The mode bits are represented here. They determine the mode in which the processor operates, and the registers that are accessible.

USR (User) PC, R14 to R0, CPSR

FIQ PC, R14_fiq to R8_fiq
R7 to R0, CPSR, SPSR_fiq

IRQ PC, R14_irq, R13_irq
R12 to R0, CPSR, SPSR_irq

SVC (Supervisor) PC, R14_svc, R13_svc
R12 to R0, CPSR, SPSR_svc

ABT (Abort) PC, R14_abt, R13_abt,
R12 to R0, CPSR, SPSR_abt

UND (Undefined) PC, R14_und, R13_und
R12 to R0, CPSR, SPSR_und

SYS (System) PC, R14 to R0
CPSR (ARM architecture v4 and above)