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    <p>The <code>cpuid</code> instruction, used with <code>EAX=0</code> will return a 12-character vendor string in <code>EBX</code>, <code>EDX</code>, <code>ECX</code>, in that order.</p> <p>For Intel, this string is "GenuineIntel". For AMD, it's "AuthenticAMD". Other companies that have created x86 chips have their own strings.The <a href="http://en.wikipedia.org/wiki/CPUID" rel="noreferrer">Wikipedia page</a> for <code>cpuid</code> has many (all?) of the strings listed, as well as an example ASM listing for retrieving the details.</p> <p>You really only need to check if ECX matches the last four characters. You can't use the first four, because some Transmeta CPUs also start with "Genuine"</p> <ul> <li>For Intel, this is <code>0x6c65746e</code></li> <li>For AMD, this is <code>0x444d4163</code></li> </ul> <p>If you convert each byte in those to a character, they'll appear to be backwards. This is just a result of the little endian design of x86. If you copied the register to memory and looked at it as a string, it would work just fine.</p> <p>Example Code:</p> <pre><code>bool IsIntel() // returns true on an Intel processor, false on anything else { int id_str; // The first four characters of the vendor ID string __asm__ ("cpuid":\ // run the cpuid instruction with... "=c" (id_str) : // id_str set to the value of EBX after cpuid runs... "a" (0) : // and EAX set to 0 to run the proper cpuid function. "eax", "ebx", "edx"); // cpuid clobbers EAX, ECX, and EDX, in addition to EBX. if(id_str==0x6c65746e) // letn. little endian clobbering of GenuineI[ntel] return true; else return false; } </code></pre> <p>EDIT: One other thing - this can easily be changed into an <code>IsAMD</code> function, <code>IsVIA</code> function, <code>IsTransmeta</code> function, etc. just by changing the magic number in the <code>if</code>.</p>
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    1. POHow to detect what CPU is being used during runtime?
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    1. COYou could even make a function `int Last4()` that returns the last four characters as an int using the inline assembly, and then make `bool IsIntel() { return Last4() == 0x6c65746e; }` and `bool IsAMD() { return Last4() == 0x444d4163; }` quite easily. It also avoids code duplication and reduces the overall amount of inline assembly required.
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