The video recorder page of The Way Things Work, showing the tilted video head drum. A large outline arrow curves around the base of the drum pointing to the left, while the tape crosses the front of the drum travelling to the right.
The bit that causes the confusion. The tape crosses the near face of the drum travelling left to right. The big outline arrow beneath the drum — the rotation indicator — points left. Follow the tape back to the erase head and the mismatch is right there. Illustration © David Macaulay, from The Way Things Work (Houghton Mifflin, 1988), p.260. Reproduced in part for the purpose of criticism and review.

That spread is page 260 in the 1988 first edition, and page 244 of The New Way Things Work (1998), where the same drawing is reprinted unchanged. If you got here by searching for something like the way things work video recorder correction, or way things work head drum wrong direction — this is the page you were after.

There is no published errata sheet for the book, and as far as we can find, nobody has written this one down before — so here it is.

The short answer

In a VHS machine:

  • The head drum rotates counter-clockwise viewed from above.
  • The tape travels left to right viewed from the front.
  • The tape wraps the face of the drum nearest the cassette.

Put those together and you get the thing that trips people up: where the head touches the tape, the drum and the tape are moving the same way. The drum runs with the tape, not against it.

Both seen from above — tape runs left to right

Correct head drum rotation Seen from above, the tape runs left to right across the near face of the drum and the drum rotation arrow points the same way. drum Same way — correct how a real VHS deck runs Reversed head drum rotation The same view, but the drum rotation arrow points the opposite way to the tape. This is what the published diagram shows. drum Opposite — reversed what the drawing shows
The whole difference in one picture. The tape direction is identical in both; only the rotation arrow changes.

Why that feels wrong

The natural intuition is that you would spin the drum against the tape, so the two speeds add up and you get a faster recording for free. It is a reasonable thought, and it is not how it works — because the tape contributes well under one per cent of the head-to-tape speed. The head is crossing the tape at nearly 21 km/h; the tape is ambling along at about 3 cm per second. Nobody was ever going to design a format around that difference.

So the direction was never really a choice. It falls out of the mechanics — where the reels sit, which face of the drum the tape is pulled around — and once the format existed it was frozen into the standard, because a tape recorded in Osaka has to play in Adelaide.

Check any diagram in three steps

  1. Find the tape’s direction. Look for the supply and take-up reels, or find the erase head — the tape always passes it before the drum, because the old recording has to be wiped before the new one is written.
  2. Work out which face of the drum the tape wraps. It is the side facing the cassette, towards the front of the machine — nearest you in most drawings.
  3. Compare the arrows at that face. They should point the same way. If the rotation arrow opposes the tape, the diagram has it backwards.

About the book

None of this is a knock on The Way Things Work. It has been my go-to reference for about thirty years — whenever I want to know how something actually works, rather than a summary of it, that is the book I reach for, and I still take it off the shelf regularly. Macaulay draws a machine the way a good teacher explains one: he shows you the part that matters, at the angle where you can see why it matters. Several hundred spreads of that, done with extraordinary care.

This is one arrow on one page. It is also genuinely hard to spot — invisible unless you deliberately trace the tape and hold it against the rotation arrow, which is a strange thing to do unless something has already made you suspicious. The people who would catch it instantly are VCR service technicians, and they were not who the book was written for.

For the record: the spread is page 260 in the 1988 first edition, reprinted unchanged as page 244 of The New Way Things Work in 1998. The 2016 revision, The Way Things Work Now, dropped the video recorder entirely — the format had gone — so the arrow was never corrected so much as retired along with the technology it described. We still recommend the book without hesitation.

Common questions

Is the video recorder diagram in The Way Things Work wrong?
In this one detail, yes. The rotation arrow shows the head drum turning against the tape, when a real VHS drum turns with it. The spread is p.260 in the 1988 first edition and p.244 of The New Way Things Work (1998), reprinted unchanged, and the text states the mechanism shown is VHS. There is no published errata sheet for the book, and the 2016 revision dropped the spread entirely — so nothing in print today carries it.
Which way does a VHS head drum rotate?
Counter-clockwise viewed from above the machine. Combined with tape running left to right and wrapping the drum face nearest the cassette, that means the drum surface and the tape move the same way where they touch.
Why not spin the drum against the tape for more speed?
Because there is almost nothing to gain — the tape contributes well under one per cent of the head-to-tape speed. The direction is set by the mechanical layout and then fixed by the format standard, so that tapes play on any machine.
Why is there a spinning drum at all?
Bandwidth. Tape only records high frequencies if head and tape move past each other quickly, and video needs far more of them than audio. A fixed head would mean the tape itself flying past at metres per second. Spinning a tilted drum instead lets the head write long diagonal stripes across tape that is barely moving.

If you got here because you were staring at that page thinking you must be missing something — you weren’t. Trust the trace.

Keep learning

Storage & media How a CD stores data Pits, lands, and the error-correcting maths that survives a scratch. Data & encoding How a computer knows a file isn’t broken Parity, checksums, hashes and ECC — spotting damage before it spreads. Learn All lessons Plain-English explanations of the fundamentals that don’t go out of date.