Re: serial ata

[Aaron Kenney <awkenney@sbcglobal.net>]

    The current SATA controllers are pulling 150MB/sec, not to be 
confused with Mb, which is something else, and really only matters in 
the realm of programming. This is why I've always thought modern network 
speeds should be rated in B not b.
    Typically, like Bryan was getting at, if you monitor the actual 
transfer rate of a serial ATA drive, you will find that they don't put 
out more than 70MB/sec. So they don't even saturate half of the current 
spec. But in real-world application there are quite a few minor benefits 
to SATA that are worth it if you are either building a new computer or 
replacing an old drive. Most noticeably is the sustained transfer, which 
is nuts. Formatting a drive takes a matter of seconds, usually. This is 
faster in Windows than in Linux. I never understood why. Also, 
installing software goes faster. Another example of a sustained 
transfer. I myself wish that the company I worked for had the dough to 
do away with PATA altogether, because as a system builder, SATA can 
shave a serious amount of time off of the process.
    And to answer your other question... max number of drives per 
controller is 16 if your controller has 16 ports. Like Bryan said before 
though, most controllers have 2-4 ports. A 16-port controller will be 
either found in a server motherboard, or on an expansion card. 
Personally, I like the idea of having the controller directly on the 
motherboard, since then the main bus can address the SATA bus directly, 
or at least through a bridge, rather than passing through PCI.
-Aaron Kenney

Bryan J. Smith wrote:

>On Thu, 2005-03-24 at 20:02 -0600, bentley rhodes wrote:
>  
>
>>hey i know i probably asked this already.  but, so what!
>>sata hard drives run at about (but not necesarily AT) 150mb/ sec.
>>    
>>
>
>Er, understand SATA drives run _no_ faster than the same drive mechanics
>but with an ATA or UltraSCSI/320 logic.  The SATA signaling allows upto
>1.5Gbps, approximately 150MBps theoretical at 10/8 encoding.
>
>Most drives today are typically 40-70MBps burst maximum.  Many ATA, SATA
>and even some UltraSCSI drives come off the same line -- depending on
>the manufacturer (see my other posts on this).
>
>  
>
>>i don't see anywhere on tigerdirects web page that say how many devices 
>>you can chain though, per controller.  does anyone know?
>>    
>>
>
>The _official_ ATA DMA specifications dictate that it is a point-to-
>point connection.  That is, 1 end-point controller, 1 end-point device,
>per channel.  There is _no_ "addressing" in ATA.  Now legacy EIDE allows
>the master/slave setup, which was _never_ designed for ATA DMA.  But
>many people use this legacy EIDE compatibility for ATA in violation of
>the specs.
>
>With SerialATA, they have finally enforced it.  Absolutely _no_ slave
>per port.  Now most SerialATA controllers offer 2-4 ports.  But there is
>only 1 device per port, period.  There is a BIOS-ACPI standard called
>Advanced Host Controller Interface (AHCI) that allows intelligent,
>although host (software) driven storage of up to 32-channels/ports.  But
>it's not a hardware controller, just a standard interface for software.
>
>If you want intelligently controlled channels, you want a storage
>controller with an on-board ASIC or microcontroller with SRAM and/or
>SDRAM.  Then you get queuing and other goodies beyond what even SATA
>with NCQ does.
>
>
>  
>


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