General Things About HDD's

[QAsker]

I wanted to know how many types of hdd's are there ? What is the diff. Between them ? And are all types of hdd compatible with all mb's ?

 

[canadianvice]

I wanted to know how many types of hdd's are there ? What is the diff. Between them ? And are all types of hdd compatible with all mb's ?

You may wish to narrow your question a bit.
As it stands, there's mostly 2 major forms of permanent hard disk memory: SSDs (flash NAND cell based), and HDD's (magnetic field on disk based).

You can also buy ramdisks, but I don't believe those are used for permanent memory often as they're massively expensive and there's no way to preserve data through power loss.

In theory, any of SSD or HDD should work just fine with a motherboard, as long as the interface used for the connection is the same. Ie: IDE will not work with a SATA based hard drive, and that sort of thing. SATA is more or less totally backwards compatible, but you will see a speed reduction. It's similar to USB in that regard.

Differences?
SSDs use flash memory which is much, much faster, especially for random access. However, it suffers from density issues (only so much in so small a space) and at present is at a premium cost.

Hard disks use spinning magnetic platters that have a small reader head to go over them, like an old record player. They are much cheaper to purchase, but a fair bit slower and less durable due to moving parts.

Now, to use the parable of a block of houses and a mailman to explain how file access happens on both.
Say we have a file (a bunch of houses, since files are pieces of data) and a mailman who has to get mail or retrieve mail from each house on the block. Say there are 10 houses.

Because house 1 could decide to expand (you add more data to a file) the city zoning official has to allow some space for it to get bigger. This leads to fragmented files, where the house may not all be on the same lot.

On a mechanical hard drive, (HDD, is the term I'll use - spinning disks) houses are a bloody mess. They're in random order. (consider the houses to be files or more accurately, parts of a single file to be retrieved).

The poor mailperson, to get the mail to the entire houses, has to walk up and down the block several times, stopping at whatever order may be easiest. As you may have assumed, if each house was in perfect order, it would be the most efficient. He'd never cover repeat ground moving back and forth. This is why mechanical drives are a lot slower - files aren't always contiguous, and so it has to spin back and forth, making a lot of the movement in 3D space redundant. (Say, from houses 1-6-4-9-2) You see the need to cover repeat ground?

By comparison, an SSD has a similar situation for the organization of the houses, but the mailperson can teleport. An address for the start and parts of a file is sent to the controller on the drive, and it basically goes straight to the part and pulls it. Naturally, if there's a lot of this back and forth, teleporting is much faster, since no repeat ground is covered.

If the houses are arrayed in order and so is his mail, you can see there wouldn't be a huge advantage from one over the other. Sequential files perform well on both drives.

HOWEVER
If the houses are in random order and his mail is too - if he can just teleport to each house, he saves the time it'd take to repeat the route back to the house. This is random access. HDD's suck at it, but since SSD's go anywhere and have no physical limitations to getting there, like navigating a disk through rotating it, they're much faster at it.

I hope this helps explain, or I may have just written something massively confusing. The performance you get on these drives depends on their uses too - music and text are always sequential, though they may still be split up if other files are in the way (say you make two files, and then expand the first afterword, it would look like 1-2-1) but the disk only needs to turn one way, and so it's much faster for a HDD.

Random access would be more akin to loading game assets. You don't know if the game needs to load a jet or a SUV in a specific order, if say, you're playing Battlefield. Your HDD would have to spin back and forward depending on where the parts of the files were located. Rather, forward, but it has to cover repeat ground.

An SSD, on the other hand, gets an address to the files for a jet and an SUV and goes straight to them, no turning or lag for 3D motion of a disk. Hence why it performs much better.

To clarify:
- When I say address, I refer to the start of a file (say, sector 200302 for file f.txt) that is stored in something called the Filesystem Table. This is what the "format" of a drive is. FAT32 has a database structured in a particular way listing the start address of every file, as an example. This is why drives never have the same space listed on the package, space has to be used to track this information (it's done via the controller, so you never see this).

- Controller: This is basic software with a small processing capability on the drive that decides how best to access files and where to put them. It knows where there's free storage spaces, what sectors (a unit of storage on a drive) are working, which ones are full, and which ones are non-functional. CHKDSK refers to these when it does its test to see if the drive is in good repair.

- Random access: This is pulling data or writing it in a random order. This is common with things that need dynamic assets like games. Not everything that shows up will come in the same, fixed order each time.

- Sequential access: Files that are like books. From left to right, and you will always have the same order of data. IE: a movie. You never start a movie with the credits, do you? It's always the film in a particular order, then the credits.

- Flash NAND memory: There are multiple varieties of this kind of memory, NAND being only one of them and the most common for SSD's. This memory works on the principles of logic gates (AND, OR, XOR, etc.) combined with electric charges stored in a cell (sectors for HDD's), to hold data without losing it when power is lost.

 

[QAsker]

Thanks A Lot