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Mr. Pedantic

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#1 9 years ago

Just out of personal interest, I've been wondering, how do hard drives store and read data? How is that different to the method of doing the same thing on a CD? A floppy? A flash drive? An SSD drive? An SD card? And the question that sort of got me really thinking about this, why is data storage for SSD's so expensive?




jjz-

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#2 9 years ago

Data storage for SSDs is so expensive because they use NAND (generally)-flash memory. This type of memory is expensive to produce in high capacity.

Harddrives store and read data through the magnetic material on the platters. The magnetic material can be magnetised and demagnetised through the disk head.

A CD-ROM is read using a laser that detects whether or not the laser beam is reflected off the disk. Using these findings, the data is reproduced.(1s or 0s). A indentation in the CD-ROM is created by a more powerful laser.

Flash drives use (generally) NAND memory as well.

Floppy drives use magnetism the same as harddrives; however, in much smaller capacity.

SD card is just another type of flash. It uses nand, as well.




Junk angel

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#3 9 years ago

I'm just curious about one thing. Don't SSD drives get corrupted very soon. Most of all, when they get fragmented?

Wasn't there just so many write cycles (far below those of conventional HDDs) before they ceased to work.

The least had CDRW's though.




jjz-

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#4 9 years ago

SSDs have a MTBF (Mean time between failure) that is generally HIGHER than general harddrives. They generally last *longer*.

Files, of course, can get fragmented in an SSD; however, there is no real performance loss. The reason fragmentation is bad in a standard hard drive is because the hard drive has to keep seeking the parts of the fragmented file, which takes many milliseconds. SSD "seek" is pretty much instant, on the order of microseconds. Thus, fragmentation is not a performance detriment to an SSD and that is one less piece of software (if you use something besides the built in windows defragmenter, which you really should) you need on your computer.




Bs|Archaon

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#5 9 years ago
jjz-;4678025SSDs have a MTBF (Mean time between failure) that is generally HIGHER than general harddrives. They generally last *longer*.

Aye. People often dwell on the fact that an SSD is expected to die after a certain amount of use, without realising that HDDs are far more likely to malfunction and die in some kind of horrible way. Even when they're only a few months old a HDD is liable to pack in for no real reason. The difference is that with a SSD you have a ticking clock; with an HDD it just happens.

In reality the MTBF on a SSD is no different to a HDD company giving you a warranty for 3 years or whatever. Either can die before the MTBF/warranty expires. Either can last for years after the MTBF/warranty expires. Just depends how lucky you are.




Mr. Pedantic

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#6 9 years ago
Aye. People often dwell on the fact that an SSD is expected to die after a certain amount of use, without realising that HDDs are far more likely to malfunction and die in some kind of horrible way. The difference is that with a HDD you don't have a ticking clock - it just happens.

Well, I have four HDDs on my computer which have, on average, been in use for about six years each. And none of them have failed. So I don't know if its only down to luck, but also maybe other factors too.

Harddrives store and read data through the magnetic material on the platters. The magnetic material can be magnetised and demagnetised through the disk head.

So when its magnetized its aligned one specific way and when its not it's just random? Or are there different ways the head can magnetize the material?

A CD-ROM is read using a laser that detects whether or not the laser beam is reflected off the disk. Using these findings, the data is reproduced.(1s or 0s). A indentation in the CD-ROM is created by a more powerful laser.

What about a rewritable CD?

And what exactly is flash memory?




jjz-

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#7 9 years ago

Hmm, I do not believe there are different ways the head can magnetize the material. It simply magnetizes it to represent a "1" and demagnetizes to represent a "0". The head can sense the magnetic field (and of course, absence of one), and thus data can be reassembled.

As for a rewritable CD, it just melts the indented areas and then dries them back to their original state.

Well, there are many types of "memory", both volatile (erased on lack of power) and non-volatile (stays even without power).

Flash-nand memory is basically "programmable" memory. It uses a series of NAND gates (Complement-AND, meaning 1 && 1 returns false instead of true) to store data in the form of 1s and 0s. It would take me forever to explain how it works from the lowest levels of abstraction... Basically, all the gates start as open so all blocks of data (places where 1 or 0 can be set) are at 1. This represents null data (instead of the usual 0s representing null. Remember we are dealign with complements). Electrons can be forced out of certain areas and then gates can be closed, which will set the value to 0. This can be doen for each block, thus making a string of 1s and 0s, representing your data.




C38368

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#8 9 years ago

As of about two years ago, at least, early death of SSD drives was a major problem. Not due to mechanical failure (the usual cause of magnetic drive failure) but because the technologies in use had a markedly limited number of bit flips that could be sustained before the silicon failed--we're talking months for a home user.

Obviously, at that rate of degradation SSDs were not commercially viable. Given the fact that they are reasonably available these days, I'd imagine that the issue has either been fixed, or reduced to the point of being irrelevant.




jjz-

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#9 9 years ago

Yes, it has. Modern SSDs now have between 700 thousand hours and 2 million hours MTBF. This is generally higher than a harddrive, or par with it.




C38368

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#10 9 years ago

On par. Most mechanical drives boast a MTBF in excess of 1 million hours now.




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