Go Back   Steve's Digicams Forums > Digicam Help > Memory Cards, Microdrives, Card Readers

Thread Tools Search this Thread
Old Jul 28, 2006, 12:26 AM   #1
Senior Member
Join Date: Jul 2006
Location: Tumbleweed, Arizona
Posts: 1,381

Here are some answers to the most pressing questions about SD and CD card storage media:

Card Capacity in Number of Images for Sizes in Megapixels

16MB 32MB 64MB 128MB 256MB 512MB 1GB 2GB 4GB
1 Mpixel 32 64 128 256 512 1024 2048 4096 8192
2 Mpixel 16 32 64 128 256 512 1024 2048 4096
3 Mpixel 8 16 32 64 128 256 512 1024 2048
4 Mpixel 6 12 24 48 96 192 384 768 1536
5 Mpixel 4 8 18 36 72 144 288 576 1152
6 Mpixel 0 4 8 16 32 64 128 256 512
7 Mpixel 0 3 6 12 24 48 324 646 1296
8 Mpixel 0 9 18 36 73 146 292 585 1170

Various people are going to look at the table above and say it wrong – my camera gets more or less. There are a number of variables working here, among which are:
  • The make & size of the camera – The specific megapixels of your camera, 3.1 or 3.2 makes a difference. These are approximations. Also the software in the camera can vary in how it stores the images on the storage card.[/*]
  • The make of the card – various manufactures use a slightly different internal structure within the card to store the information, thus there are going to be differences in the specific storage capacities and the cameras.[/*]
  • Powers of 2 – image sizes that are a power of 2; 1, 2, 4, 8, 16 megapixels store more efficiently on the cards, i.e., there is less room wasted at the end of each image when its stored. This is just the way computers and storage works.[/*]
  • JPEG – JPEG is a slightly compressed image format, thus depending on images themselves, there is slight differences in the size each consumes based on how they efficiently each compresses. RAW image counts will vary greatly from these values.
Additional capacity tables are available atCard Performance – Read Write Speed

There are two sites that provide pretty extensive performance test results on CD and SD storage media:Camera Compatibility with various storage card capacities
In order to use drives with a capacity larger than 2GB, the camera must support the use of the FAT32 file system. Most current higher end digital cameras do support FAT32. Older cameras using the older FAT16 standard will be limited to the use of 2GB storage media. Some cameras have a 1GB limit – so you need to check your camera's specifications or call the manufacture. Here are some helpful sites.SDcard to CFcard Converter
Here is a device that lets you use SDcards in a CFcard formatMore informationHope this helps a bit....
interested_observer is offline   Reply With Quote
Sponsored Links
Old Jul 28, 2006, 6:24 AM   #2
Senior Member
E.T's Avatar
Join Date: Jul 2003
Posts: 921

I think that table needs much more than little checking and fixing... for example how 512MB card stores more 8MP pics than 7 MP pics?

Also you can't format card larger than 2GB in camera which doesn't support FAT32 so getting only incomplete capacity into use is quite hard.

And 1GB limit again applies to cameras using SD card, originally size limit was 1GB but it was later tweaked to 2GB which doesn't work with all SD cameras. Also all SD cards over 2GB are SD-HC cards ("high capacity"... sure, limited to 32GB just for fun?) which specially requires support from camera. (plus of course support for FAT32)

Lexar has some kind listing of cameras which support 2GB SD:

PS. CF, not CD.
E.T is offline   Reply With Quote
Old Jul 28, 2006, 9:42 AM   #3
Senior Member
Join Date: Jul 2006
Location: Tumbleweed, Arizona
Posts: 1,381

Here is a little bit more than what you probably ever wanted to know about your SD and CF cards.

Your right, the table can use some tweaking - however some history. Yes- there was a typo CD should be CF. The storage capability of these cards are based on the file structrue used by Microsoft in the early days of the personal computer. The file format FAT12 was used on floppy disks, with FAT16 applied to hard disks and has addressing limitations in the amount of storage that is actually useable using this format. By the way FAT stands for File Allocation Table, with the number indicating the number of bits used in the addressing scheme. I included FAT12 as some of the older cameras might have only expected to use 16MB of storage media. Some of you might remember that as hard drives grew in size and older PC were retro-fitted with newer and larger hard drives that the older PCs were unable to utilize the larger drives full storage potential. The same thing is going on here in the camera storage world. If the camera uses FAT16 and has a larger card inserted it will only be able to address the maximum amount of storage its addressing scheme is capable of (i.e., 1 or 2 GB) others might see a larger amount of available storage and reject the card - it is all in how the software was written.

The maximum size of an individual file in FAT16 is 2 GB. FAT32 is used to address media larger than 2GB in that it has a maximum limitation of 2 Terabytes.

The cameras are essentially embedded computers utilizing the same storage format (licensed from Microsoft) to store the images to. The reason why the numbers are going to vary so much has to do with a number of items. Now I admit that I took an existing table and added to it (for the 6MP, used my Canon SD500 - 7.1MP for an estimate of the 7MP, and cut the 4MP in half for the 8MP).

Here are a few good sites with some background on FATs:
  • http://www.buildorbuy.net/fat.html [/*]
  • http://www.hpcfactor.com/support/cesd/h/0012.asp[/*]
  • http://www.happytech.net/Articles/KenWincel/Fat32Info.htm[/*]
  • http://zdnetasia.com/techguide/storage/0,39045058,39369348,00.htm[/*]
  • http://www.lexar.com/pdf/Lexar_4GB_Fat32.pdf[/*]
  • http://www.imaging-resource.com/PRODS/E20D/E20DA11.HTM[/*]
  • http://www.hitachigst.com/tech/techlib.nsf/techdocs/BB4945CEAAE4DAD986256D890016E8F4/$file/FAT_White_Paper_FINAL.pdf[/*]
  • http://www.smartcomputing.com/editorial/article.asp?article=articles/2005/s1603/36s03/36s03.asp&articleid=25302&guid=[/*]
  • http://experts.about.com/e/f/fi/File_Allocation_Table.htm[/*]

  • [/*]
The reason for wide amounts of variation, as indicated in the first posting is the way the FAT is applied. Simply, think of a SD or CF storage card as a closet filled with shoe boxes of a varing and dynamic sizes ranging from 2K (2048 bytes) to 32K (32,768 bytes) based on the overall size of the media card - the larger the device - the larger the "shoe box" or "cluster". You take a picture - the camera computes the image into a JPEG format thus determining the exact size in bits, then divides by 8 (8 bits to the byte - also this can be more if reliability information is stored) to arrive at the number of bytes that are needed to store the image. Then this number is rounded up to the next cluster size. For instance - lets say that you have a large card that uses cluster sizes of 32Kbytes (or 32K * 8 bits) = 262,144 bits. So if your 1MP camera takes a picture that is exactly 1,048,576 bits, then it will take 4 clusters. 1 more bit, the it will require 5 clusters. Here is a link to a site that provides some background information on this .... http://www.allensmith.net/Storage/HDDlimit/FAT16.htm

Now, in that your pictures are actually computer files using the same storage format as your PC, then they are individually addressable by name. These names take up space on the storage media and the information that actually connects the names to the data making up the actual image. So here is an expirement - take that old card that came with the camera (16 or 32 MB) put it into a large camera (7MP) make sure its empty and take a picture - Say you start out with 9 images - take a picture and you all of a sudden have room for an ESTIMATED 6 pictures left. Take another and all of a sudden you have 2 pictures left. This is the dynamic alloation taking place in that JPEG images based on their compression will vary in size.

Hope that helps....

interested_observer is offline   Reply With Quote
Old Jul 28, 2006, 10:36 AM   #4
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,371


Not a link to a page here in your posts, even though we're a Digital Camera Site, and you're making the posts in the forums here.

How about this page for starters?


BTW, it's also in the Announcement (a.k.a., "Sticky") post at the top of this forums threads list (see the top post titled "Flash Memory Card Info"). ;-)


or, perhaps this one (linked to from the previous page)


or, maybe this one (also linked to from previous pages)


You'll also find lots of links to manufacturers pages for compatibility with memory types in the above articles.

Of course, if you want to find out more about a specific camera's memory requirements, we actually have reviews:


JimC is offline   Reply With Quote
Old Jul 28, 2006, 11:56 AM   #5
Senior Member
Join Date: Jul 2006
Location: Tumbleweed, Arizona
Posts: 1,381

Hi Jim,

I appologize, I did not intend not to link to your surpurb website pages, I just assumed that everyone here, was already familiar with them. I was just trying to amplify on a number of questions I had read in the various postings and to provide some background on why some unexpected occourances happen. Using digital cameras and storage is not like popping down to the local drug store and getting a role of film holding 12 pictures.

You have a wonderful and very informative site here! For the most part my experience with imaging has been not with cameras (well not the type people usually think of, anyway...)
  • Here is a camera everyone can relate to.... (I designed the tracking system for the instrumentation package - i.e., the camera, its only 9.2 meters) - http://www.as.utexas.edu/mcdonald/het/gallery.html[/*]
  • Here is another type of imaging at the other extreme - http://www.sandia.gov/RADAR/images/blackmesa.jpg [/*]
  • Then there is the new availability of overhead imaging brought to the public by google earth [/*]
Next time, I will not go so far a field....

interested_observer is offline   Reply With Quote
Old Jul 28, 2006, 12:12 PM   #6
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,371

I couldn't resist pointing out that a lot of information is here.

It never ceases to amaze me at how often I see posts with links to somewhere else with the same information.

For that matter, every time a new camera is announced, I'll find posts with links to Press Releases on other sites, even when the same Press Releases are usually posted on this site's Breaking News Page .

So, when I see someone posting a lot of links to information elsewhere, I'll sometimes step in and point out that there is already a lot of good information here.

JimC is offline   Reply With Quote

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

All times are GMT -5. The time now is 1:54 PM.