Subject: RE: On PDFs
From: "Miller, Alan" <Alan -dot- Miller -at- prometric -dot- com>
To: "TECHWR-L" <techwr-l -at- lists -dot- raycomm -dot- com>
Date: Thu, 24 Apr 2003 16:22:24 -0400

rbilbao -at- us -dot- amadeus -dot- net asked:
>>Does anyone know where I can get some cold hard facts about PDF download times?<<

Easy question. <Rhetorical question>So how come nobody's answered it yet?</Rhetorical question> The answer is: "In your calculator." :-{) Use this simple formula:

File size (bytes) / Transfer rate (bytes per second) = Time for transfer (seconds)

If your file size is given in kb, multiply by 1024 to get bytes (a kb is *not* 1000 bytes; it's 2^10 bytes, or 1024). Likewise, multiply Mb by 1,048,576 to get bytes (a Mb is 2^20). Then, divide by the transfer rate (56,000 bytes per second; this time kbps *is* 1000 bytes per second).

If you have a 1 kb (1024 bytes) file to download at 56 kbps, you get:

1024 bytes / 56,000 bytes/s = 19 s (rounded to two significant digits, the lowest precision of my input numbers)

Hmmm. Looks like a thumb-rule to me: 1 kb at 56 kbps = 19 s

If you want minutes, divide by 60; for hours, divide by 3600.

This calculation will return the *optimum* download time. Many factors can significantly increase the actual time. Several users sharing a line, for example. In that case, a good estimate would be to multiply the time by the number of users sharing the line at the time of the download.

Glad you asked?

Al Miller
"Chief Documentation Curmudgeon"
Prometric, Inc., a part of The Thomson Corporation
Baltimore, Maryland

A lie gets halfway around the world before the truth has a chance to get its pants on.
-- Sir Winston Churchill

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