What's magtape good for anyway?

[Allison J Parent]

<There are certain areas of Unix that don't seem quite "done" to me. 
<Printing comes to mind (compare Unix benign neglect with Windows'
<universal printer driver).  

Most of magtapes short commings under unix are common across most OSs
and are assignable to the characterisitcs of the medium.  Mag tape has
several things that make it difficult, one is old (late 60s and through
the 70s) drives had a difficult time starting and stopping without 
breaking tape or resorting to complex(then standards) controllers.  This 
lead to things like large interrecord gaps (start, speed up read, stop,
backspace records, stop, read) due to the inerta of starting and stoping 
the reels.  Also fixed record sizes were used to make blocks about the 
same length so blocks and marks could be differentiated using simple 
timers.

Magtape was for the longest time the only portable media, which lead to 
the ansi/EBCDIC problems (Evryone else and IBM/HP).  It was generally 
used for archival storage making file organized access excess overhead.  
While often used as block oriented, many systems used it more as a stream 
device where the high volume storage (relative to the disks of the time) 
capability was available.

When processing was done on early system usually two or three drives were 
involved as one of two were for reading  and the third was writing results
usually due to memory size limitations of the time compared to the amount 
of data.  Alot of magtapes lore is a result of historical use.

FYI the idea of tar files had spilled over to CP/M (8080, z80) systems 
back in the 80s for distribution sets.  It was done usually by creating
an archive set of compressed files (.arc, .ark, .lbr). to get the most 
out of limited space of floppies (under 300k) of the time and to keep 
programs set and sources together.


Allison


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