I love this operating system and cannot wait until the first release of Haiku is available. BeOS was/is one of the most responsive and usable operating systems I have ever used. It has features that even current systems do not yet come with, for a history lesson have a look at this OSNews article. It is hard to explain all of the virtues of BeOS unless you have actually used it, but I will give it a go.
File System
BeOS had a powerful journelled 64bit file system. This allowed a maximum file size of 18 million gigabytes (just a tad larger than current hard disks) and full recovery in the event of system outages.
It also had the concept of extended and custom attributes. Examples of file attributes include Size, Name, modified date etc, however BeOS took it one step further. Each file in the filesystem had a MimeType attribute, this dictated (via a standard notation) the type of file. Unlike Windows that relies on file extension this attribute a file in BeOS can be called anything an this attribute dictates what it is.
The next thing it does is allow custom attributes based on the file type. This allowed file information to be stored outside the file in an indexed area allowing for fast searches. An example is images, they had custom attributes of width, height and colour depth. This means you can search for images that are no larger than 120 pixels wide and greater than 16 bit colour depth. Now lets extend that to emails, all of the standard headers are exposed in attributes, meaning you can search on sender, send date and any other you can think of. Now the really interesting upshot of this is that BeOS does not come with a mail client. It does have a little program for reading, editing and creating individual mails but the standard file manager is used as the mail client.
Data Translators
If you have ever played with image editing tools in any operating system you know that each one has its own mechanisms for reading and writing image formats. Photoshop, Paintbrush, GIMP etc all have their own code and options for image formats they handle. I have heard of people editing images in one tool, just to open them in another to save them as a JPEG, because the second tool has better optimisations for compressing and saving JPEG’s. Well in BeOS no image editing program knows how to read and write any image format, they only understand the underlying bitmap format that is used to render onto the screen. Yep you read that right, no program written for BeOS know how to read and write an image of the disk.
The BeOS engineers realising that all this duplicated code was a waste, they implemented the Data Translator mechanism. What this means is you decide what translators you want to install and the programs just call up the list and let you select. This means that you can save and open all formats in all programs, that support images. This was also extended to documents, and via central codecs, videos and sounds.
Resources
Now a version of BeOS was released free for use, so looking up the following resources you will find a copy if you want. Be warned however this is an older operating system and may not work on the newest hardware.