CPU with memory Compiled by IITG. Basic Hardware Components of a computer CPU (the brain, the thinking ) Memory ( active information) External Storage

CPU with memory

Compiled byIITG

Basic Hardware Components of a computer

• CPU (the brain, the thinking )• Memory ( active information)• External Storage (mass knowledge)• Input devices• Output devices• Communication devices

• The central processing unit (CPU) of a computer is the main unit that dictates the rest of the computer organization and performs the bulk of data processing operations.

• Central Processing Unit = “brain”

• CPU communicate with other hardware components through data buses.

Disk InputMain

Memory

ControlUnit

Registers

ArithmeticLogic Unit

Bus

I/O Devices

Output

Basic Hardware Components of a computer

• CPU (brain, the thinking )• Memory ( active information)• External Storage (mass knowledge)• Input devices• Output devices• Communication devices

Chapter 7 CPU and Memory 7-5

CPU: 3 Major Components• ALU (arithmetic logic unit)

– Performs calculations and comparisons (data changed)• CU (control unit): performs fetch/execute cycle

– Functions:• Moves data to and from CPU registers and other hardware components

(no change in data)• Accesses program instructions and issues commands to the ALU

– Subparts:• Memory management unit: supervises fetching instructions and data• I/O Interface: sometimes combined with memory management unit as

Bust Interface Unit • Registers

– Example: Program counter (PC) or instruction pointer determines next instruction for execution

Central Processing Unit

• The CPU is made up of three major parts:– Register set– ALU– Control units

• CPU must have some working space to efficiently store intermediate values (instructions or data).

• The registers are like built-in storage spaces in the processor. These space will hold the data and instructions copied from memory.

• The registers are also wired (connected) with control unit and ALU.• The registers are part of the CPU. They are located inside the CPU, instead of in RAM, so data

can be manipulated by the other two parts of the CPU.• Registers are high-speed memory.

• Registers are limited, only a dozen in a CPU.

• Registers are temporary memory. Once power is off, the data will be lost.

General Organization of Register set• There are only several registers in CPU. All the code and data get chances to be fed into

proper registers as the program runs.• Program Counter (PC) keeps tracks of the address of the instruction currently being

executed. (Where or which). • Instruction Register (IR) stores a copy of the instruction loaded from main memory.

(What), closely tied to the control unit.• General purpose registers are the one we use most of the time. most instructions perform

on these registers. Stores intermediate data during the execution of instructions; temporarily holds data taken from or about to be sent to memory. A storage register for regular operations.

• AC Accumulator stores the result of a previous computation or a value communicated with the main memory.

• Segment registers stores the positions of program segments. There are four or more segment registers: CS contains the segment of the current instruction (PC is the offset), SS contains the stack segment (SP is the offset), DS is the segment used by default for most data operations, ES is an extra segment register.

• Indexes and pointers indexes and pointer and the offset part of and address. They have various uses but each register has a specific function. They some time used with a segment register to point to far address.

• The EFLAGS register holds the state of the processor. It is modified by many instructions and is used for comparing some parameters, conditional loops and conditional jumps. Each bit holds the state of specific parameter of the last instruction.

• Special roles are assigned to certain registers. i.e. the control logic is specially wired.

• So, certain operations tend to (sometimes must) use certain registers, while most operations can use different general purpose registers freely.

instruction register• An instruction register is the part of a CPU's control unit that stores the

instruction currently being executed or decoded. In simple processors each instruction to be executed is loaded into the instruction register which holds it while it is decoded, prepared and ultimately executed, which can take several steps.

• More complicated processors use a pipeline of instruction registers where each stage of the pipeline does part of the decoding, preparation or execution and then passes it to the next stage for its step. Modern processors can even do some of the steps of out of order as decoding on several instructions is done in parallel.

• Decoding the opcode in the instruction register includes determining the instruction, determining where its operands are in memory, retrieving the operands from memory, allocating processor resources to execute the command, etc.

Why not more registers?

• The more space, the more convenient, right?• Sounds like yes, … but why not more

registers?• It more registers, means more control units,

more wires, more costly, more complicated …• Operations on registers generate heats.• The more complicated the CPU is, the more

heats generated.

The Arithmetic/Logic Unit • The abbreviation of arithmetic logic unit , ALU contains the electronic circuitry that

executes all arithmetic and logical operations to process data saved in register sets;

• As its name implies, the arithmetic/logic unit can perform both arithmetic and logic operations.– four kinds of arithmetic operations, or mathematical calculations: addition,

subtraction, multiplication, and division. – Logic operators usually are AND, OR, NOT and XOR at bits level, but at CPU

level, LU supports comparison operations two. The unit can compare two bytes to determine if one is greater than, less than, equal to, or not equal to another. The control unit can then take action based on the result of the comparison. This is a very important capability.

Control Unit• Simply put, the control unit executes programs.

• The control unit of the CPU contains circuitry that uses electrical signals to direct the entire CPU to execute instructions and transfer data.

• The functions performed by the control unit vary greatly by the internal architecture of the CPU, since the control unit really implements the architecture.

– On a regular processor that executes x86 instructions natively the control unit tyipcally performs a five step operation cycle in executing instructions: fetching, decoding, increment, managing execution of programs and then storing results.

– On a x86 processor with a RISC core or other more advanced CPUs, the control unit has significantly more work to do.

• Like an orchestra leader, the control unit does not execute program instructions; rather, it directs other parts of the system to do so.

• The control unit must communicate with both the arithmetic/logic unit and registers, as well as memory. • Control unit supervises the transfer of information among the registers and instructs the ALU as to

which operation to perform by generating control signals.

•


System Block Diagram


The Little Man Computer


Concept of Registers

• Small, permanent storage locations within the CPU used for a particular purpose

• Manipulated directly by the Control Unit• Wired for specific function• Size in bits or bytes (not MB like memory) • Can hold data, an address or an instruction• How many registers does the LMC have?


Registers• Use of Registers

– Scratchpad for currently executing program• Holds data needed quickly or frequently

– Stores information about status of CPU and currently executing program

• Address of next program instruction• Signals from external devices

• General Purpose Registers– User-visible registers– Hold intermediate results or data values, e.g., loop counters– Equivalent to LMC’s calculator– Typically several dozen in current CPUs


Special-Purpose Registers• Program Count Register (PC)

– Also called instruction pointer• Instruction Register (IR)

– Stores instruction fetched from memory• Memory Address Register (MAR)• Memory Data Register (MDR) • Status Registers

– Status of CPU and currently executing program– Flags (one bit Boolean variable) to track condition like

arithmetic carry and overflow, power failure, internal computer error


Register Operations

• Stores values from other locations (registers and memory)

• Addition and subtraction• Shift or rotate data• Test contents for conditions such as zero or

positive


Operation of Memory

• Each memory location has a unique address• Address from an instruction is copied to the MAR

which finds the location in memory• CPU determines if it is a store or retrieval• Transfer takes place between the MDR and memory• MDR is a two way register


Relationship between MAR, MDR and Memory

Address

Data


MAR-MDR Example


Visual Analogy of Memory


Individual Memory Cell


Memory Capacity

• Determined by two factors 1. Number of bits in the MAR

• LMC = 100 (00 to 99)• 2K where K = width of the register in bits

2. Size of the address portion of the instruction• 4 bits allows 16 locations• 8 bits allows 256 locations• 32 bits allows 4,294,967,296 or 4 GB

• Important for performance– Insufficient memory can cause a processor to work at 50%

below performance


RAM: Random Access Memory

• DRAM (Dynamic RAM)– Most common, cheap– Volatile: must be refreshed (recharged with power) 1000’s

of times each second

• SRAM (static RAM)– Faster than DRAM and more expensive than DRAM– Volatile– Frequently small amount used in cache memory for high-

speed access used


ROM - Read Only Memory• Non-volatile memory to hold software that is not

expected to change over the life of the system• Magnetic core memory• EEPROM

– Electrically Erasable Programmable ROM– Slower and less flexible than Flash ROM

• Flash ROM – Faster than disks but more expensive– Uses

• BIOS: initial boot instructions and diagnostics• Digital cameras


Fetch-Execute Cycle

• Two-cycle process because both instructions and data are in memory

• Fetch– Decode or find instruction, load from memory into

register and signal ALU

• Execute– Performs operation that instruction requires– Move/transform data


LMC vs. CPUFetch and Execute Cycle


Load Fetch/Execute Cycle

1. PC -> MAR Transfer the address from the PC to the MAR

2. MDR -> IR Transfer the instruction to the IR

3. IR(address) -> MAR Address portion of the instruction loaded in MAR

4. MDR -> A Actual data copied into the accumulator

5. PC + 1 -> PC Program Counter incremented


Store Fetch/Execute Cycle1. PC -> MAR Transfer the address from the

PC to the MAR



4. A -> MDR* Accumulator copies data into MDR


*Notice how Step #4 differs for LOAD and STORE


ADD Fetch/Execute Cycle

1. PC -> MAR Transfer the address from the PC to the MAR



4. A + MDR -> A Contents of MDR added to contents of accumulator



LMC Fetch/ExecuteSUBTRACT

PC MAR

MDR IR

IR[addr] MAR

A – MDR A

PC + 1 PC

IN

PC MAR

MDR IR

IOR A

PC + 1 PC

OUT

PC MAR

MDR IR

A IOR

PC + 1 PC

HALT

PC MAR

MDR IR

BRANCH

PC MAR

MDR IR

IR[addr] PC

BRANCH on Condition

PC MAR

MDR IR

If condition false: PC + 1 PC

If condition true: IR[addr] PC


Bus

• The physical connection that makes it possible to transfer data from one location in the computer system to another

• Group of electrical conductors for carrying signals from one location to another– Line: each conductor in the bus

• 4 kinds of signals1. Data (alphanumeric, numerical, instructions)2. Addresses3. Control signals4. Power (sometimes)


Bus

• Connect CPU and Memory• I/O peripherals: on same bus as CPU/memory or

separate bus• Physical packaging commonly called backplane

– Also called system bus or external bus– Example of broadcast bus– Part of printed circuit board called motherboard that holds

CPU and related components


Bus Characteristics

• Protocol– Documented agreement for communication– Specification that spells out the meaning of each

line and each signal on each line

• Throughput, i.e., data transfer rate in bits per second

• Data width in bits carried simultaneously


Point-to-point vs. Multipoint

Broadcast bus Example: Ethernet

Plug-in device

Shared among multiple devices


Motherboard• Printed circuit board that holds CPU and related

components including backplane


Typical PC Interconnections

Bus interface bridges connect different bus types


PCI Bus Connections


Instructions• Instruction

– Direction given to a computer– Causes electrical signals to be sent through specific circuits for

processing• Instruction set

– Design defines functions performed by the processor– Differentiates computer architecture by the

• Number of instructions• Complexity of operations performed by individual instructions• Data types supported• Format (layout, fixed vs. variable length)• Use of registers• Addressing (size, modes)


Instruction Elements• OPCODE: task• Source OPERAND(s)• Result OPERAND

– Location of data (register, memory)• Explicit: included in instruction• Implicit: default assumed

OPCODE SourceOPERAND

Result OPERAND

Addresses


Instruction Format• Machine-specific template that specifies

– Length of the op code – Number of operands– Length of operands

Simple 32-bit Instruction Format


Instruction Formats: CISC


Instruction Formats: RISC


Instruction Types• Data Transfer (load, store)

– Most common, greatest flexibility– Involve memory and registers– What’s a word ? 16? 32? 64 bits?

• Arithmetic– Operators + - / * ^– Integers and floating point

• Logical or Boolean – Relational operators: > < = – Boolean operators AND, OR, XOR, NOR, and NOT

• Single operand manipulation instructions– Negating, decrementing, incrementing


More Instruction Types

• Bit manipulation instructions– Flags to test for conditions

• Shift and rotate• Program control• Stack instructions• Multiple data instructions• I/O and machine control


Register Shifts and Rotates


Program Control Instructions

• Program control– Jump and branch– Subroutine call

and return


Stack Instructions• Stack instructions

– LIFO method for organizing information – Items removed in the reverse order from that in which they are

added

Push Pop


Fixed Location Subroutine Return Address Storage: Oops!


Stack Subroutine Return Address Storage


Multiple Data Instructions• Perform a single operation on multiple pieces of data

simultaneously– SIMD: Single Instruction, Multiple Data– Intel MMX: 57 multimedia instruction– Commonly used in vector and array processing applications

Documents

CPU with memory Compiled by IITG. Basic Hardware Components of a computer CPU (the brain, the thinking ) Memory ( active information) External Storage