2
OPEN 2,8,2,"NAME,S,R"   : REM re-open for Read
INPUT#2,A$
CLOSE 2

Separator pitfall (same as tape): PRINT# to disk needs RETURN (CHR$(13)) or comma between items, or INPUT# reads them back as one merged string. See c64-tape for the worked DOG/CAT/TREE example — the formatting rules are identical.

File types

Type	In name	Meaning
PRG	,P	program (BASIC or ML); the default for LOAD/SAVE
SEQ	,S	sequential data file (read start-to-end, like tape)
REL	,L / REL	relative file: fixed-length records, random access by record #
USR	,U	user file (rare; app-defined)

Relative and random files use a separate data channel and command channel; the PRG manual leaves the REL record protocol to the disk drive manual.

Quick answers

• "How do I list a disk directory?" LOAD"$",8 then LIST.
• "LOAD"NAME",8 vs ,8,1?" ,8 relocates to BASIC start; ,8,1 loads to the saved address (use for ML/data).
• "How do I delete a file?" OPEN 15,8,15: PRINT#15,"S0:NAME": CLOSE 15.
• "How do I format a disk?" OPEN 15,8,15,"N0:MYDISK,42": CLOSE 15.
• "Why is the drive light blinking?" An error is set — read channel 15 with INPUT#15,EN,EM$,ET,ES to see and clear it.

How to read the references

• references/disk-storage.md — the verbatim PRG Ch6 "Data Storage on Floppy Diskettes" text (sequential/relative/random files, the data+command channel concept) plus the disk-relevant slices of the LOAD and OPEN keyword entries (secondary-address rules, file type/mode syntax, error conditions). Read this for the exact wording on relocation, channels, and OPEN syntax.

Cross-links

• The general device/file model and the serial bus the drive sits on → c64-io
• KERNAL LOAD/SAVE routines (LOAD $FFD5, SAVE $FFD8, SETLFS, SETNAM) → c64-kernal
• Cassette storage and the shared PRINT#/INPUT# separator rules → c64-tape