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Old December 18th 17, 11:15 AM posted to microsoft.public.win98.gen_discussion,microsoft.public.windowsxp.general
Paul[_6_]
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Posts: 41
Default New HDD, has corrupted Data - AGAIN

wrote:

I have no problem with SATA drives. I dont think they would work for
Win98 though. One thing about them, I dont understand why the data cable
has so few wires compared to the IDE cables, and even more puzzling why
the power connectors have all those pins, when there is still only 5V
12V and a copule grounds needed (4 wires). Why do they have all them
pins? Why didnt they just use the common 4 pin connecters they have used
for years. All that did is make power supplies more complicated and the
need to buy adapters to use older power supplies.


The SATA 7 pin data uses TX+,TX-,RX+,RX-,
and those are differential serial connections.

The data travels serially, a bit at a time, like a modem.
Only it happens at 6Gbit/sec, which is "faster than your microwave oven".
It's a signal at microwave frequencies.

So that's how they squeezed down the data cable, by going serial.

USB uses this approach too. USB3 uses TX+,TX-,RX+,RX- .

This document is 3.6MB and it has a picture of what the
SATA data signal looks like, at 6Gbit/sec. And it isn't
even an eye diagram picture - the picture is standalone
ones and zeros. Page 4 has the picture.

http://download.tek.com/datasheet/4HW_19377_15_0.pdf

*******

The SATA connector is designed for SATA backplanes.
It's usage in desktop computers is an afterthought.
The hard drive was supposed to slide into a hole
in a chassis, and the back of the drive mates
with a backplane connector that "sticks out"
of the backplane PCB board. And via hotswap, on
a server you could add or remove drives while
the server remained powered and running.

*******

The 15 pin power is 5 groups of 3 pins each.
A pin carries 1 ampere of current. Three pins
carry 3 amps. And 3 amps is just enough for the
+12V source, to run the hard drive motor. At
one time, some hard drives would draw 3 amps for
the first ten seconds, until the spindle was up
to speed.

So the contact count for power, was made generous
enough to run existing hard drives.

Actual current flow measurements, show drives
now being "all over the place" with regard to
the level of current flow at startup. I don't
think I found any samples I tested, drawing the
whole 3 amps.

The groups on the power connector are

3.3V, 5V, 12V, GND, GND

The expectation is, a design might use two of
three power sources, so only two ground groups
are needed. A conventional disk drive uses

5V, 12V, GND, GND

and so there are just enough grounds to match
the current flow level on the supply pins.

Paul