.TZX

Introduction

A TZX file is a copy of a cassette tape for the Sinclair ZX Spectrum. Most Spectrum software was sold on tape, and TZX is the format used to preserve it. Emulators play a TZX file as if it were the tape.

The simpler TAP format only stores the bytes of standard tape blocks. TZX also describes the timing of the sound itself: the lengths of pilot tones, sync pulses and bits. That lets it hold the turbo loaders and copy protection that many commercial games used. Amstrad CPC tapes use the same format with the extension .cdt.

Structure

The file starts with a 10-byte header: the text ZXTape!, the byte 1A, then the major and minor version numbers. Blocks follow until the end of the file. Each block starts with an ID byte that says what it is and how long it is. Common blocks are 10 for a standard speed data block, as the Spectrum’s own loader writes it, 11 for a turbo speed block with its own timings, 12 for a pure tone, 13 for a sequence of pulses, 14 for pure data, 20 for a pause, 21 and 22 to start and end a group, and 30 and 32 for a text description and archive information such as title and publisher.

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