Difference between IDE and SCSI ??

Nigel Henry cave.dnb at tiscali.fr
Tue Feb 5 20:21:23 UTC 2008

On Sunday 03 February 2008 15:21, John Summerfield wrote:
> William Case wrote:
> > Hi;
> >
> > Can someone briefly explain to me the difference between an IDE (ATA)
> > and a SCSI device.  After having done due diligence with google searches
> > etc., I am still in a quandary. Nothing I read seems to be consistent.
> > Every time I think I have it figured out, I read a reference that calls
> > for or lists IDE devices that I think should be a SCSI reference and
> > vice versa.  Even going to the various standards sites doesn't clarify
> > it for me.  In fact it makes it more confusing.
> >
> > Therefore, can someone explain, in plain language, how I should use the
> > terms IDE or PATA, and SCSI correctly with regards to a current
> > computer?  What specific attribute of a device or bus does each term
> > apply to?
> SCSI, ATA (sometimes retrospectively PATA) and SATA are technical terms
> that refer to specific technologies, much like christianity, islam and
> hinduism refer to different belief systems.
> SCSI has evolved most incompatibly over time; originally it used a
> 50-pin connector and copper wires, then 68-pin, then there were optical
> versions. Basically they have a fairly decent controller that can drive
> several devices (disk, tape, some printers) concurrently, with little
> loss of perfomance, at least until the bus gets fairly busy. It's often
> configured in hotplug setups, and used in servers and (expensive)
> workstations.
> ATA, sometimes called IDE, started from IBM's PC/AT (from whence the AT)
> with 40-pin connectors, and more recently 40 pins and 80 wires, with
> every second wire grounded. The last incantation is ATA-6.
> A serious limitation is that one device floods the bus; driving a second
> disk at the same time incurs a serious performance penalty - the
> combined performance is scarcely more than the performance of either
> one. that and the fact that (mostly) each interface can only drive one
> device.
> SATA, aka ATA-7, uses smaller data and power cables and uses a serial
> interface. It seems strange (or did to me when serial interfaces
> appeared on mainframes in the late 80s/early 90s), that serial
> interfaces can go faster. I think this is because there's not a lot of
> (long) signal needing to be coordinated, and there's less risk of
> crosstalk.

> John

Sorry for the delay in asking this, but what is the difference between using 
40 pin 40 wire, and 40 pin 80 wire IDE cables?

I ask because on one of my machines I have a fixed harddrive, and also a 
harddrive caddy that uses one of the 5 ¼ slots, and is where I plug my 
various drives in, that have various multiboot installs on them. With a 
standard 80 wire ribbon cable it's impossible to connect both drives, so I 
used the end connector for the fixed data drive, and used an extension cable 
from the middle connector to reach the harddrive caddy. The only extension 
cables I could find were 40 wire ones. I started to notice that there were 
some bootup problems showing up, when booting some distros, so changed the 
cables over, so that the 80 wire end connection was now connected to the 
harddrive caddy that dealt with the OS's, and the 40 wire extension was 
connected to the fixed data drive.

This has resolved the bootup problems I was seeing.

As far as I understand this, an 80 wire cable with alternate wires grounded 
physically separates the wires carrying data, and results in a better data 
transfer to or from the harddrive. Please correct me if I'm wrong here.

I've tried to find 80 wire extension cables without success. Anyone living in 
France know where I can find them?


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