Re: Idea...

[Cyrus Roton <croton@ridgecrest.ca.us>]

On 10 Jun 1995, Todd P. Whitesel wrote:

> 
> SCSI actually allows eight devices -- one per bit of the data bus, which
> is used to assert requests during the arbitration phase. On a standard
> SCSI implementation, the host machine must be counted as a device, hence
> seven other devices may be added.


I think I said eight (zero to seven: that makes eight). I was wrong about 
the three device code lines. Actually, the device number switch, on the 
back of the box, connects one of the lines to any one of the data lines. 
A pulse on that (SEL ??) line is routed to the selected data line for 
return to the host. Never the less, another line would be required if you
wanted more than eight codes. 

> 
> what		bits	Mhz	speed
> ----		----	---	-----
> Apple bus	8	1	1.00 MB/s
> Ethernet	1	10	1.25 MB/s
> 
> Who's losing speed?
> 
By "MB/s" do you mean bits/sec or bytes/sec? With serial data flow 100,000 
Kilo Bytes per sec equates to 1 Meg Bits per sec. (assuming one start 
bit, eight data bits, one stop bit).

What I said about speed loss is sometimes true: If you convert parallel 
data to serial data, the speed is cut to one tenth (approx), assuming 
that the output clock is the same speed as the input clock. I failed to 
recognize that the converter may output data with a higher clock rate than 
that on the parallel input side. There are cases where the data 
throughput rate on the network is faster than the ability of the 
individual computer to supply it.

Thanks for the corrections. Nobody is perfect (especially not I), but, we 
can learn from our mistakes.

Cy Roton