8/1551 Re: Why Re: Why no third party solutions?

[george@cs.nps.navy.mil (Robert George)]

> >Your're going to take a serious performance hit if you put a hard drive
> >on your serial port.  It would be great for tape backups though.
> 
> Actually, we're (or I) am talking about parallel port hard drives,
> which can reach access times of 12ms or better and decent thoroughput
> under EPP.

You're missing the point.  If you have a hard disk drive with a reasonably
fast throughput you are an order of magnitude faster than the bandwidth of
the parallel port on the ThinkPad.  The acess (average seek) time of the
drive has nothing to do with any of this.  Basically you are going to have
a drive which is sitting around waiting for it's data to be transferred over
a very small bottleneck.

Consider the Sigma Data drives which have a buffer-to-host transfer rate
of 6 _Megabytes_ /sec trying to transfer data over the 960 _Kilobytes_ /sec
of the EPP port.  You essentially have a 600% overhead on all traffic
going to the ThinkPad.

BTW, I'm a little dubious of the transfer rates over a PCMCIA SCSI interface
as well.  The PCMCIA interface operates at 25Mhz, which is plenty fast,
but there's an awful lot of software overhead to get through the socket 
services, card services, card drivers...

Does anyone have any throughput statistics of one of the PCMCIA SCSI cards?

 


| Robert George            |  Army Research Laboratory              |
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