At 8/13/98 02:56 PM , Eric Bender wrote:
>At 11:18 AM 8/13/1998 -0700, Donna Garverick wrote:
>>i guess this is an oldie but a goodie sorta question...
>>
>>how much information can a 2400' reel (yes, reel) of tape
>>contain -- in theory.  i guess, perhaps, the better question
>>is -- does anyone remember the equation for calculating
>>this?       - d
>>
>>--
>>Donna Garverick     Sr. System Programmer
>>925-210-6631        [log in to unmask]
>
>
>So, assuming no Inter-Record (or Inter-Block) Gaps, at 1600 BPI that would
be:
>
>1600 x 12in/ft x 2400 = 46,080,000 bytes  (46 MB)
>
>and at 6400 BPI it'd be 184,320,000 bytes (184 MB).
>
>So, with IRG's and labels and other overhead, actual values would be less
>than these theoretical calculations.
>
>Regards, Eric Bender
>
>PS. Someone check these calculations. Please!
>

Well, I seem to remember the IRG as being 0.5 inch.

Assuming the record size to be 16,384 bytes, at a tape density of 6250 bpi,
a record (16K bytes) takes up approximately 3.1214 inches of tape
(including the 0.5 inch IRG).  An "average" foot of tape should hold
62,847.92 bytes.  Multiply by 2400 and the capacity becomes 150,834,999
bytes.  In the "real world" you will probably get somewhere between 130Mb
and 151Mb per reel.  No, the 151Mb is not an error.  Remember, when writing
to tape it is possible to write several feet past the EOT mark, and STORE
often does so.

As to 1600 bpi tapes, the capacity calculations are: 10.7400 inches per
record (including IRG), or 18,306.15 bytes per foot, or 43,934,748 bytes
per 2400' reel.

John
--------------------------------------------------------------
John Korb                            email: [log in to unmask]
Innovative Software Solutions, Inc.

The thoughts, comments, and opinions expressed herein are mine
and do not reflect those of my employer(s), or anyone else.