Fedora Users — Re: Difference between IDE and SCSI ??

Les wrote:

Hi, Bill,
	IDE was one of the early standards.  It evolved way early in the
progress of computers:
1985: Control Data, Compaq Computer, and Western Digital collaborate to
develop the 40-pin IDE interface. IDE stands for Intelligent Drive
Electronics, more commonly known as Integrated Drive Electronics.
(http://pcworld.about.com/news/Sep132006id127105.htm)

	This was the first attempt to standardize the interface between mass
storage and computer systems.  Actually, though, a similar interface was
developed by several different companies around the 1978 timeframe.  I
owned a Northstar single density hard-sectored 5.25" disk system for my
Altair 8080B that used a similar connector and controller around 1979.

I still have it by the way.

	Basically the disks had little electronics on them.  But they needed to
move the head to different tracks, keep track of the disk position,
write data to the disk, read data from the disk, change the data from a
serial stream to a parallel word, and pass that word back to the
computer.  The IDE standard established the number of bits required to
perform these functions, a means to establish which disk to boot from
and a method to perform the dat transfer, along with all the stuff
needed to control disk speed, sector count, and buffer the data.

There was a half step between IDE and SCSI called ESDI.  The design of
the original IDE had some size limitation that prevented disks from
growing to meet demands.  I don't know too much about it any more, but I
did work on some systems that had it:

1985: Western Digital produces the first ESDI (Enhanced Small Device
Interface) controller board, which allows larger capacity and faster
hard drives to be used in PCs.
(http://pcworld.about.com/news/Sep132006id127105.htm)

SCSI was developed to address shortcomings in ESDI and add multiple
drive capability.  I don't know for sure the drive count limitation on
SCSI, but I believe it was 7 or 15 originally, due to addressing bit

size.

1986: The official SCSI spec is released; Apple Computer's Mac Plus is
one of the first computers to use it.
(http://pcworld.about.com/news/Sep132006id127105.htm)

	SCSI is a serial system, or at least it can be.  It allows virtually
unlimited storage size, and has been implemented as a mother board in
several systems, where the drives plug directly into the frame.  In
these cases the mother board also forms the means to permit hotplug, by
establishing the mechanical order of contact and the buffering of the
pins from spiking.

	SCSI was originally deployed by apple as noted in the article, but also
in commercial applications.  Sun Systems almost exclusively used SCSI
due to speed and capacity needed for their workstations.  Also the SCSI
bus system was ideal for server systems where large quantities of data

had to be stored and quickly retrieved.

The standards for both are posted in the IEEE and ACM websites, along
with lots of good papers on the processes.  Look between the years 1979
and 1985 if you are interested in the evolutionary history of the two
systems (and ESDI).

Regards,
Les H

Are you sure about your time line? I can remember using SCSI driveswhile PC's were still using MFM and RLL drives, long before IDEdrives showed up. I could have sworn that SCSI drives pre-dated theIBM PC.


Mikkel
--

  Do not meddle in the affairs of dragons,
for thou art crunchy and taste good with Ketchup!

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