.SCP

Introduction

An SCP file is a flux image of a floppy disk, made by the SuperCard Pro disk reader. Instead of the decoded sectors, it records the magnetic flux transitions the drive head saw, as times between pulses. That is the lowest level a floppy can be copied at, so an SCP file keeps copy protection, unusual formats and damaged areas that sector images lose.

The format is not tied to one computer: the same file type holds Amiga, Commodore, Atari, Apple, PC and other disks. Other flux readers, such as Greaseweazle, also write it, and preservation projects use it as an archive format.

Structure

The file starts with a 16-byte header: the text SCP, a version byte, the disk type, the number of revolutions recorded per track, the first and last track numbers, flags, the width of the flux values, the heads recorded, the timing resolution and a checksum. A table of track offsets follows, one 4-byte entry per track.

Each track starts with TRK and the track number, then, for each revolution of the disk, the time the revolution took, the number of flux values and where they are. The flux values are 16-bit big-endian counts of a 25 nanosecond clock, by default; a value of zero means the gap was too long for 16 bits and the next value continues it.

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