Linked by Thom Holwerda on Fri 19th Oct 2012 20:07 UTC
Windows Interesting little tidbit from the Reddit AMA session with Microsoft's Surface team. One Redditor wondered just how much disk space Windows RT takes up - in other words, if you buy the 32GB Surface RT tablet, how much space is left for your stuff? It turns out that while Windows 8 RT is considerably smaller than its Windows 7 x86 predecessor, it's still huge by mobile standards.
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RE[3]: Not quite true
by tanzam75 on Sat 20th Oct 2012 02:02 UTC in reply to "RE[2]: Not quite true"
tanzam75
Member since:
2011-05-19


So a 120GB SSD does actually have 120GB of storage but you're only allowed to fill ~120GB as the remainer is there purely for load wearing.



That the 7% overprovisioning factor happens to be the same as the difference between GiB and GB is a nice coincidence. But it's just that -- a coincidence.

The coincidence disappears when you look at drives that have RAISE. See, e.g., the 960 GB OWC Mercury Electra MAX 3G SSD: http://www.anandtech.com/show/6038/owc-releases-960gb-mercury-elect...

It has 1024 GiB of raw capacity, and 894 GiB of formatted capacity. The difference is not 7% but 14% -- and it's because some of the raw capacity is reserved for RAISE as well as overprovisioning.

They're advertising this as a 960 GB drive (= 894 GiB), not as a 1024 GB or a 1 TB drive. In other words, they're not advertising the raw capacity in binary prefixes, but the formatted capacity in decimal SI prefixes.

Magnetic hard drives also had a higher raw capacity than formatted, as did floppy disks. Because the difference wasn't anywhere close to the 5% difference between MiB/MB or the 2.4% difference between KiB/KB, the urban legend did not have a chance to spawn as it did with SSDs.

(Trick question: Why are 1.44 MB floppies called that? They're neither 1.44 decimal MB, nor 1.44 binary MiB, nor 1440 decimal KB, nor 1440 binary KiB.)

Edited 2012-10-20 02:15 UTC

Reply Parent Score: 3

RE[4]: Not quite true
by Brendan on Sat 20th Oct 2012 08:55 in reply to "RE[3]: Not quite true"
Brendan Member since:
2005-11-16

Hi,

As far as I know, all magnetic storage manufacturers have always used "dodgy numbers" - a combination of binary and decimal. A "dodgy MB" is 1024*1000 bytes, which is slightly larger than a real MB and slightly smaller than a real MiB. A "dodgy GB" is 1024*1000*1000 bytes, a "dodgy TB" is 1024*1000*1000*1000 bytes, etc.

To add to the confusion, there's "unformatted capacity" (what the magnetic material is capable of), "low level formatted capacity" (what the magnetic material is capable of storing after it's been split up into sectors) and "formatted capacity" (how much free space you're left with after you've put the overhead of a file system on it).

For a simple example; a "1.44 MB" floppy disk has an unformatted capacity of about 2 MB, a "low level formatted" capacity of exactly 1440 KiB, and (depending on which file system you use) this probably drops to about 1300 KiB of free/usable space once a file system is slapped on it.

Of course everything else used for storage (RAM, file sizes, etc) is typically measured in binary sizes (e.g. 8 GiB of RAM); and there are still many morons that use decimal prefixes for binary sizes (e.g. 8 GB of RAM); so it's natural for people to assume a dodgy TB is a binary TiB and wonder why they've been ripped off. In this case the manufacturers like to pretend that file system overhead is the only cause, instead of admitting that their dodgy number scheme is a deliberate scam.

Now; the difference between "dodgy" and "decimal" is constant (e.g. a decimal MB is 2.4% smaller than a dodgy MB, and a decimal PB is 2.4 smaller than a dodgy PB). However, the difference between "dodgy" and "binary" increases with scale (e.g. a dodgy MB is 2.4% smaller than a binary MiB, and a dodgy PB is 9.95% smaller than a binary PiB).

This means that as hard drives get larger, the "dodgy sizes that people naturally assume are a binary sizes" scam grows. For example, by the time we get to yottabytes people will be getting 18% less disk space than they assume they're getting.

The simplest solution is to hunt down these morons that use decimal prefixes for binary sizes and "re-educate them with extreme force". Once people get used to binary sizes they'll start assuming that a dodgy MB is a real MB; and then people will get more disk space than they assumed they would from hard disk manufacturers.

TL;DR: The problem can be solved with violence! ;)

- Brendan

Reply Parent Score: 5

RE[5]: Not quite true
by henderson101 on Mon 22nd Oct 2012 12:05 in reply to "RE[4]: Not quite true"
henderson101 Member since:
2006-05-30

They're not exactly morons. GiB and MiB vs GB and MB is a very, very recent invention. The computer industry always described memory and hard drive storage in terms of Mega/Giga/Kilo- + byte and defined that as 1024 KB (in your world, KiB) = 1MB (again, MiB to you), etc. The Kibi/Mibi/Gibi prefix was invented well after the other standard had been established for over 20 years.

So, basically, the IEC standard prefixed (est circa, 1999) are the "new" kid on the block, versus the old school non SI prefixes (circa ???, but certainly in use from the late 60's, probably earlier.)

Reply Parent Score: 2