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# x86-assembly-Reverse-Engineering # x86-assembly-Reverse-Engineering
Knowledge I have found interesting about the topic of x86 assembly Knowledge I have found interesting about the topic of x86 assembly
##
## x86 Registers ## x86 Registers
*(Older Text from the University of Virginia Computer Science (2006), one of the best Guides for x86 Assembly)*
Modern (i.e 3**86** and beyond) x**86** processors have eight 32-bit general purpose registers, as depicted in Figure 1. **The register names are mostly historical**. For example, **EAX** used to be called the accumulator since it was used by a number of arithmetic operations, and **ECX** was known as the counter since it was used to hold a loop index. Whereas most of the registers have lost their special purposes in the modern instruction set, by convention, two are reserved for special purposes — **the stack pointer (ESP)** and the **base pointer (EBP).**
For the **EAX**, **EBX**, **ECX**, and **EDX** registers, subsections may be used. For example, the least significant 2 bytes of **EAX** can be treated as a 16-bit register called **AX**. The least significant byte of **AX** can be used as a single 8-bit register called **AL**, while the most significant byte of **AX** can be used as a single 8-bit register called **AH**. These names refer to the same physical register. When a two-byte quantity is placed into **DX**, the update affects the value of **DH**, **DL**, and **EDX**. These sub-registers are mainly hold-overs from older, 16-bit versions of the instruction set. However, they are sometimes convenient when dealing with data that are smaller than **32-bits (e.g. 1-byte ASCII characters)**.
When referring to registers in assembly language, **the names are not case-sensitive**. For example, the names **EAX** and **eax** refer to the **same register**.
![x86 assembly Registers](x86-registers.png) ![x86 assembly Registers](x86-registers.png)
In **x86 registers** have an '**e**' in front of their name.</br>
Example: **e**ax, **e**bx, **e**cx, **e**dx, **e**bp
*Additional Info: </br>
In **x64** you have a '**r**' instead.</br>
Example: **r**ax, **r**bx, **r**cx, **r**dx, **r**bp</br>
You also have **double-precision floating point going from xmm0 to xmm15**.*