Special tuned registers are used in CPUs to store information like the currently executing instruction, function call addresses, and data for arithmetic operations. There are different types including control registers for interrupt control, status registers for processor state information, floating-point registers for math, and SIMD registers for parallel operations. Special tuned registers provide faster access to frequently used data compared to general purpose registers and help optimize memory usage and program performance, but have limited capacity and increase CPU cost.

1. SPECIAL TUNED
REGISTERS
Mr.C.Ramesh KIT-CBE

2. Introduction
● A special-purpose register keeps track of the currently
executing instruction, and points to the address of this
instruction—Instruction Pointer (IP).
● This IP is stored on the stack during the function call.

3. Types of Special Tuned Registers
● Control registers
● Status registers
● Floating-point registers
● SIMD registers, etc.

4. Why Special Tuned Registers Are used?
These registers are employed for a wide range of functions, such
as holding operands and results of arithmetic and logical
operations, and providing temporary storage for data transfer
between the CPU and main memory.

5. Special Tuned Registers vs General Purpose
Registers
● Special purpose registers hold the status of a program. These
registers are designated for a special purpose. Some of these
registers are stack pointer, program counter etc.
● General purpose registers hold the temporary data while
performing different operations.

6. Control Registers
● A control register is a processor register that changes or
controls the general behavior of a CPU or other digital device.
● Common tasks performed by control registers include interrupt
control, switching the addressing mode, paging control, and
coprocessor control.

7. Status Registers
● The status register is a hardware register that contains
information about the state of the processor.
● Individual bits are implicitly or explicitly read and/or written by
the machine code instructions executing on the processor.

8. Floating point Registers
● Floating-point registers are loaded and stored from memory
using lwc1 and swc1.
● These instructions move 32 bits, so two are necessary to
handle a double-precision number.

9. SIMD Registers
SIMD (Single Instruction stream, Multiple Data stream) Within A
Register (SWAR) isn't a new idea. Given a machine with k-bit registers,
data paths, and function units, it has long been known that ordinary
register operations can function as SIMD parallel operations on n, k/n-
bit, integer field values.

10. ADVANTAGES
● It provides faster access to data, instruction, and addresses stored
in it for CPU.
● It handles the storing/retrieving variables accessed repeatedly. It
helps in enhancing program performance significantly.
● Optimized utilization of memory while executing the program

11. DISADVANTAGES
● Limited Capacity: We cannot store more data in registers as they
are designed to store only a small amount of data.
● Cost: They have higher speed because they are made with high-
speed memory cells so this will increase the cost of the CPU.