HDD

Hi folks,

After telling a few things about CPU and RAM let us present you today some basics about hard-disks and thus end the series of brief descriptions on how the key hardware components inside a computing device (computer, tablet, smartphone) are working.

The deliberate lie we’ve inserted in our previous article was about the French group Daft Punk being the inspiration source for the term « Random Access Memory« ; they didn’t originate this technical term of course.
On the contrary, the title of their album was inspired by the notorious name of this type of memory which they’ve « poetized » by  switching from the singular « memory » to the plural « memories », thus turning its resonance from tech to human.
But that said, let’s see how you’ll be doing with today’s hidden lie.

Everyone knows that a hard-disk is the thing that preserves information on long term and that data saved on it is kept even if after the computer is power-off, remaining available for any time unless it is being deleted or the disk suffers severe physical damages.

The hard-disk was invented in the 1950’s and its initial name, « fixed-disk » turned to the « hard-disk » name we are still using currently because the magnetic medium (that actually stores information) is placed on a hard (aluminium or glass) platter, as opposed to the magnetic-tapes of floppy-disks of those times, where the magnetic medium layed on flexible films made of plastic.
So in order to store as much information as possible and make it retrievable for reading/writing purposes in as little time as possible it had to be a ‘disk’ (to provide random access instead of sequential access as in magnetic-tapes) and it had to be ‘hard’ rather than flexible too, in order to allow a high-speed and heavy-duty electro-mechanical infrastructure to operate.
Of course, hard-disks were initially very expensive as innovation always comes at a price.
But when computer industry really took off, they got cheaper and cheaper while becoming more and more performant so today’s HDDs (Hard Disk Drives) are, by comparison, unbelievably cheap and performant having unbelievable small sizes too.

Basically, the hard disk consists of many platters with many reading heads.
Platters are the place where the real action happens: information is read from or written on their magnetic layer so they have to be polished, finished and uncontaminated to perfection.
This is why hard-disks are assembled in clean-rooms and the main part of any hard-disk is sealed: an unsealed HDD is a compromised one.
The heads are reading or writing « 0 »s and « 1 »s onto the magnetic medium so their arms need to be really fast and precise as they are sliding close to the surface of the platter (hundreds of times per second when needed).
Locations are accessed extremly fast by 2 combined movements, as not only the heads are being moved by their arms but the platters are spinning too.
This results in astonishing performance figures: some 40 MB per second can easily be delivered by the hard-disk to the CPU.
But requested data is most of the times made of « chunks » spread all over the platters of the disk.
For example, if you double-click on a spreadsheet file icon, the Operating System will first have to load the spreadsheet app and run it first (that is, assuming that it is not running already) and only afterwards the file is loaded and displayed in the spreadsheet app.
Not to mention the situation when the RAM is full and needs partial unloading by making temporary savings to the paging file on the hard-disk.
That’s a lot of different data and the hard-disk retrieves each piece of information by first seeking its physical location as it needs to be at the right place before it starts reading (or writing for that matter).
Seek time is the time elapsed between the request of a file by the CPU and the delivery of the first byte of that file by the hard-disk.
Usually this is a matter of just few milliseconds so maybe now you will be less bothered by the noises you might hear from your HDD in certain situations: he might be really busy and have some tremendous work to do because of some of your mouse-clicks.
All in all, hard-disks tasks and performance figures are impressive but you need to keep in mind that it is still horrifically slow if compared to speeds of RAM, not to mention the speeds of the CPU.

Before finishing, let us shortly explain three common terms that are related to the hard-disk.
The first one is ‘formatting‘.
To understand what this is all about you need to know that basically disks have ‘tracks‘ and ‘sectors‘.
‘Tracks‘ are concentric, similar to the yearly rings of a tree (the concentric rings you can see in the section of a cut-down tree).
‘Sectors‘ are similar to pie-slices; they all start from the center and can be as thin or thick as wished (depends on the appetite…).
You can now understand that when a platter is spinning it brings a certain sector to the read/write head while the head can position itself on a certain track.
Low-level formatting is the process of outlining the positions of the tracks and sectors on the hard disk and writing the control structures that define where the tracks and sectors are.
These are physical facts so consequently, low-level formatting is said to be the « true » formatting operation, as it really creates the physical format that defines where the data is stored on the disk.
Low-level formatting is performed by the HDD manufacturer and results in a tracks-and-sectors configuration in place but which is empty as nothing is written on it yet.
High-level formatting is done by (and is specific to) the Operating System you are using and it consists in writing the file system structures on the disk that makes the disk usable for storing programs and data (a graphical representation on all structures thus written on the disc is called a ‘discography’).
From that point on, whenever a file will be written or modified, the disk will not only store the file itself but also the « path » to physically retrieve it.
So whenever you are formatting (actually ‘re-formatting’ would be a more appropriate term) your hard-disk, it is only the « paths-to-files » tables that are getting deleted.
No paths, no way to find anything so freshly created new and empty tables might give the impression that actually all information on the HDD has been wiped-out.
It’s pretty much like the Operating System provoked its own amnesia but all informations actually remained written there, although inaccessible.
Inaccessible but not out of reach; some « hypnosis » can be performed if the situation requires as IT experts are able to recover the still-written data on the disk which is good to know in case you have performed a disk re-formatting and later remembered you had precious files on the disk.
Re-formatting with real disk cleanup can be however performed by using special apps (some of which are freely available) which are overwritting the entire disk (even so, old information can still be recovered by some ‘really-skillful ones’ , this is why many institutions for which confidentiality matters (such as the American Department of Defense) have special procedures and regulations on this subject.
So keep this in mind for whenever you will consider selling or donating your old computer.

Another common term related to hard-disks is ‘disk-partitioning‘.
Partitioning is actually a virtual dividing of the hard-disk into one or multiple volumes, each one of these volumes (you know them by their letter names, such as C: , D:, E:, etc.) behaving, from a logical point of view, as if they were separate, isolated hard-disks.
Disk partitioning implies hard-disk reformatting we’ve just presented above.
Partitions were useful on older Operating Systems because they contributed to increasing disk efficiency but the technical reasons behind this are almost history now.
Disk partitioning also allows using more than one Operating System; you can, for example, dedicate one partition to Windows and another one to LINUX.
But again, with virtualization wide-spreading, it will probably become less and less interesting even for expert users.

The last common term related to hard-disks we wanted to mention is « fragmentation« .
This is a naturally occuring situation, when due to frequent use of the hard-disk for writing or modifying files, the Operating System has to store files in a non-contiguous way.
That is, files are being fragmented and different chunks are written in various locations on the hard-disk, rather than a logical-to-physical correspondence.
This is invisible to users but actually it results in longer time and higher disk-usage for file fetching because the disk drive has to lookup multiple places in order to put a file together.
Therefore, de-fragmentation is an optimization process (carried out by special utility apps) by which files are assembled from fragments and re-written on disk in a contigous manner,
to an extend as great as possible.

Well folks, we hope you found something useful for you in today’s article, thank you for reading it and see you next time!

Bye!
Bogdan