A minivan full of magnetic tape is still fast
February 3, 2023
Y’all heard of the old Computer Science joke: “Never underestimate the bandwidth of a minivan full of magnetic tape”? I wonder if a van full of tape is still faster than broadband Internet these days.
Assuming a minivan has a cargo capacity of 4 m³ (140 ft³)…
A 1970s 9-track magnetic tape has a capacity of 1,360 Mb (170 MB) and has a volume of 30 cm×30 cm×1.5 cm = 1350 cm³. You can fit around 3000 reels in a minivan, for 4 Gb of data.
Normally, the bandwidth calculation would need to take into account how far the destination is—a destination twice as far would take twice as long, halving the bandwidth. Because we want to take latency out of the equation, we’ll assume we have a bumper-to-bumper traffic of minivans, so the data would only have to travel the length of one minivan before another minivan arrives.
Assuming a highway speed of 15 m/s (67 MPH) and a minivan length of 5 m, each vanload of bits would have to wait only 0.33 s before getting on the road, yielding a grand total bandwidth of…12 Gb/s!
Not bad for a highway full of bumper-to-bumper 9-track tapes in 5-meter-long minivans.
Modern tape backup is done on much higher bits-per-volume tape. An LTO-9 cartridge has a volume of 230 cm³ and a capacity of 144 Tb. Loaded with that tape, our modern minivan would have a bandwidth of an astounding 2.55 Pb/s, or about 213,000 times faster.
Never, indeed, underestimate the bandwidth of a minivan full of magnetic tape barreling down a highway.
Image generated by DiffusionBee. Prompt: “Computer magnetic tape reel mounted in a minivan on the highway abstract art” ↩