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SU.HARDW.PC.CPU (2:5020/299) SU.HARDW.PC.CPU From : Anthony Koudrin 2:5030/217.27 Thu 14 Dec 95 13:17 Subj : AMD 486 FAQ WWW.AMD.COM. , . , , AMD ... Sysinfo 172.4, 172.9... , : >---------------------------------------------------------------------------- [AMD] Am486 Class CPU Devices Frequently Asked Questions --------------------------------------------------------------------------- >General Questions 1. Why do I have to turn off the internal (L1) cache for my system to run properly? This problem is usually caused by one of the following: * Running an AMD microprocessor at an incorrect speed. This can be caused by trying to run an AMD 486DX2-80 as a 486DX2-100 or 486DX4-120. * Running an AMD microprocessor at an incorrect voltage. Refer to question number 4 below. * Installing a CPU with an internal Write Back cache in an incompatible motherboard. There is information contained later in this FAQ to help determine if you have a device with an internal write back cache or not. AMD CPUs with an internal write back cache should only be used in systems which are intended to support the internal write back cache mode. 2. I am having problems with my motherboard jumper settings. Can AMD help to determine the best settings? We cannot answer motherboard specific questions, such as how to set jumpers or configure your CMOS setup. You need to contact the motherboard manufacturer or consult your motherboard manual. 386 motherboards do not support 486 CPUs. You will need to buy a new motherboard. 3. Where can I find out whose motherboards support the AMD products? There is a listing of motherboard manufacturers with AMD compatible motherboards available elsewhere on the AMD web site. See the 3-V Motherboard Manufacturers Listing page. 4. Can I run my new Am486 CPU in a 5 volt socket? The AMD 3.45 volt processors will not operate in 5 volt sockets. Most older motherboards do not support 3.45 volt processors. Check your manual. Adapters can be purchased to convert a 5 volt motherboard to 3.45 volts. Check our listing. The only adapter that has been tested at AMD is the one from Third Century. Others may work, but have not been verified. Note: It is generally better to purchase a new motherboard than to buy these adapters. One reason buying a new motherboard is better than using an adapter is that the older BIOS may not understand the requirements of the processor as far as speed is concerned. BIOS updates, from the motherboard manufacturer, are usually required with older boards. 5. What are the bus speeds for AMD CPUs? The bus speed for the Am486DX2-66 is 33MHz, the Am486DX2-80 is 40MHz, the Am486DX4-100 is 33MHz and the bus speed for the Am486DX4-120 is 40MHz. The Am486DX2 CPUs multiply the input clock by 2 and the Am486DX4 devices multiply the input clock by 3. 6. After I installed the AMD CPU I seem to have some problems. Do you have any suggestions? If you are having problems running HIMEM.SYS or DOS4GW.EXE check your motherboard CPU voltage and type settings. Running a 3.45 volt CPU at 5 volts or running a non-SL enhanced CPU as an SL enhanced part can cause these types of problems to occur. 7. My CPU seems to run fine but the BIOS reports a different type. Why? If your BIOS reports your Am486DX4-100 as a 486DX2-100 or reports your Am486DX4-120 as a 486DX4-100 you may have a BIOS error or jumpers on the motherboard may be set incorrectly. To update an old BIOS you will need to get an update from the motherboard or BIOS vendor. 8. Does AMD have warranty coverage for my CPU? If you have a damaged processor, it MUST be returned to the vendor from whom you purchased it. AMD does not warranty parts to the end user. The warranty coverage for your part is provided by the vendor from which you purchased it . 9. My system seems to run for a while and then fails. Any ideas? If the board runs properly for some period of time and then seems to fail you may have a thermal problem. The Am486DX2-80 requires a heat sink and the Am486DX4 class CPUs require a heat sink and fan. You will need to apply a thin layer of heat sink paste to assure proper heat transfer from the CPU to the heat sink. The heat sink paste can be purchased from Radio Shack or an electronics supply store. If you have intermittent problems check that the ISA bus clock is near 8MHz. The divider is in the Advanced CMOS setup. For bus speeds of 25MHz select clock/3, for 33MHz select clock/4 and for 40MHz select clock/5. Some "Green" or low power consumption motherboards may try to slow down the processor. It may be necessary to disable power management on "Green" PC motherboards to eliminate intermittent problems. The AMD standard 486 class processors are not SL Enhanced and do not support System Management Mode (SMM) power saving features. The Enhanced Am486 CPUs from AMD are SL Enhanced devices and do support SMM mode for power savings. 10. I seem to have problems with my VESA Local Bus (VL) cards. Is this a CPU problem? No. If you have problems running with a Local Bus motherboard, try running the same motherboard at 33MHz and set the Local Bus clock rate indicator jumper for <=33MHz.. If this works the problem probably lies with one or more of the Local Bus cards. Try inserting / removing wait states until the processor works properly. If the board works at 33MHz, switch the frequency to 40MHz, set the Local Bus clock rate indicator jumper for >33MHz, and try inserting / removing each of the Local Bus cards on your motherboard until the system works. Some Local Bus cards will not operate properly at 40MHz. 11. Some of my programs work with the older CPUs but fail with my new one. What could cause this to occur? Some older benchmarks and diagnostic software do not work correctly with the faster processors. If you are having problems running specific programs at 80MHz or 100MHz, you may need to contact the respective software company to determine if there is an updated version of their software available. The AMD 80486 microprocessors are fully software compatible with programs written for the x86 microprocessors. The AMD 80486DX4-100 has been GOLD CERTIFIED by XXCAL, INC. A copy of this certification can be requested through the AMD Facts on Demand or Literature Department at 800-222-9323. Request document #19758. The XXCAL report includes XXCAL certification with hardware and software compatibility information. >Standard Am486 Products 1. How can I tell if I have a 3.45 volt or 5 volt CPU? The A80486DX2-80 V8T and A80486DX2-80NV8T are 3.45 volts devices and the A80486DX2-80 and A80486DX2-80N are 5 volt parts. If you plugged a 3.45 volt part into a 5 volt board, the part may be damaged. Publication #19723A on AMD Facts on Demand explains the reason for 3.45 volts. Note: We no longer manufacture 5 volt versions. 2. My new faster CPU seems to run slower than I expected. Why is that? If your processor is running faster or slower than it should, check that pin B-13 (Bravo 13) is grounded for DX2 processors. It should be high for DX4 processors. The DX2-80 will not run reliably at 100MHz. If your computer doesn't boot, try setting the clock speed to 25MHz. If this works, pin B13 is not grounded. Use your favorite benchmark program to determine if the speed is correct. Also, check if the cache is enabled in your advanced CMOS setup. For DX4-100 the cache wait states should be 0. Your motherboard manual should indicate a special jumper setting for the Am486DX2 microprocessor. If no jumper exists, then your motherboard may not correctly support the Am486DX2 processor. If your CPU's performance is much lower than expected you may need to reduce wait states in your cache or main memory. In many cases the cache wait states may be set to zero for bus speeds of 33MHz or less. For example if you have the Am486DX4-100 you should get a benchmark result of 198 with Norton SI version 8.0. If you are getting a number of 132 or 134 instead you should try the following to see if it helps. Change the cache read cycle time from 2 to 1 and the cache write cycle time from 3 to 2. Some customers have reported that changing the cache write wait state from 1 to 0 will also correct the problem. Also, changing the DRAM speed from fast to fastest may fix the problem. If these changes don't help you will need to contact your board vendor for assistance. Note: Running the Am486DX2 CPU faster than it's rated speed will result in unreliable operation. 3. What are the benchmark numbers for the AMD 486 class CPUs? The benchmarks for the Standard Am486DX2 and Am486DX4 CPUs are listed below and there is further information on our AMD Facts on Demand service in document #19259: 486DX4-120 486DX4-100 486DX2-80 486DX2-66 --------------------------------------------------------------------------- NortonSI 237.7 198.1 172.9 144.1 Version 8.0 Winstone 113.9 102.4 97.6 87.3 '95 (Units) Power Meter 35.5 29.6 25.6 21.4 1.81 (MIPS) Landmark Speed 2329.09 1963.44 1740.47 1429.64 3.0 CPUMarks PC Bench 9.0 136.93 113.87 104.28 86.90 CPUMark16 >Enhanced Am486 Products 1. How can I tell if the device I have is an Enhanced Am486 part? The part number suffix for the AMD Enhanced 486 product line is SV8B with the S indicating that the part is "SL Enhanced", the V indicates that the part is a "3.45 volt" device and the 8B indicates that the internal cache is "8KB Write Back" capable. These devices are fully pin compatible with the Intel SL enhanced 486 device. You may be able to use this part in a motherboard that does not specifically support the AMD part by setting up your motherboard for an Intel 486DX4-100 SL Enhanced CPU. It is generally easier to use the AMD devices with a motherboard that is designed to support them. 2. What clock frequencies are available in the Enhanced Am486 products? The AMD Enhanced 486 product line includes 80MHz, 100MHz and 120MHz CPUs. These are the A80486DX2-80SV8B (40MHz x 2), A80486DX4-100SV8B (33MHz x 3) and the A80486DX4-120SV8B (40MHz x 3). 3. Can the Enhanced Am486 products be used in older motherboards designed for the standard 486 CPU? This really depends on the motherboard. The Enhanced AMD 486 CPUs have been designed so that all of the new features (SMM, Stop Clock, Write Back L1 Cache, etc) will be disabled if the socket does not support them. However, if the motherboard has done something non-standard with the 486 socket, or if the BIOS does not recognize the device properly, the motherboard may not run correctly. It is best to use a motherboard that is designed for the new devices for optimum performance. 4. My AMD Enhanced Am486DX4-120 CPU gives a Norton SI version 8.0 rating of around 118. Shouldn't it be much higher? Yes. This benchmark number should be about 259.3. The problem may be in the BIOS settings. You may want to check the following settings in the BIOS. The cache read burst cycle time should be 3-1-1-1 and the cache write wait state should be 0. You will need to disable the autoconfigure mode in your BIOS to make these changes. If this doesn't work you will need to contact your board vendor for help. 5. What are the benchmark numbers for the Enhanced AMD 486 class CPUs? The benchmarks for the Enhanced Am486DX2 and Am486DX4 CPUs are listed below and there is further information on our AMD Facts on Demand service in document #19710: 486DX4-120 486DX4-100 486DX2-80 --------------------------------------------------------------------------- NortonSI 259.4 216.1 172.9 Version 8.0 Winstone 114.5 103.4 98.5 '95 (Units) Power Meter 39.0 32.3 26.1 1.81 (MIPS) Landmark Speed 2385.63 1987.01 1763.42 3.0 CPUMarks PC Bench 9.0 136.93 113.87 104.28 CPUMark16 AMD, the AMD logo and Am486 are registered trademarks of Advanced Micro Devices, Inc. GENERAL NOTICE: Product names used in this publication are for identification purposes only and may be trademarks of their respective companies. --------------------------------------------------------------------------- Last Updated 11/21/95 1995 Advanced Micro Devices, Inc. [Navigational Tool Bar] >---------------------------------------------------------------------------- --- * Origin: Five_Angles Station (2:5030/217.27)

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