Granted, I wasn‘t aware. But unless you also have to tell CP/M how many cylinders and/or tracks you want to allocate for your „file“ upfront, and how large the

Granted, I wasn‘t aware. But unless you also have to tell CP/M how many cylinders and/or tracks you want to allocate for your „file“ upfront, and how large the (single!) extent should be should that allocation be exceeded, as well as having to separately enter your file into a catalogue (instead of every file on disk implying at least one directory entry, multiple for filesystems that support hard links), then CP/M and MS-DOS files are still very similar to each other. Also, it sounds to me like those 128 byte records were still very much sequential. That is, 128 bytes may have been the smallest unit that you can extend a file by, but after that it‘s still a consecutive stream of bytes. (Happy to get told that I’m wrong.) With MVS, the „files“ can be fundamentally indexed by record number, or even by key, and it will even be organized like that by the disk hardware itself.