Difference between IDE and SCSI ??

[Mikkel L. Ellertson]

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 drives 
while PC's were still using MFM and RLL drives, long before IDE 
drives showed up. I could have sworn that SCSI drives pre-dated the 
IBM PC.

Mikkel
-- 

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

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