PDA

View Full Version : Sandisk 512MB card query

stduc
29th of October 2003 (Wed), 06:51
I have a Ramstar 512Mb card which is actually 490 Mb and formatted in the camera to 490Mb. I have had it 3 months with no problems. I just got another 512 card (both from scan computers). This turned out to be a Sandisk card and ony 488 MB. I ran a diagnostic check on it before putting it in my A80 and formatting it. The A80 showed it as 488Mb before the format and 487 Mb after the format!
So I am down 3Mb and feeling a bit miffed. Is this trend with 512 card due to continue - where you don't get 512Mb and where did the 1Mb go during the camera's format?

pblevitt
29th of October 2003 (Wed), 07:21
It goes the same way for hard disks.

1Meg (in binary terms) is 1024k which is actually 1024 bits, giving 1048576 bits in a Meg.
Companies say their card is 512Mb in size, which is actually 512 million bits, not megabits.

(Still with me ?)

If you divide your 512 million bits by 1048576 (a proper meg) you get 488.28125 (488Mbit and a bit extra)
When you format the card, you are applying a file system, and that needs somewhere to sit - on your card. If it took up 0.3M, then you would have just less than 488M left. What is left is shown as available space, rounded down, ie 487M.

As an example, you want to make a bookcase on your living room wall. It is 15 feet by 8 feet, giving you a usable space of 120 square feet. You then put up shelves. the amount of usable space is reduce by the thickness of your shelves and supports (your file system).

Not all manufacturers will use the same components, so a slight difference is to be expected.

stduc
29th of October 2003 (Wed), 07:59
Fair enough but wrong! 512 Mb's used to mean 512 * 1024 * 1024. Still that's inflation for you I guess. However .... SEE THIS (http://www.liquidninjas.com/bbs/showthread.php?s=&threadid=5850)

I guess it all depends upon your point of view.

pblevitt
29th of October 2003 (Wed), 14:10
I know and you know that a 'Meg' is 1024*1024 bits, but that is not how the industry sells it's hardware.

If you buy a 120G hard drive, it does not have 30*1024*1024*1024 bits on it, it has 30*1000*1000*1000 - a chunk short of what is advertised.

This is a fact well known in the 'industry' and the link you showed proves it.

Its all to do with marketing

stduc
31st of October 2003 (Fri), 04:48
OK - I know that's how it often is - but it's not how it should be. If you buy a pint of beer you expect a pint of beer not 90% of a pint!

If you buy 512 MB of RAM you get 512 MB, 536870912 bytes (512*1024)

The sandisk card is only 511664128 bytes which is not only 3096576 bytes less than the RamDisk card but 335872 bytes less than a decimal 512MB.

So all I'm, saying is that we are being cheated. In this case by 25206784 bytes - which is not insubstantial.

stopbath
31st of October 2003 (Fri), 10:52
According to the Sandisk web site the 512 card has approximately 512,500,000 bytes (unformatted)
Divide this by megabytes, and you get 488.75808 megabytes (which displays as only 488.)
Since formated the display is at 487, that means the formatting took up more than .75808 megabytes.

Now, since the formated Ramstar had 490 megabytes formated and unformatted, we can assume that when both states were rounded off, the remainder was the same. Now 490 megabytes equates to 513,800,000 bytes. And, if we increase to 490.9 megabytes we get 514,700,000 bytes. So the Ramstar is between 513 and 514 MB, but labled as 512MB. (Given that formatting on the Sandisk took at least .75808 megabyte, the Ramstar disk likely has something around 514.7 million bytes.)

It's not that the Sandisk is short, but the RamDisk had a bonus meg or two.

CyberDyneSystems
31st of October 2003 (Fri), 14:35
Also,. formatting, file allocation and cluster size take up space.... :)

stduc
3rd of November 2003 (Mon), 07:39
I just can't believe the way you guys are defending the manufacturers who are effectively cheating us. At least CANON has the honesty to report 'approx 4 MPixels' for the new A80. (actually 3,871,488 pixels).

I guess you would accept .9 litre and pay for 1 litre of gas? Or buy a 2 litre car that was actually 1850 cc? Or not?

Just because a Megabyte sounds like a Million Bytes doesn't make it so. 1 Megabyte is 1024*1024 bytes by definition.

Now I'm going to let it rest here as I've had enough. Suffice it to say you have all been warned. So, as always, caveat emptor.

stopbath
3rd of November 2003 (Mon), 09:19
Since Million Byte and Mega Byte are so closely named, we need a new naming standard. I propose MB for Million Byte or MegaMyte, and TMB for True MegaMyte. TMB would be correct to the 1024*1024 size calculation, where as MB would be just the byte count.

Thus MB would be the 'metric' style. MB = 1000 KB = 1000 * 1000 Bytes

And TMB would be 'imperial' style TMB = 1024 TKB = 1024 * 1024 Bytes

Naturally, devices (cameras, computers..) would be able to report sizes in your preferred method. Thus comparisons could be apples to apples and oranges to oranges.