Hard disk with two or more read / write heads, why don't they exist?

In Brazil, more than 95% of home computers still use a mechanical hard disk, that hard disk based on magnetic technology on a rotating plate where it has a single arm for reading and writing data.

For years, companies that produce hard drives have worked to increase storage capacity, and improve their actual performance by increasing the disk's spin speed and reading / writing in increasingly smaller spaces.

But, for what reason, instead of making improvements in space and speed, you simply did not put several reading arms inside to increase performance?

To get these answers, we have information from Seagate, to understand that the reason for this is not as simple as it seems, and that this has existed before.

Hard drives in the 60s, were very different from what we currently see. The hard drives of that time, in general, had 10, 12 or more reading arms, independent for each iron ferrite hard plate, recording in a magnetic way in the circular and easily accessible areas (unlike the magnetic tape, which to access an area, the tape needed to be rolled).

But shortly thereafter, the discs started using only 1 fixed attenuator, with several heads, and simpler prototypes started to be created in this way.

So most hard drives started to adopt a single attenuator, even though it actually has 2 heads or more (one for each plate), there were no 2 separate attenuators, working independently, at least not until the prototype of the company Conner Peripherals, which held a patent for a hard disk design with 2 reading arms.

Prototype of 2 reading arms from the company Conner Peripherals.

Basically, companies of the time, simply could not make a hard disk with 2 reading arms or more, due to this patent, but the reason the company itself did not make discs and use the patent were others, apparently not but a probable financial cause.

After a certain time, Seagate bought the company Conner Peripherals, and thus took the patent for discs with 2 arms, and made the first hard disk with 2 reading arms, on a disk with 10 MB of storage, but the arms did not they were independent to work on the entire record, one arm worked only on part of the record, from the beginning to the middle, and the other from the middle to the end, and never together in the same area.

The arm moved straight, just like optical drive drives, using a servo motor, to move the arm forward or back, not as we currently see in a circular shape.

Seagate 10 MB capacity disk with 2 read / write arms.

After this, Seagate came to create a 2GB storage disk with 2 arms in the current model that we know, cyclically, promising twice the data transfer, but with the increase in space, Seagate stopped producing these disks.

The main factor was the cost of the discs, followed by an increase in the number of components, an increase in the weight of the material, and the advantages were minimal, apart from discs with 2 reading arms, they would make discs bigger and hotter, and also with electrical consumption bigger.

Another detail also pointed out is that no read / write heads are the same. They adapt to the disk they work on, and can increase or decrease in size, or write physically in different places, and 2 reading arms, with 2 heads reading the same area, could bring inaccurate and wrong results.

It is as if the read and write head were unique to the media, and another could hinder the process and even cause a greater loss of data than actually increase performance. For this reason, there is only 1 single read head per side of the disc.

Seagate also states that, although today, it is possible to develop disks with 2 or more arms, it is not a viable business solution, as the current focus is on the development of solid state disks, and on increasing their storage capacity. .

See more documents about the patent for the 2-arm disc on the same disc: