"File types"

Chuck Guzis cclist at sydex.com
Mon Aug 28 21:21:26 CDT 2006


On 8/28/2006 at 4:47 PM Don wrote:

>No, those are file *permissions*.

Are you asking, "Did any system keep file type information out of the file
name?"  The answer is "yes, several did".  Here's part of a microcomputer
floppy directory from a circa 1977 OS.  Note that fiile dates show this
disk was probably created around 1986 (yes, it's all in ASCII--no binary
fields here):

A$DIRECTORY	000000001500000016	SF 	064032386                       
ACONFIG.SYS	000160001610000016	DV 	000010199                       
AMT.PARTS  	000170001702700017	DV 	000010199
ADX85M26D03	000180004643600046	LV 	000080483
AISAM.SYS  	000470005814400058	SV 	000080483
A$AUTOSTART	000620006201300062	PV 	000080483                       
ARUN       	000630009348700093	SV 	000080483
AMTMENU    	001120013036800130	OV 	000010199                       
ALOCATE    	001310014242700142	OV 	000010199                      
A$SBA.C    	001430014400000143	II 	003               
A$SBA.C@   	001450014800000145	MF 	055

First column is the file name, the second is the file allocation and length
information.  The third column is the file type and the record type.
S=System D=data,  L=boot loader, P=profile, O=binary object, I=ISAM index,
M=ISAM data (there are other types).  The second characters is the type of
record F=fixed, V=variable, I=index.  The fourth column is the record
length and the creation date.    By convention, ISAM index files take the
name of the data file, with an "at" sign appended, though there was no
particular system requirement for this.

If you enter the name of a file that didn't have the O file type, the
system won't execute it.  Similarly, you can't open a file with anything
other than the DV attributes for text display or editing.  ISAM files are
handled by the ISAM manager and nothing else.  You can't do ANYTHING with S
or L  type files, not read them, not write them directly.

I've seen other systems from the 70's with this kind of directory
information.   However, the idea of a file extension for certain types of
files was contagious--note the CONFIG.SYS (well in advance of MS-DOS).

Cheers,
Chuck





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