Why are there so many data wipe/erase methods for HDD?

It doesn't really matter its purpose, what matters are my questions:

1. I was thinking, if you fill all the HDD with 0's, how in heavens one person could recover data from there?
What am I missing?

OK, I understand the "how" if the tracks are way wider than the head (but are they in modern 500GB HDDs with high density?), but then, I asked the next question...

2. Why the head was/is smaller?

They did know that HDDs would store very sensible information, but even it they wouldn't, why would you make such a poor design in terms of correct deletion of data, noise in tracks, etc...?

Didn't they thought about making a bigger head that overlaps a little bit tracks that are touching each other, so when you command "delete this", the mechanism actually deletes it without any doubts?

The core question is why they allowed all of this "in between tracks old data" to happen if apparently is very easy to resolve. I'm looking for someone to tell me "no, you got this wrong about how it works", or "no, if you simply make the head bigger then this and that".

rambomhtri said:

It doesn't really matter its purpose, what matters are my questions:

1. I was thinking, if you fill all the HDD with 0's, how in heavens one person could recover data from there?
What am I missing?

OK, I understand the "how" if the tracks are way wider than the head (but are they in modern 500GB HDDs with high density?), but then, I asked the next question...

2. Why the head was/is smaller?

They did know that HDDs would store very sensible information, but even it they wouldn't, why would you make such a poor design in terms of correct deletion of data, noise in tracks, etc...?

Didn't they thought about making a bigger head that overlaps a little bit tracks that are touching each other, so when you command "delete this", the mechanism actually deletes it without any doubts?

The core question is why they allowed all of this "in between tracks old data" to happen if apparently is very easy to resolve. I'm looking for someone to tell me "no, you got this wrong about how it works", or "no, if you simply make the head bigger then this and that".

A HDD stores a permanent magnetic field on the disk surface. This field is interpreted as 1 or 0. But this field doesn't need to be 0 and 100% to be interpreted as 0 or 1.
For example, It can be 0 to 50% to be interpreted as 0 and it can be 50 to 100% to be interpreted as 1.
When you clean the disk with 0 you may find some bits with bigger fields than others. Same thing when you clean with 1.
Let's say you have a 0 then you store a 1. The field will be bigger than 50% but less than 100%. So you can assume you had a previous 0 on it.
If you find a 1 and the field is high, you can assume you had a previous 1 on it.
Low fields (0) means that the previous was a 0. Medium low (0) means that the previous was a 1.
High fields (1) means that the previous was a 1. Medium High (1) means that the previous was a 0.

Of course this kind of recovery can't be done with an ordinary disk controller or computer.
For normal disposal, only do a full format or use a software to fill it with 0 or with 1 or more effective with random 0 and 1

Macboatmaster said:

OK
as you say, it does not really matter - what the purpose of the thread is.
However I will leave it with other members, as IMHO the points questioned have been more than adequately covered and as I see the situation unless we know the reason for the posted questions, we are simply going to go round in circles.

You misunderstood what I meant. I said that it doesn't matter at all if I want to know the answers to my questions because I want to wipe my HDD's or because I want to know technical stuff, really, it doesn't matter, the answers will be the exact same thing.

How are you going to go around circles answering a direct simple technical question about data erasing of HDDs???

Anyways, megahertz answered my question in his last intervention.