Prospect said:
Why can't they make a 210GB that you are able to get all 200GB out of it?
Its all about marketing vs engineering. Looking at the outside of my Maxtor HDD, the blurb says "A gigabyte (GB) means 1 billion bytes".
From an engineering perspective ...
1 bit = 1 bit
1 byte = 8 bits
1 kilobyte (KB) = 2^10 bytes = 1024 bytes
1 megabyte (MB) = 2^20 bytes = 1024 KB = 1048576 bytes
1 gigabyte (GB) = 2^30 bytes = 1024 MB = 1048576 KB = 1073741824 bytes
Engineers are using the fact that the basic memory storage unit is binary - and not decimal - when they build this progression.
Marketing people say "sh*t this is too hard, lets stick to decimal. People know decimal, and it will make the number look better. Another latte Brendan?" so their perspective is ...
1 bit = huh? like "my dog bit me?"
1 byte = ummm ... like "take a bite from this apple?"
1 kilobyte (KB) = 10^3 bytes = 1000 bytes
1 megabyte (MB) = 10^6 bytes = 1000 KB = 1000000 bytes
1 gigabyte (GB) = 10^9 bytes = 1000 MB = 1000000 KB = 1000000000 bytes
So, a marketing GB is actually 93% the size of an engineering GB ...
The big problem is that computers, and computer software, are designed by engineers that know what a bit, byte, megabyte, etc REALLY are, so thats what they report ... and all of a sudden the drive you bought that the marketing people told you was 200GB, is actually only 93% of that - or 186GB. There have been class action lawsuits over this marketing practice, which is why the manufacturers now put "their" definition of what a GB is on the side of the box (even if it is wrong).
Engineers aren't perfect either - they mess up the correct use of k for kilo and use K instead. Their excuse is that K refers to the decimal version used by marketing people (good to have someone else to blame).
So, will a 200GB drive hold 200GB of files? As pointed out there are overheads for partitioning, but a bigger killer is sector/block sizes. Each "chunk" of a file takes up a block (the smallest referencable unit on a HDD) on the hdd. So if you are set up so that your HDD has 8k blocks, if you store a 1k file on there, it only occupies 1/8 of the available space, and the rest of the space is unusable by anyone else.
Oh yeah - and the 8MB buffer thing? That is a chip on the controller board of the HDD, it has nothing to do with using space on the HDD - it means that data will read/write to the buffer area - sort of like filling a bucket with a hole in it. You can dump water quickly into the bucket (ie memory read/write fast), but the hole will only drain at a constant speed (write access time to the HDD).
Sorry for the rant. Its right up there with the megahertz myth in marketing.
np