QIC standards

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QIC standards

This section summarises the QIC standards as far as Tapewyrm uses them, and the vendor structures that real backup software wrote on top of them. Each page gives the layout, cites the standard and section it comes from, and notes where Tapewyrm departs from the standard or relies on bench observation.

The standards themselves are in docs/qic-standards/; the QIC standards library lists every PDF.

The layer stack

A floppy tape is read through a stack of formats. Each layer consumes the one below it, and each is handled by one part of the code.

Layer Standard What it defines Implemented in
Command interface QIC-117 Pulse-count commands on Step, report bits on Track Zero, cue pulses on Index. Firmware src/qic/qic.c; tapewyrm.qic117 (commands, drive, profiles); tapewyrm_archive.qic117 (report decoders)
Recording format QIC-80-MC, QIC-3010/3020 Serpentine tracks, 32-sector segments, MFM, sector IDs, the coordinate algebra. tapewyrm.codec.gwstream, gwpll, mfm (flux to sectors); qiclib.merge, qiclib.place, qiclib.geometry
Error correction ECC Reed-Solomon over GF(256), 3 parity sectors per segment, erasure decoding. qiclib.segment, qiclib.rs
Header segment Header and bad-sector map Format parameter record, geometry, the bad-sector map. qiclib.header
Volume table Volume table 128-byte VTBL entries: one per backup volume. qiclib.volume.table, qiclib.volume.profile
Compression QIC-122 Stac LZS frames inside QIC-113 compression extents. qiclib.volume.qic122, qiclib.extract
File sets QIC-113 Directory and data sections: the files themselves. qiclib.volume.qic113, qiclib.volume.qic113ext, qiclib.volume.fileset
Vendor layouts Vendor formats What specific backup programs wrote in the parts the standards leave open. Volume profiles in qiclib/volume/profiles/

QIC-122 sits below QIC-113 in the read order: a compressed volume is decompressed first, then its directory and data sections are parsed. The standards describe it the other way round because QIC-113 ยง9 defines the extents that carry the QIC-122 stream.

Where the tools cut the stack

drive --QIC-117--> tw dump ----> TWRF   (flux, one file per track pass)
                   tw convert -> TWTI   (placed, BSM-applied, RS-corrected segments)
                   qicsilver extract -> TWVL (one volume, decompressed, with holes)
                   qicsilver tar ----> tar  (files)
  • tw dump captures flux and stores it unchanged. See TWS-1 TWRF.
  • tw convert does the recording, ECC and header layers once, and writes a logical tape image. See TWS-2 TWTI/TWTZ.
  • qicsilver extract reads the volume table through a volume profile and decompresses the volume. See TWS-3 TWVL.
  • qicsilver tar parses the file set and writes a tar with a damage report.

Everything above the TWTI is offline and needs no hardware, so a tape is decoded once and can be re-extracted as profiles improve.

Conventions on these pages

  • Offsets are decimal, with hex in parentheses where the standard uses hex.
  • Multi-byte fields are little-endian unless a page says otherwise.
  • "Word" is 2 bytes, "doubleword" 4, "quadword" 8, as in the standards.
  • "Bench" marks something observed on real tapes or drives and not stated by a standard.

See also