...a Disc Interchange technical article
What We Need to Know to Convert Your Files
This article discusses what information we need to know to convert your files between different computers
and operating systems.
Platform conversions are usually tape conversions, so that's what we'll discuss here. Disks have similar
- The type of media.
- The density or mode the tape is recorded in.
- The computer and operating system the tape is from.
- The method or program used to write the tape.
- The type of file(s).
- The record layout(s).
Each of these is briefly discussed below. We will need to know this information for both the computer
you are converting from, and the one you are converting to. We have chosen to keep this discussion brief, so the issues
are abbreviated, and of necessity, incomplete.
The type of media
Obviously we need to know the type of tape or disk. We seldom care about the brand; just
the type. If you are not sure what you have, see Identifying Media.
Recording density or mode
Some tapes can be recorded in many densities or modes, including
different numbers of tracks. We need to match the density and number of tracks before reading the tape. We can generally
figure this out by inspection when reading a source tape (the tape you are trying to convert from), but you should tell
us which density you want us to write if we are writing a destination tape.
The computer and operating system the tape is from
The operating system dictates both the content of the files
and how they are written to tape. This is critical information. However, in the case of some standard tape formats, like
mainframe tapes, we don't need to know the operating system if we know the standard format used (#4 below). This is
sometimes true of UNIX tar and cpio tapes as well.
The method or program used to write the tape
Each operating system has several ways to write a tape. In some
cases, such as mainframes, minis and UNIX, the tape software is part of the operating system, so if we know the
operating system and the tape utility used, we generally know the format. If you have a mainframe tape, we only need to
know that information, not the exact OS version.
In other cases, especially MSDOS, Windows, and NT, the tape software, and therefore the tape format, is often a
third-party product. Each of these third party products writes a different format, so we need to use the same product to
read or write the tape. Many products are not even compatible between different versions of the same product, so please
try to get the version, too.
The type of files
DISC converts many different types of files, and the issues are different for each. We
need to determine the type of file on the source media, which we can sometimes do by inspection, and you will need to
tell us what file type you want back.
The record layout
(If these are database files.) If DISC will be converting any binary numeric fields we will
need the record layout to write the conversion program. If we are only doing an EBCDIC to ASCII conversion of all
character fields we only need the record length, although sending a layout is still encouraged so we can more thoroughly
check the data.
In some cases we can determine much of this information by inspection, but it's still best to get as
much information as you reasonably can.