Crosswords0 min ago
SDHC memory card capacities?
4 Answers
Why is it that my 16GB SDHC memory card can only actually hold something like 14.8GB of stuff. 1.2GB is quite a lot of memory so why is it not called a 15GB card? I've noticed the same on 8GB cards etc.
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All answered here, due to constraints of SD card file systems
http://en.wikipedia.org/wiki/Secure_Digital
http://en.wikipedia.org/wiki/Secure_Digital
Part of the problem is the way data on computers measured.
For example you would expect a kilobyte to be 1,000 bytes but it is actually 1,024 bytes. So this rounding down loses 24 bytes.
So when you get to talking about megabytes and gigabytes then this 24 bytes becomes a large number.
So when a memory card maker talks about 16gb or a hard disk talks about 500gb then those sizes have been rounded down to ignore those lots and lots of 24 bytes.
So a 16gb memory card is never going to hold 16gb of data and a 500gb hard drive is never going to hold 500gb of data.
For example you would expect a kilobyte to be 1,000 bytes but it is actually 1,024 bytes. So this rounding down loses 24 bytes.
So when you get to talking about megabytes and gigabytes then this 24 bytes becomes a large number.
So when a memory card maker talks about 16gb or a hard disk talks about 500gb then those sizes have been rounded down to ignore those lots and lots of 24 bytes.
So a 16gb memory card is never going to hold 16gb of data and a 500gb hard drive is never going to hold 500gb of data.
It isn't a matter of rounding down. There are two different multipliers in user.
Historically the SI multiplier kilo (10^3) was misused to describe 1024 (2^10) bytes. This misuse continued with Mega and Giga.
Disk manufacturers rightly rated their equipment in Gigabytes (10^9) while Microsoft uses the binary multiplier system.
The binary multipliers of bytes are designated by the SI system as kibibyte, mibibyte and gibibyte. They are supposed to be abbreviated to KiB, MiB and GiB but this has not caught on.
Historically the SI multiplier kilo (10^3) was misused to describe 1024 (2^10) bytes. This misuse continued with Mega and Giga.
Disk manufacturers rightly rated their equipment in Gigabytes (10^9) while Microsoft uses the binary multiplier system.
The binary multipliers of bytes are designated by the SI system as kibibyte, mibibyte and gibibyte. They are supposed to be abbreviated to KiB, MiB and GiB but this has not caught on.
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