by X Zhu (Ph.D.), May., 2003
* Feel free to copy but do keep content complete, author Email: itreviews@ntlworld.com
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1. Introduction
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Related topics |
It is always worring if the file saved by PC in the portable hard drive or pendrive or ZIP drive can be opened by MAC? or save by MAC to be opend by PC? There are problems, here is a guide how to avoid the problem by choosing the right file format.
In order to use Mac formatted drives on Windows systems, special software such as MacOpener is required.
To open PC files in MAC, use PC exchange, which is part of MAC O.S. 8.1 and later.
File Systems
A file system is a structure that organizes large numbers of files on some sort
of recording medium such as hard drive, CD, and DVD. The idea is to store the
files on the disk so that they can be accessed randomly and with minimal time
delay. The PC and Mac differ in the way they store files. These differences
can make it difficult when copying files between platforms. Not all Mac files
will be useful on a PC and vice versa. Executable program files compiled for
one platform can not be used on the other, but there are many that have a separate
version for each platform.
Mac Files
On a Mac each file can have two parts called forks - a data fork and a resource
fork. These are actually two files linked to one name in the Mac file system.
The resource fork holds resources (icons, fonts, menus, sounds, etc.). Since
each resource fork can hold many resources, it has a specific structure that
allows programs to find and access a particular resource quickly. The data fork
can hold any type of data (text, images, etc.) and does not have a required
a structure like the resource fork. Mac resource forks are generally of no use
on the PC, but it is possible for a PC program to convert specific resources
to a PC format. Our program CrossFont can do this with Mac fonts which exist
in the resource fork. The contents of the Mac data fork is usually all that
can be used on a PC. Once a Mac file is copied to the PC, the resource fork,
type and creator information are lost unless the file is encoded with MacBinary
or a similar format (HQX, SIT, etc.) that saves the Mac specific data with the
file. This way the file can exist on a single fork machine (PC, UNIX) or be
telecommunicated and decoded at the other end with all Mac information intact.
It is useful to have a way to identify the type of a file as well as which application created it. The Mac file system has this information stored with the file name and other information. They are two four character fields called the type and creator. Mac programs can use many different types of files. The type field tells the program what type of data is in each file so it can parse it properly. It also allows a program to filter files in an open file dialog box so the user can only open files of a certain type. The creator field is unique for each Mac application. When an application creates a file, it puts a creator signature in this field which identifies that this application should be launched when a user double clicks on the icon of the file.
PC Files
Unlike the Mac, PC files only have one file linked to each name. Copying PC
files to the Mac should be no problem. The PC file becomes the data fork of
a Mac file. When Mac files are copied to a PC, their resource fork is usually
left behind or copied as a separate file (as PC Exchange does) unless the file
is encoded as explained in the above section.
PCs have a different way of identifying a files type. This is done with an extension to a files name. The extension is the characters after a period at the end of the file name. It used to be limited to three characters in the DOS days, but it can now be larger. Instead of a separate creator field like the Mac, each extension is associated with an application. This is much less flexible than the type and creator fields on a Mac.