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The Storage Tree - Understanding the Hierarchy of
How Files are stored on PCs
I often come across PC users who store the files they create on
either their Desktop or in
My Documents as those are the only places they feel
confident of being able to locate them again.
If a CD ROM doesn't "autoplay" when they close the drive door, or a
USB Flash drive doesn't automatically open a file listing window, then
they're stuck.
They know how to download a file from a website but where it disappears to
after it's downloaded is a mystery.
Making backups, organising files more logically and conveniently or
deleting files are way too hard.
Many, more experienced, users still only have a vague understanding
of what the options are for storing files and how all the various
locations are interconnected to form the overall Storage Tree.
So, on this webpage, we've tried to provide the explanation that
every new PC user should receive before starting to work with files.
No matter how user-friendly or intuitive a computer system may be, dealing with
files is an inescapable part of what you'll need to do to keep your
important data safe and accessible.
Getting the Basics out of the Way
What is a file?
A file is a group of 8 bit binary numbers which, when taken together
and in the correct order, form a unit of information such as a Word
document, a picture, a video or a piece of software.
For such an Information Unit to be a file it also needs to be stored on a
medium which has a degree of permanence so that it will continue to
exist after the storage device containing the storage medium is turned off.
An Information Unit stored in a computer's main Random Access Memory
or in transit across the Internet isn't a file.
A file also needs to be able to be read from its location either into
computer memory or onto another storage device. This requirement means
that a picture displayed on a computer monitor isn't a file and the
paper printout of all the binary number contained in a file also isn't a file.
A file can be any length from zero (8-bit) bytes to many gigabytes. The
maximum size that a file can be is limited by the computer's operating
system and the capability of the storage device.
This limit is gradually being extended upwards as a practical use is found for larger files.
It's worth pointing out that even a zero-length file will use up over 4000 bytes of hard drive
storage, as storage devices allocate storage space in fixed sized chunks.
A high quality video file may be 4gb which can be stored on a DVD.
A file that holds the "image" of a hard drive can be many 100s of
gigabytes which can only be stored on another hard drive or perhaps a
magnetic tape.
A file also has "attributes" which are a combination of
special file properties and data that describes the file. Data that
describes data is usually called as metadata.
These attributes are usually stored separately from the
file in a storage medium's "table of contents". Such attributes include
File name, file size, time and date of last modification, read-only,
compressed or encrypted.
When a file's read-only attribute is set, this is just a signal to
the operating system not to allow the file's contents to be changed.
If a file's "compressed" or "encrypted" attributes are set then the whole
contents of the file will also need to replaced by new data that is
related to the original data by some mathematical formula that either
makes the new data occupy less storage space than the original or makes
it unreadable unless a "key" is provided to allow the mathematical
process to be reversed.
The compressed and encrypted attributes are
unusual in that they actually affect the data itself. All file systems I
know of, allow files to be encrypted or compressed, but not both
at the same time.
A Windows XP Explorer window displays a file in blue to indicate
it's been compression and green to indicate
it's been encrypted.
A new installation of Windows XP consists of around 30,000 files and,
after many months of use, this can have grown to 300,000 or more.
Where have all these files come from?
Here's an example of what these files might consist of and how they've
got onto your PC:-
| |
File Category |
Source |
40% |
Windows operating system and
associated files
System files
Configuration files
Driver files
Log files
Help files |
Windows installation CD and Windows Update Website |
30% |
Software programs you have
installed |
Program installation CD or installation files,
downloaded from manufacturer's website |
15% |
Files you have downloaded
MP3s
Videos
Digital camera pictures |
iTunes website,
Peer-to-peer networks,
Your digital camera |
10% |
Files created as an indirect
result of your actions
A web browser's cache of the
web pages you've visited |
Downloaded from the Internet or a temporary
file created by a program for its own use |
5% |
Files you have actually created
yourself
PowerPoint presentations
Budget in Excel
Home movie |
Created in applications such as Microsoft Word |
I'm not sure what category a virus or spyware fits into, but let's
assume you don't have any on your PC.
What is a folder?
A folder is a storage location on a storage device that can contain
files just like a real cardboard or plastic folder can contain pieces of
paper.
A file-system folder can also contain other folders that can
themselves contain other folders and this is where the analogy to real
folders breaks down.
The purpose of folders is to organise files into logical groupings so
that humans can more easily find one particular file and so make sense of
the large amount of files, in total, on a storage device such as a hard
drive.
Compartmentalising objects is a common strategy that humans use to
organise and control large numbers of objects:-
Fresh food in the fridge, frozen in the freezer, cereals and packets in
the pantry cutlery in the cutlery drawer, cleaning materials in under
the sink, coffee mugs in the cupboard above the kettle; this way, we
can quickly find any object we need in the kitchen.
Like real folders, a file system folder has a name and a location:-
Store-room 2 - Filing Cabinet 4 - 3rd drawer down - at the back -
"Invoices April 2007"
A file system folder's location is its position in the hierarchy of
other folders on the storage device.
A file-system folder also has attributes for instance it may be hidden and although you can set a folder
to be encrypted, compressed and set access permissions to control who
can do what with it, it's really just the files contained within the
folder that are compressed, encrypted etc. rather than the folder
itself.
If an unencrypted file is copied to an encrypted folder
then the copy is automatically encrypted.
A folder only "exists" as an entry in the Table of Contents of a
storage device.
If you were to examine how the files themselves are
distributed throughout the storage device, there would be no folder
structure apparent.
Folders, being a device to help humans organise files, are far less
important than files and the only real data they contain is their name.
We generally create files and folders on a hard drive without
considering that there are finite limits to the number and size of the
files that can be stored in a folder and the number of times you can
place a folder inside a folder inside a folder.
Fortunately drive manufacturers and operating systems keep extending
these limits so that it's unlikely that we will ever manage to exceed
the current limits that apply to the system we're using.
The only limit I've come up against in recent times is a CD writing program warning me
of the limit of 8 nested folders allowed on a CD.
In storage devices, it's OK to have multiple files and multiple
folders with the same name as long as they're not in the same location
in the file system hierarchy.
A folder also cannot contain a file and a folder with
the same name as each other.
In any case, it's a good idea to avoid having multiple files and folders with the
same names.
The top of the folder hierarchy in a storage device is called the
top-level folder or root folder, it's the only folder that isn't a
sub-folder.
The folder above the current folder can be called the Parent Folder.
Directory is a term that means exactly the same as Folder in file
storage systems but has dropped out of use in recent times however you
may still hear the term, especially Root Directory for the top-level
folder.
Where can files be stored?
The "Filing Cabinet" metaphor
What's all this about trees?
The way that folders are created and the way that files are stored in
them can be compared to how a tree grows where braches split off other
branches and leaves grow.
The root system of a tree has a similar shape to it's branches and so
some people take the
file-system tree metaphor to mean a tree's
root system.
I think it makes more sense to view it as the branches
of a tree only turned upside down because the root system has no
equivalent to leaves which represent files.
Upside-down branches or roots, use whichever analogy makes most sense
for you.
Why Microsoft doesn't help.
The Bent Up-Arrow and Breadcrumbs
When you are viewing an Explorer window, displaying files and folders
at some location in your computer's Storage Tree, you are looking
downwards, deeper into the storage tree, as if floating face-down on the
ceiling of the current folder, and so you can't see what's above you.
Even the folder immediately above your present location is not visible.
It's easy to move down deeper into the storage tree by double-clicking
on a folder but moving upwards is harder.
That's what the bent up-arrow icon does, it moves you up one level in the storage tree.
In the Tree/Branch system, while a folder may have any number of
sub-folders, it can only ever have one folder above it,
called the Parent Folder, so the bent up-arrow only ever has one place to send you.
Repeatedly clicking the bent up-arrow will get you to the Desktop, even if it takes
10 or more clicks.
Going back further into computing history, 2
horizontal dots mean the same as the bent up-arrow symbol and you
occasionally still come across this symbol today.
The dual-pane Explorer window you get when you run Windows Explorer are more
flexible than the single pane window because the left-hand pane makes it
easy to move up and down the Storage Tree.
This is why Windows Explorer should be the first program you run to perform all but the simplest file
operations.
Outside of this program, all other Explorer windows are
single-pane where the bent up-arrow is so useful.
No Bent Up-Arrow in Vista
Yes, Microsoft have decided that there's
no place anymore for the bent up-arrow in Windows Vista. Just when
you've learnt something useful it's thrown in the bin!
The bent up-arrow has been replaced by a breadcrumb trail.
In the story of Hansel and Gretel by the Brothers Grimm, after overhearing their
parents' plan to lead them into a forest in order to abandon them, the
children successfully find their way back home by following a trail of
pebbles they dropped on the way out.
On the second attempt to lose them in the forest, they only manage to find breadcrumbs to drop, and when they come
to follow this trail home, they find that the breadcrumbs have been eaten
by the animal of the forest.
In recent years a new navigational aid has appeared on websites: a
horizontal line near the top of the page showing where you are in the
website and the path back to the Home page.
This is called Breadcrumbs.
In Vista, Explorer windows show the
trail back up the Storage Tree hierarchy, and clicking on an entry on
this trail gives a drop-down list of all the deeper locations that can
be reached from that point.
Breadcrumbs are therefore more powerful than
the old bent up-arrow as you can jump up and down to more locations in
one click.
I miss the bent up-arrow in Vista and would have liked it to
be displayed as well as the Breadcrumb Trail.
Breadcrumbs require more brain CPU cycles to work out what you want to do,
especially if you only want to jump up 1 or 2 levels.
Microsoft Promotes the Desktop to Become the New Super-Root Folder
The first PC, released by IBM in 1981, had a single floppy drive
(actually an optional extra) and so the top level folder of a floppy
disc was obviously the Root of the Storage Tree - nothing complicated here.
In fact there was only the Root, as sub-folders only
became available after an update to PC-DOS. Later, some PCs had 2 floppy
drives and a 10mb hard drive - (75,000 times smaller than today's
largest hard drive) - and, much later, a CD ROM drive and a mapped
network drive.
The top level folder of each storage device was called
the Root and, like separate trees in a forest, all seemingly unconnected
and you "jumped" from one device to the other as necessary.
In Windows 95, Microsoft made a new, higher level super-root,
root-of-roots, that established a single top-level point, uniting the
storage devices, from which all possible file storage locations,
accessible from a PC, branched off from - no more jumping.
They called this super-root the Desktop and it's still with us today.
The problem with adding locations in the Storage Tree, higher that
the root folders of a storage device, is that they aren't real
locations in which real files can be stored.
In fact Windows 95 introduced 4 new Storage Tree locations:-
The Desktop
My Computer - now called just Computer,
Network Neighborhood - renamed My Network Paces and again to
just Network,
My Documents - also sometimes called, for instance, "John's
Documents".
My Documents doesn't count as is not an integral part of the Grand
Unified Storage Tree. I'll tell you why a bit later.
My Computer is a location below the Desktop and contains
storage devices that are present locally on the computer you are using;
the ones you can see with the system box case open.
Network is also a location below the Desktop which contains storage
devices "somewhere else" - across the room or across the world.
Both Computer and Network are concepts, virtual locations which
cannot, themselves, contain files or folders and are useful as
"signposts" to the files you want to find.
The Desktop is much cleverer than that as it can store real files and
folders.
The Desktop is 3 things
1 - The graphical menu you see immediately after logging on which
contains icons allowing you to quickly access the programs and files you
use most often.
What's clever is that every user of a PC has their own
Desktop, customised for their needs, including such irrelevancies as
Wallpaper, Screen-saver, mouse pointer and system sounds.
In Windows 3.1, the predecessor of Windows 95, this was all
that the Desktop was.
2 - The conceptual super-root of a computer's Storage Tree.
This is a very different role to being a graphical menu and is
something that users' often don't realise.
Microsoft decided that a single unified storage tree was better than
having many storage device trees in a forest - Linux has always worked
with a single root - and, rather than invent a new super-root object,
they chose to make the Desktop do double-duty.
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