Thread: Info concerning SDcard size and Maximum Tiles

Originally Posted by lolypop000

The class (speed) of the card only indicates its write speed

@Neil

This is wrong...

No it's not. From the offical [Only registered and activated users can see links. ]: 'Speed Class and UHS Speed Class symbols indicate *minimum writing performance to ensure smooth writing of streaming content such as video shooting. This is important mainly for camcorders, video recorders and other devices with video recording capabilities. *Speed Class designates minimum writing performance to record video. The Speed Classes defined by the SD Association are Class 2, 4, 6 and 10.' [*Emphasis added]

Originally Posted by lolypop000

So class 4 is 4Mb/s not always
Look here:

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or

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I didn't say 'class 4 is always 4MB/sec', and anyway that's minimum writing performance. What i said was 'The class (speed) of the card only indicates its write speed, the read speed is the same, class 4-10. As the unit usually does not write to the card but only reads from it, the class is of no importance on the unit. But it sure helps when you are writing large maps to it.' and I stand by that.

As stated, the Class (writing speed) is important in things like camcorders that are WRITING large amounts of data to the cards. Garmin units are not normally writing to the card, just reading from it. In further expanation, of 'The class (speed) of the card only indicates its write speed', this is in regard to the relative write speed i.e. Class 4 is faster than Class 2, 6 is faster than 4, & 10 is faster than 6.

Originally Posted by dasilvarsa

This is what I found from experimenting.
If you use the card in a usb2 internal card reader you get write speeds which are fast (determined by the speed of the card and card reader ).
Im getting 3.6 MB/second write speed ( Windows 7x64 i3 internal card reader usb2)
If you use the card in the Garmin the write speed is determined by the firmware of the Garmin (I'm getting 800Kb/second write on windows 7x64 i3 usb2 nuvi 1300)
The card is Sandisk 4GB Micro SD HC.

I don't think that using a faster card would improve performance in the Nuvi.

The above is also what i have found anacdotally.

Originally Posted by lolypop000

I try on nuvi class2 and in city my map ar stuck or have empty screen for 1 or 2 sec.
Then i buy class 10 and map no more stuck when i drive in city.

p.s.
CN.img was the same on class2 and class10

Flash memory slows in relation to the the total quantity of data that has been written/overwritten onto it, so a lot of reformats and write-cycles will eventually compromise its read speed i suppose. Old cards are maybe slower because the 'wear levelling' capabilities are reduced. That relative read slowness effect you have experienced may be simply more to do with the relative write usage of the cards, rather than as you are thinking due to their class (which is the relative write speed only).

Sorry Loly, i think you have misunderstood me.

A bit more on the relative writing speed of cards in the unit or in a card reader. Early Garmins have a 'USB1' connection capability only, which explains why write speeds are faster using a card reader with USB2 or 3 capability, i.e. the speed bottleneck is caused by the unit's USB write capability. Later units with USB2 capability can be limited by low speed class cards which of course cannot be written to faster than their relative write speed will allow.

USB1.1 write speed is 12 megabit [Mb] per second i.e. 1.5 megabyte [MB] per second [maximum]
USB2 write speed is 480 Mb/s i.e. 60 MB/s [maximum]
USB3 write speed is 5 Gb/s i.e. 625 MB/s [maximum]

SD Class 2 write speed is 2 MB/s [minimum]
SD/SDHC Class 4 write speed is 4 MB/s [minimum]
SDHC Class 6 write speed is 6 MB/s [minimum]
SDHC Class 8 write speed is 8 MB/s [minimum]
SDHC Class 10 write speed is 10 MB/s [minimum]
SDXC [UHS] cards have much higher transfer rates [both read & write in the case of UHS-II, however UHS-I SDXC and Class 10 SDHC probably have same minimum write speed of 10MB/s].

Looking at a couple of examples:

Your nuvi 660 has USB1: You put a 10 MB/s Class 10 SD into it and find it writes no faster than when you had a 2 MB/s Class 2. It can't because it's limited by it's USB1 to 1.5MB/s maximum, therefore not even capable of matching the Class 2 card's 2MB/s minimum write speed. Better to use a USB2/3 card writer which can easily exceed the write speed of any of those card classes, then even Class 2 will write noticeably faster than in the unit.

Your nuvi 3597 has USB2: You put a Class 10 in it and find it writes much faster than with a Class 2 [and relatively faster than with 4, 6 or 8 too]. But when you re-format an SDXC UHS-II [maximum theoretical transfer rate of 312MB/s] to FAT32 and stick that in it can't be written to by the unit at any faster than the USB2 limit of 60MB/s. Maybe better to use a USB3 card writer which has 625MB/s maximum write speed so easily exceeds the 312MB/s theoretical transfer rate of a UHS-II card, but it has a practical minimum write speed of 30MB/s as a UHS-II card anyway, however the card is now acting like an SDHC and so it probably has the minimum write speed of 10MB/s of Class 10 or UHS-I anyway.

It's actually not easy to compare write speeds because the standards vary. USB is given as maximum write speed. SD/SDHC is given as minimum write speed. UHS classes are given as a 'maximum theoretical transfer rate', which I dare say is in fact a read speed and therefore actual write speed is considerably less both 'theoretical' and in real-life. For UHS-I it seems the same as Class 10.

Ok, I have an Etrex 20!

I have 11Gb of Topo maps on the SD card. If I put all the maps in the GARMIN folder then some maps disappear due to the tile limit, ok!

So on the SD card I created another folder called EXTRAS and moved all the non essential map img's there.

As Etrex 20 only sees the Garmin folder, then the other maps are ignored as if they are not there!

But they are still there ready to be swapped between these folders when needed in a flash.

Another folder for extra maps seems to beat the tile limit.

read post n1

What are the file limitations of my outdoor mass storage or MTP device?

September 17, 2015

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Mapping Segments

What is a mapping segment?

September 27, 2011

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What is the largest size memory card supported by my outdoor mass storage or MTP device?

09/28/2015

Many Garmin outdoor mass storage devices include an expandable memory slot. A memory card can be inserted into this slot and used to store the following:

Additional mapping
BirdsEye imagery
Photos (on devices with camera)
GPX files including geocaches, waypoints, routes and tracks
When selecting a memory card, be mindful of the device requirements:

Card form factor (the shape of the card):
microSD card - Most Garmin mass storage devices utilize this form factor
SD Card - Colorado Series*
Card Speed Class (the speed information can be read from or written to the card):
Standard speed class - Most Garmin mass storage devices can use any card with a rating of Class 4 through Class 10
Class 10 and UHS speed class - VIRB, VIRB Elite, VIRB X/XE may experience stutter, pixelation or lag in the video quality when using a card rated below Class 10
Card Size (the amount of storage space on the card):
128 gigabytes (GB) - VIRB X and VIRB XE
64 gigabytes (GB) - VIRB, VIRB Elite and Monterra (card must be formatted to FAT 32 when using with Monterra)
32 gigabytes (GB) - Most Garmin mass storage devices can use cards up to this size
Smaller Cards - Devices will detected cards with as little as 64 megabytes (MB), but few maps will completely load to a card that is this small: Check mapping requirements prior to purchasing a microSD card
Manufacturer (Brand of Card):
While any brand of microSD card should work, Garmin has only tested more common brands such as SanDisk or Kingston.
In addition to the above memory card limitations, there may be other file limitations that apply to your device; for more information reference the FAQ, "What are the file limitations of my outdoor mass storage device?"

* A microSD card can be used with a SD card adapter

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