Post Reply 
HP 50g & SD Cards: Performance, Format, Notes
07-21-2016, 12:57 PM
Post: #27
RE: HP 50g & SD Cards: Performance, Format, Notes
(07-21-2016 12:07 AM)JDW Wrote:  Joe Horn,

Thank you for the detailed comparison! Fascinating to see that CLUSTER SIZE and CLUSTER QUANTITY doesn't matter one little bit. (So much conflicting info in this thread! Ack!)

But of course, we all want to know the single most important detail that you did not specify:

What's speed rating of that INX 1GB card that won the race? :-)

It's not so conflicting, let's clarify a bit.
What becomes slower with cluster quantity is ON time, the time between pressing the ON key and getting the stack ready to work. This is because during ON, the card free space is calculated, and it needs to read the entire FAT table for that. More clusters means larger table. Also FAT32 tables are twice the size of FAT16 tables with the same number of clusters.
Joe didn't measure ON time unfortunately. Cluster size does affect speed, but the test above only wrote 2 relatively large files, so it doesn't matter. Now if you run a test using many STO commands for small objects, it's one cluster per object. So a 32k cluster is writing 8 times more data than a 4k cluster, therefore it's 8 times faster. In Joe's test, the 40k file would write 64k or 40k, only 60% more data. The 200k file would only be 12% more data. That's why you don't see a big performance hit.

Speed rating of the card doesn't matter once the card is rated above 2MB/s. Only very old cards wouldn't reach that.
Egan did a good SD card performance analysis way back then:

As you can see, "modern" (Egan wrote that probably around 2008/2009, he can correct me if I'm wrong, hence the quotes on modern) 1GB and 2GB cards perform well, same as shown on Joe's tests. Only older cards are bad and also had compatibility problems on many of them.
Bear in mind Egan's tests were done using libfsystem from hpgcc, which is way faster than the 50g OS, so the cards are showing more of their "true" performance. libfsystem clocks the cards faster and uses the high speed mode, so it can theoretically transfer up to 10 MB/s. In practice you'll see cards around the 2MB/s mark (with file system + protocol overheads, copying buffers, etc. you won't get the max speed even if the card can do it).
Find all posts by this user
Quote this message in a reply
Post Reply 

Messages In This Thread
RE: HP 50g & SD Cards: Performance, Format, Notes - Claudio L. - 07-21-2016 12:57 PM

User(s) browsing this thread: 1 Guest(s)