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Old 02-03-2008, 08:18 PM
Alan Cox
 
Default Difference between IDE and SCSI ??

> > The iBM PC waas released in 1982 with dissk pased PC's shortly after
> > using IDE interface. SCSI was considerably later.

SCSI has a whole history prior to the PC world adopting it (and originally
was known as SASI)

> the AT Attachment interface didn't arrive until the PC/AT.

Somewhat later than that. PC/AT was ST-412. The first 'AT attachment'
type interfaces were some of the 'hardcard' devices and then a few PC
systems had various pre-ATA standard interfaces based on routing ISA
timing (aka PIO 0) I/O cycles direct to a controller on the disc and
replacing the PC side controller with a simple address decoder and glue
logic to route the right I/O cycles.

> The PC didn't (originally) have disk at all, the PC/XT was the first
> with disk, and it used the ST-506 interface.

Alan

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Old 02-03-2008, 08:20 PM
Alan Cox
 
Default Difference between IDE and SCSI ??

> There was also EIDE.

EIDE, IDE, Fast-ATA and similar names are all essentially marketing names
for the same ATA interface.

> > in commercial applications. Sun Systems almost exclusively used SCSI

No - older Sun systems used Xylogics interfaces.

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Old 02-03-2008, 08:35 PM
Alan Cox
 
Default Difference between IDE and SCSI ??

On Sun, 03 Feb 2008 13:54:26 +1030
Tim <ignored_mailbox@yahoo.com.au> wrote:

> On Sat, 2008-02-02 at 11:57 -0800, Les wrote:
> > SCSI is a serial system, or at least it can be.
>
> Pardon? Usually, when one has a data bus for several parallel data
> lines at once, one refers to it as parallel.
>
> Serial - one data line, that sends bits sequentially.
> Parallel - several data lines, that send bits simultaneously.

Of course its never that simple. Most "serial" busses are actually
multiple wires which send information in parallel..

And nowdays a lot of devices have multiple serial interfaces that are not
clock synchronous with each other to get higher bit rates than parallel
can do.

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Old 02-03-2008, 10:26 PM
Les
 
Default Difference between IDE and SCSI ??

On Sun, 2008-02-03 at 21:20 +0000, Alan Cox wrote:
> > There was also EIDE.
>
> EIDE, IDE, Fast-ATA and similar names are all essentially marketing names
> for the same ATA interface.
>
> > > in commercial applications. Sun Systems almost exclusively used SCSI
>
> No - older Sun systems used Xylogics interfaces.
>
I guess I should have added a date to that statement.... Absolutes will
get you every time. My personal experience with Sun dated from about
1990, and the systems I opened up had only SCSI in them.

Regards,
Les H

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Old 02-03-2008, 10:32 PM
"Kevin J. Cummings"
 
Default Difference between IDE and SCSI ??

Les wrote:
> On Sun, 2008-02-03 at 21:20 +0000, Alan Cox wrote:
>>> There was also EIDE.
>> EIDE, IDE, Fast-ATA and similar names are all essentially marketing names
>> for the same ATA interface.
>>
>>>> in commercial applications. Sun Systems almost exclusively used SCSI
>> No - older Sun systems used Xylogics interfaces.
>>
> I guess I should have added a date to that statement.... Absolutes will
> get you every time. My personal experience with Sun dated from about
> 1990, and the systems I opened up had only SCSI in them.

Sun servers from that time frame could be used with Xylogics controllers
to talk to SMB disks. Most of the workstations had external SCSI ports
and you could buy external disks to hang on your external SCSI cable chain.

> Regards,
> Les H
>


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Old 02-04-2008, 07:00 AM
John Summerfield
 
Default Difference between IDE and SCSI ??

Alan Cox wrote:

On Sun, 03 Feb 2008 13:54:26 +1030
Tim <ignored_mailbox@yahoo.com.au> wrote:


On Sat, 2008-02-02 at 11:57 -0800, Les wrote:

SCSI is a serial system, or at least it can be.

Pardon? Usually, when one has a data bus for several parallel data
lines at once, one refers to it as parallel.

Serial - one data line, that sends bits sequentially.
Parallel - several data lines, that send bits simultaneously.


Of course its never that simple. Most "serial" busses are actually
multiple wires which send information in parallel..


More likely
txdata
rxdata
Maybe a pair for the other direction (eg RS0232C)
Ground

For a modern cable that has fair throughput, view your ethernet cable:
http://www.ertyu.org/steven_nikkel/ethernetcables.html







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John

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Old 02-04-2008, 08:46 AM
Tim
 
Default Difference between IDE and SCSI ??

On Sun, 2008-02-03 at 23:46 +0900, John Summerfield wrote:
> The PC didn't (originally) have disk at all, the PC/XT was the first
> with disk, and it used the ST-506 interface.

Is that the XT disc, or yet another scheme? I still have an XT drive or
two in a box, and the large MFM drives with two ribbon cable interfaces.
I think they're all MASSIVE 10 megabytes each. ;-)

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2.6.23.12-52.fc7 i686 i386

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Old 02-04-2008, 08:47 AM
Tim
 
Default Difference between IDE and SCSI ??

On Sun, 2008-02-03 at 23:21 +0900, John Summerfield wrote:
> 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.

After years of using parallel buses, because they *were* faster, it does
seem to go against the grain. But what you said is the reason.
Previously parallel buses were faster simply because of the lack of
speed in the, then, current serial circuitry. If you could get faster,
and accurate electronics, which you *now* can, serial can manage faster
rates, easier and more reliably.

As I recall, mainframes had very high speed serial data connections, a
long time before PCs had them. But then personal computers are a
completely different kettle of fish.

> ATAPI is a sort of cross between SCSI and ATA, It used ATA wiring and
> electronics, and some SCSI commands. Mostly used for optical drives,
> but also (I think) for tape drives.

It was also used in Zip and LS120 drives.

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2.6.23.12-52.fc7 i686 i386

Don't send private replies to my address, the mailbox is ignored.
I read messages from the public lists.


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Old 02-04-2008, 10:28 AM
Alan Cox
 
Default Difference between IDE and SCSI ??

> > Of course its never that simple. Most "serial" busses are actually
> > multiple wires which send information in parallel..
>
> More likely
> txdata
> rxdata
> Maybe a pair for the other direction (eg RS0232C)
> Ground

Actually RS232 has a whole array of wires sending information in parallel
(think carrier, flow control, data in, data out, ...). Ethernet has a lot
less but is only 1GBit. Internal busses like PCIE use multiple data links
but are not parallel in the 'traditional' clocked sense

Alan

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Old 02-04-2008, 10:39 AM
Alan Cox
 
Default Difference between IDE and SCSI ??

> speed in the, then, current serial circuitry. If you could get faster,
> and accurate electronics, which you *now* can, serial can manage faster
> rates, easier and more reliably.

No.

The reason is quite different. When you have a parallel cable all the
wires are never quite the same length, diameter or metal properties
(ditto tracks on a board). That means that the signals arrive at the ends
of each wire at different times. Your clock rate is thus limited by the
cable quality and length as well as these propogation delays. That is
what limits PATA to UDMA/133. Any faster and the bits just won't turn up
on time.

If you have one or more serial links with their own clock the clock
arrives with the data on that link as it does for example with ethernet.

Alan

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