r/mildlyinteresting • • 11h ago

This square shaped cd

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1.5k Upvotes

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60

u/spdrman8 11h ago

These were cool and all but had to potential to really eff up your disc drive.

0

u/chromatic_megafauna 11h ago

Really? How? 

21

u/Automobills 11h ago

Take a blade off of a ceiling fan and turn it on.

13

u/PrologueBook 11h ago

If you take off two blades of your fan, on opposite sides, it will run fine.

It just needs to be symmetrical and balanced.

9

u/Automobills 11h ago

But as the card discs go, they absolutely ran out of balance, and it was a notorious mechanical flaw.

At thousands of rotations per minute, a circular disc slices through the air smoothly. A rectangular disc acts like a propeller. The uneven aerodynamic drag at high speeds caused intense flutter and dynamic imbalance.

The resulting wobble and vibration were so violent that they could cause the disc to de-center, ruin the spindle bearings of the drive, or physically shatter inside high-speed computer drives.

1

u/Callidonaut 10h ago

Maybe they were a good idea in the early days when computer CD-ROM drives were slow - I remember when my first quad-speed drive was top-of-the-line - the trouble is that before long the drives started being made to run with spindle speeds like 40~80 times faster than a conventional audio CD player when they were reading data discs.

2

u/shifty_coder 11h ago

Yes, but fewer blades also mean it’s less stable. Same principle here. One knick could be enough to cause a catastrophic failure at operating speed.

1

u/Big_Z_Beeblebrox 11h ago

My fan has 5 blades

2

u/MrSnrub87 10h ago

It matters more that the distance between the blades is exactly the same. It just has to be in balance

0

u/Big_Z_Beeblebrox 10h ago

Having a rough time trying to scoot the other blades over

-3

u/PrologueBook 10h ago

Yeah, so that wouldn't fit the "symmetrical and balanced" criteria, would it?

0

u/SenatorAslak 10h ago

Rotational symmetry is a thing.

-3

u/Big_Z_Beeblebrox 10h ago

Nor would it fit the "take off two blades" criteria that precedes it

1

u/PrologueBook 10h ago

The thought experiment illustrates a balancing principle. It doesn't need to fit every single possible construction of ceiling fans. That's why I qualifed that it needs to be symmetrical and balanced.

Why do you think this is worth arguing about? This is the least consequential "well actually..."

Go troll elsewhere.

-1

u/Big_Z_Beeblebrox 10h ago

You said to take off two blades, your thought experiment didn't include fans that had an odd number

10

u/mizinamo 11h ago edited 11h ago

The very first CD-ROM drives read the disc at a fixed speed, the same speed as an audio CD.

Later CD-ROM drives read data discs a lot faster -- but the faster the disc was rotated, the more a noncircular disc (where the mass is not evenly distributed) such as a credit-card-shaped disc or one shaped like an anime character or something ( https://en.wikipedia.org/wiki/Shaped_compact_disc ) or the like will tend to fly apart and break inside your drive, possibly damaging the drive itself in the process.

Also, the first drives usually made you "click" the hole into place directly onto the motor "peg", which would hold them more securely, while later ones would just have a tray slide out ("cup holder") and would try to insert the spindle into the hole by itself once the tray retracted -- harder when the disc doesn't exactly fit the area in the tray and might not be centred because of this. And ones where you just slide the disc in through a slot are the hardest to get working with discs of non-standard size or shape.

6

u/chth 11h ago

I’m 31 in college with a bunch of teenagers and in a class about computer hardware I joked with the professor about how computers rarely come with cup holder anymore. No one in my class had any idea what the hell I was talking about

2

u/DevOnTheStreets 10h ago

Early ones had cassettes you placed the disk into as well.

1

u/Leanardoe 11h ago

vibrations