diff --git a/Computer_Architecture/CPU/Instruction_set_architectures.md b/Computer_Architecture/CPU/Instruction_set_architectures.md
index e51fa30..0110bf5 100644
--- a/Computer_Architecture/CPU/Instruction_set_architectures.md
+++ b/Computer_Architecture/CPU/Instruction_set_architectures.md
@@ -25,3 +25,15 @@ The name stems from Intel's internal naming conventions - every new processor th
 Over time, new instructions have been added to the x86 architecture but they all maintain backwards compatibility with preceding generations.
 
 There have been different, successive generations of x86 corresponding to their [word-size](/Electronics_and_Hardware/Binary/Signed_and_unsigned_numbers.md): 16-bit, 32-bit, 64-bit. Word size here just means how many bits the processor can work with at a time.
+
+A 34-bit processor can operate on values that are 32 bits in length. This means it has 32bit registers, a 32-bit data bus, a 32-bit address bus and so on.
+
+AMD introduced the first 64-bit processor, not Intel but they later caught up. A 64-bit x86 processor is often referred to as _x64_ or _x86-64_.
+
+### ARM
+
+Whilst x86 processors dominate the personal computer and server space, on mobile a different instruction set architecture predominates: ARM. The ARM company develops the architecture and standard which it licenses it to other companies to implment.
+
+They are preferred on mobile because they have reduced power consumption and lower costs compared to x86.
+
+With ARM processors the processor is on a single chip that contains the CPU as well as memory and other hardware.