| Feature | IDX | NumPy .npy | HDF5 | TFRecord | |---------|-----|--------------|------|----------| | Header size | 4 + 4×D bytes | ~128 bytes + metadata | Variable | Variable | | Data compression | No | Optional (via NPZ) | Yes (filters) | Yes | | Random access | Manual stride calc | Yes | Yes | No (sequential) | | Cross-platform | Yes (big-endian) | Yes (little-endian fixed) | Yes | Yes | | Metadata support | None | Dict in header | Full attributes | Per-example | | Streaming read | Yes | Yes | Yes | Yes | | Max dimensions | Up to 255 (byte) | Unlimited (via pickle) | Unlimited | N/A | | Standard library support | Custom code needed | NumPy | h5py | TensorFlow |
A standard IDX file contains:
No metadata, compression, or checksums are included by default, making it both extremely fast to parse and brittle in the absence of external documentation. idx file
This report details the format’s byte-level specification, examines its historical and contemporary applications, provides implementation examples, analyzes performance characteristics, and discusses its limitations relative to modern formats like HDF5 or NPY. | Feature | IDX | NumPy