The UCA 486 Adapter now supports AMD 486 & 5×86

After the initial support for Intel 486s, the Universal Chip Analyzer with the new 486 adapter now supports all 486s from AMD. I’m an avid CPU collector but I only collect Engineering sample (check my collection here!). Of course, some analysis on these ES will be published here soon, but to add support for AMD 486s, I bought some “retail” Am486 and Am5x86. Here they are:Good news : they all work well on the UCA! Here are some notes I took while testing.

Am486DX2-50 (1)Am486DX2-80NV8T (2) : 8 KB L1 Write-Through Cache. Both CPUID 0x432 with cpuid instruction not supported. Virtually undetectable from Intel DX2 : Same microcode. Same power consumption. Exact same performances. Maybe distinguishable from Intel DX2 with JTAG. Work in progress on this point.


Am486DX4-100NV8T (3) : 8 KB L1 Write-Through Cache. CPUID also 0x432 without cpuid instruction. Real nightmare to distinguish from Intel. B-Step a bit lower power (-5%) Vs AY-Step. INT Perfomance is lower than Intel DX4 (-20%). FP Performance almost identical. Power consumption is also lower (-25%). One interesting thing : In 2x mode, the CPU is exactly as fast as an Intel DX2. However, in 3x mode, it seems significantly slower than a DX4, but only in INT. Performances looks like 2.5x in INT (according to cycle count) and “real” 3x in FP. Strange. That deserves some additional investigation.

Am486DX4-120SV8B (4) – Am486DX4-100SV8B (5) : Newer core with SMI and Write-Back L1 Cache (still 8KB). CPUID instruction supported. 2x/3x Mode and WT/WB change CPUID (0x434/0x474 in 2x mode, 0x484/0x494 in 3x mode). Exact same performance than NV8T. Bit higher power consumption (+10%).

Am486DX4SV8B in 2x Write-Throught Mode
Same Am486DX4SV8B, in 3x Write-Back Mode

Am5x86-P75 (Am486DX5-133V16BGC) (6). 16KB Write-Back L1 Cache ! CPUID instruction supported. 3x/4x Mode and WT/WB change CPUID (0x484/0x494 in 3x mode mode, 0x4E4/0x4F4 in 4x mode). INT Performance identical to 486DX4-100 (looks like INT units are locked in 3x mode). FPU performance are far better (real 4x). Doesn’t support overclocking to 160 MHz.

Am5x86-P75 In 4x Write-Back Mode

Am5x86-P75 (Am486DX5-133W16BGC) (7). Same than previous one, but supports overclocking to 160 MHz with 3.6V !

Am5x86-P75 at 4×40 MHz = 160 MHz @3.6V

More 486s will soon be supported!