These are disk- and tape images files for the Commodore 64 and computers using the same floppy drives and disk formats, like the VIC-20, or the Commodore 128.
D64 are single-sided 5.25" disk images ("1541 images" for the Commodore 64), sometimes also called D41.
D71 are double-sided 5.25" disk images ("1571 images")
D81 are double-sided 3.5" disk images ...
The .z80 format comes from the Z80 emulator by Gerton Lunter. He released some documentation about the file formats used in it, and regarding offsets 11 and 12, this is what the manual says:
The old .Z80 snapshot format (for version 1.45 and below) looks like
Offset Length Description
0 1 A register
About the R register on a real Z80:
But is the 8th bit actually used?
Yes, it's freely available and won't be touched by any instruction except loading R
Is its behaviour undocumented or can it only be altered by loading it with a value from the accumulator
It's well documented and can be used like assumed. When loaded all 8 bits from A are stored in R - ...
Since I've been writing code to interact with various systems' disk image formats over the past few weeks I'd like to add a little more information that's not in the current answers.
Disk images and tape images are usually of a few different types and subtypes. I'm using my own terminology here so forgive me if there is standard terminology I'm not yet aware ...
I once wrote a program for this sort of situation: DSKREAD. It runs on a +3 and archives entire disks to tape. You could record the audio, convert to a .TAP file, and then load the .TAP in a +3 emulator to recreate .DSK images containing the original files.
As far as I know, no-one's tested DSKREAD on a real +3, so I've no idea whether it would actually ...
With Vice, you can wait until the uncompressed, actual, application code has started execution, then activate the built-in ML Monitor. You will thus pause execution at wherever the Program Counter happens to be, most likely waiting for the first user input to the application.
Dump the stack to see the history of any subroutines that have been invoked. Going ...
I've made a couple of discoveries after a night's sleep.
The CoCo still reads the leader length from a RAM address, but its address is two bytes higher in memory than in the Dragon 32:
0199 ** THESE BYTES ARE MOVED DOWN FROM ROM
0200 *** INIT DESCRIPTION
0201 * VALUE
0202 008F CMPMID RMB 1 18 *PV 1200/2400 HERTZ PARTITION
0203 0090 CMP0 RMB 1 24 *PV UPPER ...