![[H]ard|Forum](/styles/hardforum/xenforo/logo_dark.png){kind=logo}
- Joined
- Dec 19, 2005
- Messages
- 18,559
“These lookup tables are used for the ALU configuration – as in the above schematic – making for a very flexible but also complex system, where the same microcode can be used by multiple instructions. This is effectively the very definition of a CISC-style processor, a legacy that the x86 ISA would carry with it even if the x86 CPUs today are internally more RISC-like. Decoding a single instruction and having it cascade into any of a variety of microcodes and control signals is very powerful, but comes with many trade-offs.
Of course, as semiconductor technology improved, along with design technologies, many of these trade-offs and disadvantages became less relevant. [Ken] also raises the interesting point that much of this ALU control technology is similar to that used in modern-day FPGAs, with their own reconfigurable logic using LUTs that allow for on-the-fly reconfiguration.”
Source: https://hackaday.com/2026/01/29/the-inner-workings-of-the-intel-8086s-arithmetic-logic-unit/
Of course, as semiconductor technology improved, along with design technologies, many of these trade-offs and disadvantages became less relevant. [Ken] also raises the interesting point that much of this ALU control technology is similar to that used in modern-day FPGAs, with their own reconfigurable logic using LUTs that allow for on-the-fly reconfiguration.”
Source: https://hackaday.com/2026/01/29/the-inner-workings-of-the-intel-8086s-arithmetic-logic-unit/
