[mythtv-users] OT: Size (MB) of Samsung HD501LJ drive?

Michael T. Dean mtdean at thirdcontact.com
Tue Oct 9 04:56:47 UTC 2007


On 10/08/2007 11:12 PM, Jay R. Ashworth wrote:
> On Mon, Oct 08, 2007 at 04:32:29PM -0700, David Brodbeck wrote:
>   
>> On Oct 8, 2007, at 4:27 PM, MythTV wrote:
>>     
>>> Mine are all in a hardware raid 6, but they show up under the 3ware  
>>> raid
>>> tool as:
>>>
>>> SAMSUNG HD501LJ 465.76 GB
>>>
>>> I was a little surprised when I bought them that there was 35 gig
>>> missing from what I was expecting.
>>>       
>> Probably they're using the "1 megabyte = 1 million bytes" convention.
>>
>> 465.76 * 1024 * 1024 = 488,384,758
>>
>> Probably rounds to 500,000,000 bytes if you look at it before  
>> formatting, with a salesman's eyes, and squint a bit.
>>     
> Sales people sell megabytes, engineers measure in gibibytes.
>
> Since megabytes are smaller, there are more of them.
>
> Additionally, they're probably selling unformatted capacity.
>
> Now *I* didn't think that redefining the megabyte to make hard drive
> sellers happy was a Good Idea, but no one asked me.

But kilometers were 1,000 meters; megajoules were 1,000,000 joules; and,
gigawatts were 1,000,000,000 watts (and, interestingly enough, were
typically pronounced "jigawatts"--just like Christopher Lloyd did in
Back to the Future) before computers were here.

It was the computer engineers that tried to redefine these standard SI
prefixes to have meanings that worked well in the base-2 world of
computers.  And then there were those "math-challenged" computer
engineers that used a "truncation-based" approach to prefixes (i.e.
1,374bytes = 1.3kB or 1kB and 1,286,9005 = 1.2MB or 1MB).  Now *I*
didn't think that redefining the mega prefix to make computer engineers
happy was a Good Idea, but no one asked me.  ;)

Besides, now we have the crazy world of computers where standard
prefixes have become meaningless because of the confusion caused by this
attempted coup on meaning.

When describing bitrates, binary prefixes are almost never used, so
6Mbps max bitrate should mean 6,000,000 bits per second and 100Mbps fast
ethernet should mean 100,000,000 bits per second (yeah, ignoring the
real vs theoretical transfer speed).  The only time you're likely to see
a binary prefix used is when talking about bytes per second ("My browser
shows an average transfer speed of 80kB/sec.") and almost always from
someone who's not familiar with the technology (perhaps "not intimately
familiar" is a better description).

When describing bandwidth of buses, decimal prefixes are used.  So,
DDR2-400 memory has a 3.2GB/sec transfer rate because it runs on a
double-pumped 200MHz bus, transfering 200,000,000 cycles/sec × 2
transfers/cycle × 8 bytes/transfer = 3,200,000,000 bytes/sec.

When describing storage:
 - HDD's manufacturers specify capacity using decimal prefixes
 - CD capacities are always given using binary prefixes (a "700MB" CD
holds 700MiB--though possibly not exactly as exact capacity is partially
determined by the writer)
 - DVD capacities are always given using decimal prefixes:  a "4.7GB"
DVD holds 4,700,000,000 bytes
 - System memory manufacturers specify capacity using binary prefixes
 - USB flash drive manufacturers specify capacity as power-of-two
multiples of decimal megabytes (i.e. 256MB flash drive is 256,000,000 bytes)
 - The 1440kiB 3 1/2 inch high-density floppy drives held 2 times the
data of the original 720kiB IBM PC 3 1/2 inch diskettes, but
manufacturers wanted to make it sound more impressive, so they called
them 1.44MB drives--in fact, 1440kiB is 1.40625MiB or 1.47456MB, so it
fits neither the binary nor the decimal prefixes (manufacturers used
decimal kilo times binary kibi to get the 1.44MB:  1.44 * 1000 * 1024 =
1474560 bytes)

So, basically, the "standard" prefixes (kilo, mega, giga, ...) mean
absolutely nothing and clarification is almost always necessary.  Even
when talking about bitrates or bus bandwidth, the listener/reader
doesn't know whether the speaker/writer knows that bitrate/bandwidth
should always be given using decimal prefixes.

However, the binary prefixes /always/ have a binary meaning, and if you
use them, your words have only one meaning.  I'm not saying to use
binary prefixes with a very strange number to describe a bitrate (i.e.
"I set the max bitrate for my PVR-150 to 5.722Mib/sec"), but when
talking about storage capacity or file size or something that /is/
typically measured in powers of two, using a binary prefix indicates you
mean what you say.  Though most people will look at you funny when you
say, "My HDTV recordings average 3.5 to 8 gibibytes per hour," it has
only one meaning, but saying, "My HDTV recordings average 3.75 to 8.6
gigabytes per hour," can be interpreted in either of 3 ways (decimal
prefix, binary prefix, or truncation).

Don't hate the hard drive manufacturer.  Hate the industry.

Mike "binary prefixes yobi used more often" Dean


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