April 10, 2002
By Karen Kenworthy
IN THIS ISSUE
Sigh. Life was simpler then. A computer file was a box of cards, or a spool of paper tape. Data was recorded by punching holes in the cards or tape. You could tell a file's size just by looking at it. Other details were visible too. A file's name was likely to be written with a felt-tip pen, along with the name of the file's owner, and perhaps the date the file was created, and when it was last modified.
Simpler, yes. But not better. It could take anywhere from a few minutes, to over an hour, to read a file. It wasn't long before a well-used file became frayed around the edges. Misreads, or errors made while reading the data, were common. And I don't even want to talk about what happens when you drop several boxes of punched cards down a three-story stairwell ...
Winchester 30-30
Fortunately, while I was punching holes in paper, a lot of smart people were playing with magnets. They discovered that you could coat just about anything with a thin layer of an iron compound. You could then store computer data in the coating by magnetizing it in various ways.
As you've probably guessed, it wasn't long before all computerdom was using new, exciting forms of magnetic data storage - magnetic cards and tapes. Oh, and other objects received magnetic coatings too. Large cylinders, called drums, were popular. And several forward thinking people even experimented with flat, round, coated "disks."
The most successful of these early storage devices was born in 1973. That's the year IBM debuted its Model 3340 disk drive. This marvel contained two large coated disks, called platters. Each platter was able to store up to 30 MB, giving the drive its famous code-name -- Winchester 30-30.
Feather-light read/write heads (tiny electromagnets) flew above each platter, riding a cushion of moving air. When the drive stopped, and the air cushion disappeared, a delicate lubricant on each platter prevented damage by the now-grounded heads. The entire package was sealed in an air- tight housing, preventing microscopic contaminants from entering the drive.
Never before had all these features been combined in a single device. And not since has a computer storage design been so popular. Today, almost 30 years later, almost every hard drive found in our personal computers is based on this "Winchester" technology.
File Systems
High-capacity storage devices, like the Winchester drive, were a welcome wonder. But they created new problems for too. Sure, no single data file would ever require 30, let alone 60, MB of storage space. So, what to do with the excess space? Some way had to be found to store two or more files on a single device.
The answer was clear. Drives could no longer hold just the data in our files. Now, they would store information *about* our files too. To make this possible, programmers invented something they called a "file system."
Simple file systems existed before the dawn of the hard disk drive. It was not unusual for a deck of punch cards, or a spool of punched tape, to begin with a short preface describing the data that was to follow. Magnetic tapes often began with a catalog, or list of files stored on the tape.
But the file systems found on hard disks have evolved considerably beyond these primitive beginnings. Today, file systems, and the operating system software that maintains them, have become very complex. To see why, let's take a look some of the information found in the file systems Windows supports:
Unused Space
Keeping track of unused disk space may not seem important. But if this job
isn't done right, disaster can quickly follow. The way a file system
tracks unused space also determines largest usable disk drive. Early
versions of Windows could keep track of no more than 2 GB of space per
drive. But today, Windows NT, 2000 and XP can manage drives as large as 16
exabytes. For people without propellers on their beanies, that's 16
billion GB, or 18,446,744,073,709,551,616 bytes!
File Names
Once a storage device holds more than one file, there must be some way to
tell them apart. Most file systems, including Windows', use file names to
do this job. Early versions of Windows limited file names to just eight
characters, then a period, followed by a three-letter "file name
extension". This is often called the "8.3 file name convention," and if
they ever hold one in your neighborhood, it's worth attending. :)
Today, Windows' file systems allow file names containing as many as 255 characters. Under Windows NT, 2000, and XP, file names can also include characters from the Unicode character set, covering most of the characters in the world's major languages.
File Sizes
Naturally, a file system must keep track of the size of each file. Within
Windows' file systems, this information is kept in a 64-bit unsigned
integer. As a result, the largest possible Windows file size is currently
18,446,744,073,709,551,615. Yes, that's 16 exabytes, the same as the
largest usable drive under Windows NT, 2000 and XP. But don't worry -- a
future version of Windows will lift this onerous limit. :)
File Times
Windows's predecessor, DOS, only kept track of when a file was last
modified. But today, Windows records three dates and times for each file:
Date Created, Date Last Modified, and Date Last Accessed (read or
modified).
File Attributes
Most long-time Windows users are familiar with the four most famous file
attributes: Read-Only, Hidden, System and Archive. Obviously, read-only
files can be read, but not written. Hidden files are not normally visible
in lists of files on a drive. System files are those used by the operating
system, and Archive files are those that have been modified since the last
time they were backed up.
But did you know that under Windows NT, 2000 and XP there are several additional file attributes stored in the file system? These extra attributes include Compressed, Encrypted, Temporary, and Offline.
File Security
Early versions of Windows didn't care who accessed your files. But today,
security is much more important. Windows 95, 98, and Me maintain a list of
who can access each "share," or folder available to others on a network.
Later versions of Windows also allow the owner of individual files and
folders to specify who can access those items, and the type of access
others are granted (read-only, read/write, etc.).
Updates
If you'd like to learn more about the file systems on your drives, and a lot more, check out the newest versions of two popular Power Tools, Computer Profiler and Drive Info.
Computer Profiler v1.8 now displays more file system info than ever, including the maximum file name length, and the a drive's cluster size (the smallest amount of disk space that can be allocated to a file). The program also sports some small improvements that make a big difference to users with visual impairments, and others who rely on keyboard navigation.
To give this new Profiler v1.8 a try, visit its home page at:
https://www.karenware.com/powertools/ptprofiler
And while you're on the web, check out Drive Info v2.0. This Power Tool now uses an easy-to-read grid to display information about each of your drives. New information includes the maximum file name length. To download your copy, drop by its home page at:
https://www.karenware.com/powertools/ptdinfo
As always, both programs and their Visual Basic source code, are free.
Or, if you prefer the convenience of a CD, or want to support Karen's Power Tools, visit my CD page at:
https://www.karenware.com/licenseme
Your copy of Karen's Power Tools CD will include the latest Profiler and Drive Info. It also has the most recent versions of every other Power Tool, including three bonus Power Tools programs not available anywhere else. It also includes a special Web Update program that automatically keeps all your Power Tools up-to-date. The CD even includes every back issue of my newsletters, and a special license that lets you use all the Power Tools at work!
Well that's all for now. For some reason, I suddenly have this urge to dig through my closet and find some old punched card decks. Until we meet again, if you see wandering down memory lane, or on the 'net, be sure to wave and say "Hi!"
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