[Coco] CoCoSDC performance issue - can someone try this from OS-9?

[Allen Huffman]

> On Feb 1, 2015, at 2:29 AM, Nick Marentes <nickma2 at optusnet.com.au> wrote:
> 
> You realize that defrag does little speed-wise on any memory based drive?

> There is no head seek on these, they just access the next block instantly just like normal memory.


True, seek time is not an issue, but the amount of I/O that has to be read is. The SD card isn’t being accessed just like normal memory — it’s bringing it in a byte (or word) at a time serially.

On the CoCo. reading from a hard drive or SD card is pretty much maxed out — the devices are so much faster, you aren’t getting the data any sooner either way... But, the number of sectors you have to read to piece together that file adds up. If the CoCo had enough RAM to keep the 64K FAT in memory, and cache the segment list (that part it possibly does, it fits in a sector), then it wouldn’t be a huge issue.

Also — There’s a difference between defrag and optimize.

In my case, if I had a 720K file that had 18 segments (which I did), each segment would require going back and reading another ID sector to parse, so that’s 18 sector reads that cold be avoided. That’s where a quick file defrag comes in handy.

Optimizing can put all the used sectors near each other and cut down on all the holes in the disk. That way, when it goes to expand a file, or write a new one, it doesn’t have to seek through a FAT looking for a bunch of little spots to put it. That’s where mine was getting bogged down.

Modern operating systems, like Mac OS X, do their own defragmenting — but it’s really not new or modern. The Mac OS X approach is to always write files out as one chunk. OS-9 has had that capability forever, but it wasn’t very practical on a floppy drive. I have read mixed articles on whether or not Mac OS X ever defrags files in the background. Maybe it does, but so does my Work PC (well, not in the background, but every night at 2am when the defrag program kicks off).
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