On Sat, 2008-02-02 at 15:13 -0600, Mikkel L. Ellertson wrote: > 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 The iBM PC waas released in 1982 with dissk pased PC's shortly after using IDE interface. SCSI was considerably later. -- ======================================================================= I can resist anything but temptation. ======================================================================= Aaron Konstam telephone: (210) 656-0355 e-mail: akonstam@xxxxxxxxxxxxx
