I think you mean AHCI.
If he uses an add-in card (ExpressCard etc), the chip in there
will have its own driver and the driver can be AHCI without
affecting the rest of the laptop. (AHCI supports hotplug, so the
drive can be disconnected or connected hot, gets detected and so on.)
Many laptops shipping today, are set to AHCI mode for the Southbridge
as the default. My laptop is that way, and it's a low end model.
*******
There is little difference between SATA and ESATA electrically.
ESATA has a slightly different electrical spec, which helps it
support a longer cable. The Southbridge on some chipsets, supports
both standards on the same port (and doesn't even appear to have
a config bit to distinguish between them that I could see). So in
some cases, it would appear they're one in the same port. The port
just uses ESATA voltage levels at all times, even when talking
to internal disks.
Because ESATA is an external connector, they use a different connector
for it. The ESATA connector is unique, in that it is made of metal
and can withstand 5000 plug/unplug cycles. If someone substitutes
a desktop style SATA plug, those are only rated for around 50 cycles.
Early in the life of ESATA, some products shipped with SATA faceplate
plugs instead of the proper ESATA ones. The proper ESATA ones will
give a much longer life.
An external drive needs a source of power. If your external drive
has its own power adapter, then you have nothing to worry about.
2.5" drives run from 5V. A source of power could be a wall adapter,
but the necessary power could also be "bus power". In the case of a
USB external 2.5" drive, the bus power comes from the VCC and GND
pins of the USB cable.
3.5" drives run from 5V and 12V. You're more likely to find packaged
with your drive enclosure, an adapter for the purpose.
To further complicate matters, they also make a combination external port,
which apparently still isn't covered by standards. The intention is to
provide a source of power, such that there is less of a need for an adapter.
http://www.hitechreview.com/uploads/2009/05/msi-power-esata-11.jpg
That increases the number of cable types you might find, and also the
number of external drive packages you might find.
This page shows the pinout of the connectors.
http://www.addonics.com/technologies/euhp.php
On a laptop, there is a good chance, that no matter whether the ESATAP
is on the body of the laptop, or is added via an ExpressCard, there won'tbe
a source of +12V (the pins on the "ears" are missing). In such a case, if
you want to run a 3.5" ESATA drive with a laptop, nothing has really changed
with respect to the situation. Before ESATAP, your external 3.5" drive
provided its own power, and in this laptop case, it would still be providing
its own power.
If you had ESATAP on a laptop, that would offer +5V to run a 2.5" drive, in
the same way that a USB enclosure for a 2.5" drive relies on bus power.
Vanilla ESATA has no power on it.
ESATAP can have 5V or 12V, where in a laptop case, it would appear "too hard"
for them to offer 12V. If you have a desktop computer, and it had ESATAP,
that's more likely to have 12V and run 3.5" drives without an adapter.
If you use 2.5" ESATA drives, with ESATAP connectors, then that's more likely
to work with everything.
All of this stuff isn't a big deal, just something to keep in mind when
shopping for cards and enclosed disks.
*******
USB3 is also a viable alternative for external drives. USB3 uses a different
connector than USB2, since the USB3 section uses the same flavor of high speed
interconnect as is used on SATA and PCI Express (low amplitude differential).
USB3 includes 5V bus power, making it a natural for 2.5" drives.
There are undoubtedly connector options for USB3 as well (I'm sure someone
has managed to deviate the spec by now
)
USB3 enclosure chips have managed up to 200MB/sec transfer rates, which
is more than enough to cover the sustained rate of any conventional
rotating hard drive. My best drive here is around 125MB/sec sustained,
and there are a few drives that do around 135MB/sec. Those numbers are
too high for USB2, but no problem for USB3. And SATA I handles the 125MB/sec
pretty well, with the SATA II being needed if you wanted to see the 135MB/sec
delivered or not.
*******
I'm not sure that ESATA handles more than SATA II rates. (My search engines
aren't helping me here.)
Paul
