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In Reply to: RE: with the data going over the SATA cable to RAM posted by Tony Lauck on July 11, 2014 at 07:11:38
... from the point of view of interaction with the rest of the system. The fact that no music data is being read or written, doesn't mean there's no activity - at the very least, there's OS monitoring the hardware's health.In other words, I'm sure SATA cable will affect the SQ, even if file is fully loaded into memory before playback - but mechanism is NOT that of data being "screwed up", passing through the cable before loading.
Edits: 07/11/14Follow Ups:
Do you have any information as to how often and/or how much "health" or "keep alive" interaction goes over SATA cables in Windows operating systems? I suspect this may depend on how the BIOS and OS have been set up.
There isn't a lot of traffic to/from the disks. The disk I/O light on the PC flashes all the time when I play music off the hard drive, but it rarely flashes while playing music out of the RAM disk. The O/S seldom goes to disk as most of its activity seems to come out of cached RAM.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
"The O/S seldom goes to disk as most of its activity seems to come out of cached RAM."
Besides, if your OS disk is separate from your external disk holding your music library, any non-cached OS interactions will be to your internal disk which should not have a long exposed SATA cable outside the shielded computer enclosure.
As an aside, with the Mac Mini or the PC, if I use an external disk for my music library, I can unplug it while music is playing out of RAM. There is no 'activity' to the disk at this point. How could there be, it's unplugged!
Not sure about Windows but you'll find very little OS activity 'chattering' to disk in UNIX based OS's like Mac OS. That's why, in the old days anyway, one would run the UNIX 'sync' command to flush (RAM) cache to HDD before invoking the 'init 0' forced shut-down.
From the Terminal screen on my Mac
If I run the OS off the Mac Mini internal SSD (as I normally do), and the music library off the Mac Mini internal HDD, there are no SATA cables involved. Both disks are direct attached via very short flex circuit header, and tightly shielded within the machined aluminum casing.
I don't have any powered up external drives. All my active drives are inside my PC case. I think it is a mistake to do otherwise. I do have an E-SATA header and cable that goes to a Blac-X box. The Blac-X provides a slot that accepts SATA data and power connectors and allows me to use "naked" SATA hard drives for external backup. This device is used once a month or so for off-site backups. I suppose that the idle SATA cable from my PC case to the Blac-X box is somewhat degrading my sound, but I doubt the sonic benefits are sufficient to justify grovelling in the dust on the floor while doing the requisite extensive listening tests. (Life is too short to spend time trying all possible tweaks. So I haven't tried testing the effect of tying bowlines, grannies and square knots in the window blind shades.)
Windows drives can be configured to flush or not flush the cache. I normally set them to do lazy writes, which means they may take some number of seconds before data gets written to the drive. For my E-SATA drive I have an add-on utility program that allows me to safely remove this drive, even though Windows thinks this drive is purely internal. Plus, the Blac-X box has some rather garish lights to indicate on-going I/O activity. Of course this paranoia is completely inapplicable for drives that are "read-only".
I looked at the SATA spec. The drivers are floating when no frames are being transmitted. I suspect that an idle SATA data cable causes most of its interference through the ground wires, so I am not sure how shielding is going to help. Also, there aren't going to be any data errors passed on, just dropped frames due to bad (32 bit) CRC's. I do have no doubt that an active SATA cable could radiate all kinds of noise that might affect other equipment (that shouldn't be sensitive to the interference).
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
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