Questions about SD memory cards

[Indiana_Tom]

Hi all,

First of all, thanks very much for making this forum.  I am a new GPS user and have a Garmin Dakota 20.

This is my first post and it involves SD memory chips.  Is one type or size considered better than another or are they generally the same?

Would a particular size SD card be preferred?

Correct me if I am wrong but it would seem to me to be better to have several smaller SD memory cards rather than one bigger one.  My theory is if you develop a problem, it is less likely to affect everything.

And last but not least is it advisable to leave the Dakota 20 unit memory alone with just the baseman in memory and add all other downloaded maps to an SD Chip?

Sorry for the multiple questions but I figured it would be better to get all of them out at once.

[maps4gps]

Welcome

First - backup the files on the DK20 to your computer.

I have not heard of any brand to stay away from; however, I would go with a SandDisk.
A test by a poster on groundspeak.com found a very slight speed improvement of a class
6 card over a class 4;  no additional speed increase with a class 10 card.

Size depends on how much you are going to put on it.  A 24k IN topo would be around 100Mb.  The same area with Garmin's 24k topo including the 3D elevation data might be 300?Mb.  Garmin's birdseye imagery would be many times more for even a moderate sized area.

One or many cards is probably more your preference.  The more data on a card, the longer the startup time.  Changing cards at home is OK, outdoors in the wind and one of the cards may blow away.

If the map data is on a card and something goes wrong, the card can be remove and the GPSr will usually start. 

[eaparks]

Personally, I prefer to stay with the larger name brands such as SanDisk or Kingston.  The reason I say this is because I've used more than 50 of their cards and so far I havn't had a single defective memory card over a 7 year period.  I did have a defective SanDisk SD adapter once.  I have read on various forums where other posters do occassionally have a problem with some of the lesser known brands.  For the small difference in cost between a SanDisk or Kingston and the cheapest cards it just isn't worth the risk to me of having a card go bad at an inopportune time.

I generally order through Amazon but you do need to be careful with some online vendors.  I ordered 3 new 8Gb micro SD cards thru Amazon from a vendor in CA; all 3 cards were ordered together and all 3 had been used and had someone's pictures taken in a foreign country (not the U.S.), their ringtones, and their songs, on all 3 of the cards.  With any new card always do a full format (Fat 32 format) before using it.

edit:  The majority of problems that most users experience with memory cards is either the card not being locked or inserted properly into the GPS or a corrupt .gpx file.

[maps4gps]

Just purchased a SanDisk 32Gb class 10 micro card for $29.95 from this week's BestBuy sale.

For an 8Gb vector datamapset on a 8Gb class 4 SanDisk micro card: 
  Initial 'start-up' = 80 seconds;  later start-ups = 41 seconds
32Gb class 10 SanDisk micro card:
  Initial 'start-up' = 47 seconds;  later start-ups = 15 seconds

A seamless 24k scale 48 State topo mapset may be more usable than it orginally seamed.

[Boyd]

Thanks for posting, that's interesting. I have a class 10 16GB card with over 14GB of birdseye imagery on it. Startup time is painfully long, never timed but it was probably about a minute. I am just too impatient for that, especially when a firmware glitch shuts down the device while navigating and you want to get back up and running as quickly as possible.

Personally, I leave the card slot empty on my Montana unless I have a specific need for the day, like Birdseye or my pre-loaded 24k Garmin topo card. But the Montana has 4GB internal memory, so that helps.

Curious about the "initial startup" vs "later startup". What do you think is happening there? I don't think the GPS writes any data to the card, so maybe it builds some kind of index in its own protected memory? But why wouldn't it remember that when you switched to the 32gb card, since you used the same map before on the 8GB card?

[popej]

GPS scans maps which are loaded first time at least to check copy protection. Then it remembers maps even if you swap cards. I think one of factors triggering rescan is creation date inside img. Maybe file save date is considered too, this would explain rescan after copying.

[maps4gps]

It appears to me that on power-on, the OR300 checks for mapsets (etc. ?).

If there were no changes since it was last used; start-up is fairly rapid (with class 10).

If there is some change to the mapsets (addition or deletion), there are a series of progress bars and it takes much longer for the OR300 to be ready to display the map.  On the 8Gb data set (loaded as two 4Gb half-mapsets) it went through 4 progress bars.  Probably one for each half of the mapset, one for the built-in world map, and one for (tracks, waypoints and/or ??).  The GPSr is probably building an index of the bounding coordinates for each of the .img files.