[X Newbies] jpegs, etc.

[Florin Alexander Neumann]

On Friday, May 16, 2003, at 23:00 Canada/Eastern, Anne Keller-Smith 
wrote:

> Just out of curiosity, has the Mac always not wanted to open
> documents like this? I thought it did not care what a document
> was named.

and

On Sunday, May 18, 2003, at 13:55 Canada/Eastern, TheMacintoshLady 
wrote:

> In X it does want to know, just like Windows used to but now doesn't
> because it wanted to be more "Mac-like". Now Mac is more like Windows 
> 3.1
> It needs the file ending, and the exact file ending.

This goes back to a basic problem. How does the computer know what kind 
a particular file is? One way is to include this information in the 
file itself. For instance, PNG files always begin with "âPNG". Another 
is to include it in the file name -- e.g., "My Picture.png". This is 
what Windows (still) does. Yet another is to include this information 
neither in the file itself, nor in the file name, but in the file 
metadata, i.e., in the information about the file. This information is 
present in a database maintained by the operating system. Each method 
has its pros and cons.

Macintosh used the latter option. For each mounted volumes, Finder 
maintained a database with information about each file, including a 
four-character Type code, e.g. "PNGf". This code was invisible to the 
user, who could only access it with utilities such as ResEdit or File 
Buddy.

Simply copying a file from Mac to Win or viceversa will not transfer 
this information, because Windows doesn't know anything about Mac type 
codes. And, since Mac users were only a small minority of computer 
users in general, there was no need for Windows to learn how to handle 
them. As a result, Mac applications and then the OS acquired the 
capability of handling file name extensions. In OS X (which, under the 
hood, is not really Macintosh at all), both methods are supported.

Of course, this doesn't mean that the system is foolproof. If a Win 
user sends you a file named "My Picture.jpg 1", neither OS X nor 
Photoshop will be aware that ".jpg 1" is the same thing as ".jpg", and 
that the file is supposed to be JPEG. So what do you do? You can change 
the file's name from "My Picture.jpg 1" to "My Picture.jpg". Or, you 
can use a utility such as File Buddy or SuperGetInfo to change the file 
type to "JPEG".

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