2 Mar
2009
2 Mar
'09
11:36 a.m.
From: bfranchuk at jetnet.ab.ca
Sent: Thursday, February 26, 2009 1:19 PM
Mike Loewen wrote:
> On Thu, 26 Feb 2009, Gordon JC Pearce wrote:
>> Didn't someone once work out that to store
a single MP3 you'd need a
>> stack of 80-column cards ten miles high?
> Assuming a 6MB MP3 file and 40 bytes per card:
> 6 * 1048576 = 6291456 bytes
> / 40 bytes per card = 157286.4 (157285) cards
> * .178mm card thickness = 27996.73 mm high
> / 25.4mm per inch = 1102.233465 inches
> / 12 = 91.85278871 (91.85) feet
Umm if you store binary ... that is 80 bytes per card
.. 46 feet per file.
Now how many dec tapes is that?
We'll assume a PDP-11 DECtape since we're discussing 8-bit bytes. Depending on
how we map those, the numbers can come out the same for PDP-1/4/7/9/15 and
PDP-10 tapes; PDP-5/8/12 tapes *will* be different.
A PDP-11 DECtape consists of 577 sectors of 256 words (= 512 bytes) each. If
we assume a non-directory tape (that is, written with a user program instead of
OS services), we can put (* 578 512) = 295936 bytes on a tape, so we will need
(/ 6291456 295936) = 22 DECtapes; there will be only (- 6291456 6214656) =
76800 bytes on the last tape.
If we instead choose to use a DECtape initialized by one of the various OSes,
we lose different numbers of blocks per tape depending on OS. For example, if
we use a Files-11 layout (RSX/IAS), we lose at least 10 blocks to filesystem
overhead (5120 bytes) per DECtape.
Rich Alderson
Vintage Computing Server Engineer
Vulcan, Inc.
505 5th Avenue S, Suite 900
Seattle, WA 98104
mailto:RichA at vulcan.com
(206) 342-2239
(206) 465-2916 cell