The ISA bus has been around
for a very long time.  Ever since the introduction of the 8088
processor, the personal computer came with an 8bit ISA slot, which is
the front half of today’s 16bit ISA slot.  A 16bit ISA slot
running at 7Mhz doesn’t provide for a lot of bandwidth.  Today’s
computers only feature two, or sometimes only one ISA slot to support
legacy devices.  The legacy devices they are referring to are
mostly Sound Cards and Modems.

With today’s Winmodem
technology, which provides a cheap physical modem that uses the
processing power of the CPU, the ISA slot and interface circuitry is
a waste of money.  Intel, along with others, have made a new slot
standard that is intended to phase out the ISA bus, in order for
cheaper, and smaller modems to be used.

The Audio/Modem Riser Slot, or
AMR for short, is basically just an interface between the motherboard
and the phone line.  The card that is intended to plug into the
AMR has no onboard processing power at all.  For all functions,
it uses the CPU’s processing power.  Although this provides for
cheap and easy-to-make modems, this cuts about 20% of the CPU power
off from the user.

Without a hardwired
controlling chip, the card relies on special software drivers, to make
it work.  This is contrary to how a normal modem works.  A
normal modem, also called a "Hardware Modem", has an onboard
processor that does all the work and rarely needs to bother the
CPU.  An AMR modem also provides for an easy upgrades. 
Let’s say that someone buys a 56K V.90 modem for an AMR slot. 
They install it and surf with it regularly.  Then, about 3
months later, a new standard comes out, magically providing 128Kbps
over standard phone lines.  The user would then simply have to go
to the Modem Manufacturer’s website, and download, possibly with a
purchase price, a special driver made to use the modem at the new
standard.  No Firmware flashing and no chip replacing. 
They are using the same card and the same phone line, just different
drivers.

An AMR very cheap, but you get
what you pay for.  An AMR modem is only recommended for someone
that doesn’t want to play online games, because, while playing the
game online, about 20% of the Processing power, used to kick out the
Frame Rates, will be sucked up by the modem.  If you’re a gamer,
you’ll want to stay with a hardware modem.  An AMR modem is fine
for that person looking for the cheap PC to get on the Internet and
use e-mail, being it’s so cheap and easy to upgrade.