.SCL File Format

Introduction

An SCL file is a compact copy of the files on a TR-DOS disk: it keeps the descriptors and the files’ sectors and leaves out the empty disk, so it is much smaller than a TRD image. ZX Spectrum emulators read it as a disk (they lay the files out on a blank TR-DOS disk), and it is a common way to share Spectrum clone software.

Structure

The 8 bytes “SINCLAIR”, a byte with the number of files, one 14-byte descriptor for each file, the files’ sectors, and a 4-byte checksum. See Header, descriptors and checksum.

In the explorer

Drop a .scl file on the explorer to see the tree (header, every descriptor with its fields, every file’s data, the checksum), the list of files (name, type, load address, length, sectors), the Z80 code of every CODE file disassembled at its load address, every file to open as bytes, and the problems found (wrong signature, a file count above 128, a length bigger than its sectors, a file cut short, extra bytes, a checksum that differs).

Not described

Known, not yet covered

• Viewer: the archive is not converted to a TRD image; BASIC files are not detokenised; the disassembly decodes every byte of a CODE file as an instruction.

Unknown

• Reference: the checksum’s byte order. Two sources (the Spectrum FAQ and a FlashFloppy issue) say the last 4 bytes are the sum of all the bytes before them; neither gives the byte order, so little-endian is our inference and a “differs” problem on a real file may mean big-endian.
• Viewer: no real SCL file is on this Mac and none was fetched; the reading is checked on built files only.

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