How Many Registers In X86
I believe the discrepancy between 40 and actual sum of 48 is more often than not an fault, however at that place are many other registers used for handling hardware, retentiveness direction, and command of unlike features of the CPU.
The reply yous linked to covers all the commonly used registers in the post-obit image (taken from there):
There are, even so plenty of less commonly known registers. Those registers are non probable used by user way programs but used to command and initialize the processor and low-level constructs the CPU is enlightened of. They control CPU subsystems such as the MMU unit, task scheduling, etc. Documentation of those registers can be establish in the AMD64 Architecture Manual.
You can see most of them in the following effigy, taken from the AMD64 Architecture Manual:
Non in the above picture is the new Extended Control Registers family unit of registers, for which only XCR0 is currently defined.
The Organization Registers are role of the Model Specific Registers that, as the name implied, are model specific. The variety also changes between CPUs. A full list for the AMD64 compages can be found in "Appendix A MSR Cross-Reference" of the AMD64 Architecture Manual.
There are extensions that certain AMD64 based CPUs support/implement that extend the set of XMM registers available. The XMM (and later on YMM and ZMM) are currently extended to up to 32 registers of 512 bit each in AVX-512. Like to general registers, XMM registers permit access to the lower parts of their YMM and ZMM counterparts.
There are additionally what's called "memory mapped registers" which basically ways those registers are accessed through retentiveness operations instead of designated instructions. They can be, depending on your definition, countered as registers. Ane such instance is the "APIC Registers" described in section 16.iii.2 of the AMD64
There are even internal registers that are not exposed through the instruction gear up but are used for performance reasons.
How Many Registers In X86,
Source: https://reverseengineering.stackexchange.com/questions/19693/how-many-registers-does-an-x86-64-cpu-actually-have
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