| 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
