Magnetic tape filesystem

Nico de Jong nico at
Mon Feb 9 13:03:17 CST 2015

> All this talk about magtapes brought some memories to the fore.
> While a single tape drive was the rule for personal computers, it 
> certainly wasn't that way for mainframes.  In particular, one very 
> important aspect was sorting (and, by extension, merging).  The wonder of 
> a polyphase (or better yet, oscillating) sort running on a bank of 8 300 
> ips drives was mesmerizing.
> Undoubtedly, the folks before me who spent their time shuttling trays of 
> punched cards around an IBM 082 have a similar reaction to the "easiness" 
> of tape sorts as compared to card sorts...
I remember a regular job (every week....) in my servicebureau where I had to 
sort about 40.000 200-byte records on a DOS machine. DOS did have a SORT 
command, but it was horribly insufficient.
I therefore had to get back to my experience as IBM 82 operator (!), and do 
it more or less that way. The first stop was to create x files, each 
containing about 1000 key fields. When the input was read, I would sort one 
keyfile at a time internally and write it to a new file. After the sorting, 
I merged two indexfiles and write a new file, etc. When all indexfiles were 
merged into one, I found the respective full records, and wrote the output 
It took about 15 minutes or so for the whole job, but the customer was 


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