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AMR, CNR, and ACR what are they? Christopher T Oleson October 2003 |
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In the last few years I've been seeing new slots showing up on motherboards, but I've never really known what they were or what they were for. So I decided to find out, and share my findings with all of you. There are three new slots that have shown up over the last few years. All of which take up the old ISA slot location on the motherboard. Of the three the AMR (Audio/Modem Riser) was the first to appear. Then later the CNR (Communication Networking Riser) and the ACR (Advanced Communications Riser) arrived. All three of these slots are riser slots and are not like expansion slots such as the PCI or AGP slots. A riser slot is actually an extension of the motherboard. Which allows manufactures the ability to add more to a motherboard without trying to cram more onto an already crowded board. Also, this allows manufactures the ability to add communication devices (such as modems, and LANs) to the motherboard without the interference from the motherboards noisy circuits that normally interfere with communication devices. This is actually a pretty good idea, because it allows users to add one card to the motherboard that will have audio, modem, and LAN communications all in one. Riser cards do have one drawback though; they use about twenty percent of the CPUs processing power when operating. So if you are using you're computer for CPU intensive processing (i.e. online gaming) you may decide to go with the more traditional expansion cards.
Now, where this gave the ability to design a more feature rich motherboard, the designers forgot a few things. The AMR does not support plug and play, and does not provide for expandability to other devices like LAN or Broadband. So, the AMR does have some drawbacks, but it was the first design. The next step was to make it do more, so Intel next came out with its CNR. |
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All of these supported devices give the system manufacturer many choices for designs on expansion cards. Of course there are limitations. The riser card works off of five different interfaces, of which the riser will only support four at a time. The five interfaces are AC97 (which is the interface for audio and modems), LAN connection interface or LCI (which is the interface used for Ethernet and home phone-line networking), Media Independent interface or MII (used for multi-channel audio), USB (used for new technologies such as xDSL and wireless), and System Management Bus or SMBus (used for Plug and Play). Other drawbacks are that you still lose a PCI slot (even with the shared PCI slot strategy) and the CNR is not compatible with the AMR. |
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Together all of the designs do basically the same thing. Riser cards provide the ability to add more devices to the motherboard to make a more feature rich PC. Which, isn't that what we are all really after? Although knowing that the riser cards take over the CPU's processor time, is it worth the loss? Also, there are already so many options on motherboards and so many slots; is this new method worth the hassle? The answer to these questions is really up to you, the user. As for me, I won't probably use these features on my main machine, because I use those precious CPU cycles. But when I upgrade my other machines with motherboards that have one of these features I will more than likely use a riser card for communication and audio. Reference:
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In the summer of 1998, Intel Corporation released the AMR or Audio/Modem Riser. This new riser architecture was the beginning in the PC industries struggle to lower overall system costs and increase the flexibility of the systems manufacturing process. The idea was to integrate the modem circuitry directly to the motherboard, but due to the FCC and other international telecom standards, the process was problematic. The solution was to redesign the physical structure of the modem, which was the AMR's key objective. To do this, the manufacturers took the circuitry that needed to be certified and moved it onto a separate card that attached to the main board through a riser slot. This process worked the same with audio giving the option for modem and\or audio expansion cards. Also, by moving these functions the manufacturers freed up the expansion slots for other devices.
Designed by Intel Corporation the CNR or Communications Networking Riser was released in late 2000. Similar to the AMR, the CNR uses the same technologies to implement audio and modem technologies as well as multi-channel audio, Ethernet networking, and phone-line networking. The difference between the AMR and the CNR is that the design adds the capability to reduce noise, adds plug and play capabilities, and adds the ability to expand into new technology such as xDSL. The riser also has extra pin locations that have not been assigned yet. According to my research these extra pins were left unassigned to be defined when the wireless market has become more mature. Another good point to the CNR is that it uses a shared PCI slot strategy. This strategy is that if the slot is not in use or the card in the slot is not operating, the PCI slot that it shares resources with can uses the resources.
Now, where the CNR is not backward compatible, the ACR or Advanced Communications Riser is. The ACR was developed and released in late 2000 by the ACRSIG organization (Advanced Communications Riser Special Interest Group). The ACRSIG is a collection of companies that formed to provide open standards for communication functions in PC's. Some of the organizations founders include AMD, VIA technologies, 3COM, and Lucent technologies. The ACR is like the CNR in that it supports Audio, analog modems, LAN (both Ethernet and home phone-line networking), and Broadband. It also has expandability, but unlike the CNR it has pins reserved for wireless technologies. As I said before, the ACR is backward compatible with the AMR, but the connector that the ACR uses is a PCI connector that is turned around 180 degrees (ACR will not work as a PCI slot). Also, the ACR uses similar interfaces to the CNR, but the ACR is not restricted to the number of interfaces it uses. Another good point to the ACR is that its controller is built into the south bridge not requiring a separate chip to control its activities. And lastly, in comparison to the CNR the ACR is cheaper to produce.