From: vail@tegra.com (Johnathan Vail)
Subject: Re: SCSI bad sectors?
Organization: Tegra-Varityper, Inc. Billerica, MA
Date: Wed, 30 Sep 1992 14:49:43 GMT



In article <BvDonz.KJv@iat.holonet.net> bwilliam@iat.holonet.net (Bill Williams) writes:

   I do not have the Seagate 4702N manual around me but beware of some lying
   jerks that abuse the phrase Megabyte to mean 10^6 th power bytes instead of
   the computer science meaning of 2^10 th power Kilobytes . Only *ONE* company I
   have ever ever heard of tries to use the printed word "Megabyte" to meand the
   smaller evil 10^6th meaning and that company is QUANTUM. To be fair, the
   word "Megabyte" when written in tech manuals by QUANTUM is usually always
   preceded by the word "Quantum" as in "200 Quantum Megabytes" with "Quantum
   Megabytes" being explicitly defined as 10^6.

It seems like you are picking nits or have an axe to grind.  Either
way you calculate it there isn't that much difference.  And I am not
convinced that 2^10 K is a correct way to measure it.  The quick
(small and not scientififc) survey of manuals I had right here I
couldn't find anyone who measured that way (see below).

And don't consider this a flame.  I looked into this a while back and
decided on 10^6 for my calculations.  If this is not right I would be
happy to be corrected.

Anyway, 10^6 = 1,000,000.  2^10 "kilobytes" = 1,024,000 or a
difference of %2.4 or less than five blocks for a 100 "meg" disk.

   Imprimis/Seagate, Maxtor, Conner, Fujitsu, HP, DEC, MOST, IOmega, INSITE
   etc all universally use the printed word Megabyte to mean 2^10 Kilobytes
   though advertisement oriented spec sheets play games with the Symbol "MB"
   which can mean Megabits Megabytes 10^6 or 2^10....

In the manuals I looked at only Quantum actually defined the symbol.
Calculations suggest that others use the same units as Quantum.  IBM
apparently rounded to the nearest 100 MB so either unit calculation
works fine.

   "MB" means *NOTHING* because of abuse. Get printed specs that use the word
   "Megabyte" only. If you can find such a document, then your next step is
   to connect the formatted device to a specialized program that will report
   the current number of available blocks on the disk (remember that such
   programs might report the last addressable block, and since SCSI is 0
   based add 1 block to the total blocks available.

I did that and couldn't find any evidence of 2^10 K in the ones I
looked at.  Maybe you could post

   DOS 5 might have to remap in a bad manner.

huh?  I don't what this has to do with anything but the number of
blocks returned by READ CAPACITY is gospel and is not affected by how
you calculate megabytes.  Any mapping would probably be done via MODE
SELECT pages on the format and geometry of the disk.

   I do not believe the SCSI docs intended to lie and ever count the
   remapping areas (very large on optical disks) as valid blocks in the
   Megabyte calculation)

   Also..... Many greedy marketing pigs round up the megabytes to the next
   higher number and never routnd down like they should (they are MBAs and
   not technically trained)

   AND SOME crappy companies round up incorrectly, such as 119.1 Megabytes
   being referred loosely as a 120 Megabyte device.

Maybe there is some confusion about formatted and unformatted
capacities.  Unformatted capacities seem to appear to consist of just
a raw product of cylinders, heads and bit per track.  This would
include blocking format data and sparing areas.  Any formatted
capacity would natually be significantly less.


jv

 _____
|     | Johnathan Vail     vail@tegra.com     (508) 663-7435
|Tegra| jv@n1dxg.ampr.org    N1DXG@448.625-(WorldNet)
 -----  MEMBER: League for Programming Freedom (league@prep.ai.mit.edu)



A QUICK SURVEY OF THE MANUALS AT MY FINGERTIPS:



From the Quantum _Universal_Configuration_Guide_:
"Quantum Defines a MB to be 1 x 10^6 Bytes"


QUANTUM LPS120

238766 Sectors, 122MB
=122,248,192 bytes which my software reports as 122 Mb using READ CAPACITY.



RICOH

(512 Bytes x 37 sectors), 2,570 tracks, 48.65 MBYTES
=48,686,080 bytes. (47.7 MB using 2^10 K bytes).



MAXTOR (Tahiti)

Formatted capacities are specified in bytes, not MB.



SEAGATE

Capacities rated in MB but no hard data to verify with and no
definition of MB.
 

IBM

"200 MB" disk reported by my software as 216 MB (using 10^6 for calculation).

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