how can devices such as hard disks transfer data so much faster with much thinner cables than decades ago?

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I mean those wide, flat cables with many smaller cables inside. Now there’s just the very thin cables. Also USB for external disks.

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The wide flat cables that you may remember were PATA cables that worked by sending data in parallel.

Modern thinner cable like SATA, SAS, USB are alle serial (that is what the S stands for in all those acronyms)

With parallel connectors and cable if you want to send 8 bits, you send each bit in its own wire. You had 8 wires next to each other and each gets a bit send through it.

It is several people walking next to each other down the street.

Serial connectors send all the data down a wire in series. if you want to send 8 bits you send 8 bits one after the other down a single wire.

It is like several people walking down the street single file.

Intuitively you might think that the parallel way would faster and the serial way slower.

However it turns out getting the timing right in making sure that all the wires were in synch and stuff like that cost more time than just sending all the data down a single path.

This is why most modern connectors are some from of serial connectors. It works faster and better and it also saves a lot of space.

The data can be sent through the cable much more efficiently and quickly today.

Imagine you want to send drivers with packets to a big customer.

Earlier, you could only place one packet into one car, which had a constant speed while on the way. So you needed either more time, so one car would constantly drive back and forth to deliver everything or you sent more cars. That with the many cars would be that broad IDE cable.

Today, you have trucks that can fit a bunch of packets. Each truck isn’t much faster while driving. But where you needed multiple cars earlier, you need one truck now to deliver everything in the same (or similar) time. (SATA cable for example)

Also the storage facilities improved. Where earlier a couple slow hand-and-muscle operated pallet jacks were used, now they use forklifts, so to speak.

But I am sure there are also other points that I didn’t think of.

One improvement is the use of ‘twisted pairs’ of wires in the cable these are tightly wound to each other. USB and Ethernet uses this. This allows the signal to switch between 1 and 0 faster by providing a more reliable connection that is less prone to error.

The reliability is because the signal can be compared between the two wires – rather than a fixed value. E.g if the first wire is a higher voltage than the second then we can count it was a ‘1’ if the second wire is higher then it’s a ‘0’. This allows a lower voltage to be used since even if there was 2V of interference induced – both wires would be affected in the same way so they would still read as the correct value when comparing them. It can also be faster to switch a lower voltage on and off.