# The Week In Storage: DNA Storage, Hitting The Magnetic Switches, Old HDDs Learn New Tricks

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#### JohnnyLucky

##### Illustrious
I like the weekly update. Keep it going.

#### humorific

##### Reputable
DNA memory + AI + genetic engineering + self replicating machines = ? Can you say skinjob?
Another point if you get the reference.

#### PaulAlcorn

##### Senior Editor
Editor

Nothing is worse than having an itch that you can never scratch!

#### Flame_Runner_Fast

##### Reputable
So...when will we have our artificial sheep singing our favorite songs in the near future?

#### mcfro

##### Commendable
Doesn't Western Digital already offer DNA storage on their Soylent Green line of hard drives?

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#### joex444

##### Distinguished
> The platter spins at roughly 75 miles per hour

Referring to hard drives, this "roughly" could be eliminated by noting that the platters are, as the name implies, circular and obey constant angular velocity (ie, revolutions per minute). Further, since the linear distance is the angular velocity times the circumference at that point, assuming 7200RPM (120 pi radians/s) we can deduce that 75MPH (1320in/s) implies that they are referring to a point at 1320/120pi = 3.5" away from the axis of rotation.

Further trouble is a typical 3.5" HDD has platters that are actually 3.74" so it would really be up to 80MPH -- or again, a constant 7200RPM.

This extremely dumb attempt to relate hard drive speeds, with an angular symmetry, to linear speeds is further mildly useful in explaining why transfer rates vary across the medium - why the beginning of the drive is able to read faster than the end. At the end, near 1.5" away from the axis of rotation the drive has a linear velocity of ~30MPH. Reading data at 30MPH is clearly slower than 75-80MPH, hence the drives read/write slower near the end of the drive and any attempt to measure an average speed is inherently flawed. Further, assuming the drive can actually only access data located between 1.5" and 3.5" the point which divides the drive into two equal areas of capacity is *not* 2.5" but 2.7" (since the first area would be related to 3.5^2 - 2.7^2 and the second area to 2.7^2 - 1.5^2 and we note that 3.5^2 - 2.7^2 = 2.7^2 - 1.5^2).