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C64 disks & images, explained
New to all this? Start here - what a D64 actually is, and how the C64 world uses it.
What is a D64 file?
A D64 is a digital copy of a Commodore 1541 floppy disk - a single file on your PC that holds everything the real 5.25-inch disk did: its directory and all its programs. It's always 174,848 bytes (about 170 KB), mirroring the 1541's 35 tracks. Think of it as the C64 world's equivalent of a disk in a box - an emulator or a piece of hardware treats it exactly like the physical floppy.
What's the difference between D64, D71, D81, D80, D82 and DNP?
They're images of different Commodore drives. D64 is the classic 1541 disk (170 KB). D71 is a double-sided 1571 (340 KB). D81 is the 3.5-inch 1581 (800 KB). D80 and D82 are the big PET/CBM 8050 and 8250 drives. DNP is a CMD “native partition” - a hard-disk-style container up to 16 MB, used by SD2IEC and CMD hardware. Retro Commander reads and writes all of them.
And G64, NIB, T64, TAP, PRG and CRT - what are those?
D64 stores a disk's decoded sectors; G64 and NIB instead keep the raw, low-level track data, which is what you need to preserve copy-protected disks faithfully. PRG is a single program, not a disk - one file with a two-byte load address. T64 is a container that only holds PRG files (a relic of an old emulator; despite the name it is not a real tape). TAP is a true Datassette tape recording. CRT is a cartridge image. Retro Commander focuses on the disk-image family: D64, D71, D81, D80, D82 and DNP.
How do I use a D64 with an emulator?
In an emulator such as VICE you “attach” the D64 to virtual drive 8, then on the C64 type LOAD"$",8 and press RETURN to list the directory, or LOAD"NAME",8 followed by RUN to start a program. Most emulators also offer a “smart attach / autostart” that does it in one step. Retro Commander prepares and edits the disks on your PC; the emulator runs them.
How do I use disk images with real hardware?
The cheapest route is an SD2IEC - a small device that pretends to be a 1541, so you drop D64/D81 files onto an SD card and mount them. For full fidelity there's the 1541 Ultimate, Ultimate-II+ and Ultimate-64, plus the Pi1541, which emulate the 1541 cycle-exactly and can run G64s and copy-protected images. Retro Commander connects directly to the Ultimate family over your network.
What are GCR, half-tracks and copy protection - and when do I care?
The 1541 wrote data as GCR, a magnetic encoding, and games often abused it with non-standard tracks, odd sync marks or “fat tracks” to stop copying. A plain D64 discards that low-level detail, so an original protected disk may not run from a D64 - for those you need a G64 (or a flux dump) that keeps the raw encoding. For everyday demos, tools and already-cracked games, D64 is perfectly fine.
Where do I find disk images legally?
Scene productions - demos, intros and music - are released for free by their authors on CSDb. Gamebase64 catalogues games, and the Internet Archive hosts large collections. New commercial titles come from homebrew publishers such as Protovision, RGCD and itch.io. Remember that many original games are still under copyright: stick to scene and homebrew releases, and anything explicitly shared by its makers.
How were these images made, and can I image my own disks?
Most images were “dumped” from real floppies. For ordinary disks, a 1541 with a transfer cable (X1541 or ZoomFloppy) plus software like OpenCBM does the job. For copy-protected or fragile disks, preservationists use flux-level hardware - KryoFlux, Greaseweazle, or a Pi1541/Ultimate - to capture the raw magnetics into G64 or flux files for archival.
Is a disk image a “ROM”? Will it run a game by itself?
No. A disk image is just storage - the equivalent of a floppy in a box. You still need a C64, real or emulated, to run what's on it, along with its built-in KERNAL and BASIC ROMs. Retro Commander manages the disks; the C64 - hardware or emulator - does the actual running.
Retro Commander specifics
Which devices are supported?
The Ultimate-64 and Ultimate-II+ from ultimate64.com, and the C64 Ultimate from commodore.net. All three share the same REST + FTP interface. The app doesn't gate behaviour on a specific firmware version, but very old firmwares may be missing some endpoints; keep yours reasonably current.
Does it run on Mac or Linux?
Not yet - but cross-platform support is now high on the roadmap for the next major release. Today it's a Windows-only WPF app, leaning on a few Windows-specific APIs (DWM dark titlebar, shell icon extraction), so a proper port is real work. There's no firm ETA: it depends on how this release lands with you and what the first pivot brings. And, candidly - more tips mean more days off from the day job, which means faster progress. ;-)
Where are settings stored?
In a settings/ folder next to the executable when the install location is writable (so the portable build stays portable). Otherwise it falls back to %APPDATA%\C64UManager\settings.json. The schema is versioned and migrates forward.
Can I connect to multiple Ultimate devices?
One at a time. Switch by changing the host in Settings - your last connection details remain saved between sessions.
Why does the app need .NET 10?
It's the current Microsoft desktop runtime for modern WPF features. The Lite build relies on the system runtime; the Portable build bundles a self-contained copy so it runs anywhere.
Is there telemetry?
Only aggregate operational metrics - never the contents of your files. The app reports counters such as session count, total usage minutes, and how many disk images you open or edit and files you transfer, so we can gauge load and prioritise features. There are no third-party analytics or advertising SDKs, no cross-site tracking cookies, and we never sell your data. Over the network the app talks only to your Ultimate device on the local network and our own licence server (sign-in, licence validation, device management, and these counters). See the Privacy Policy for the full list.
Is the source available?
No - Retro Commander is a closed-source project. The Windows builds on the Download page are the only distribution. Bug reports, feature ideas, and screenshots are still very welcome via the contact link on the donate page.
How do I report a bug?
Until a public issue tracker is up, send a short reproduction (what you did, what you expected, what happened) to the contact link on the donate page. Screenshots welcome.