ITEC 1000 Chapter 7

Arithmetic Logic Unit (ALU)

Performs calculations and comparisons

Control unit (CU)

§ Performs fetch/execute cycle

p Accesses program instructions and issues
commands to the ALU

p Moves data to and from CPU registers and other
hardware components

Subcomponents

p Memory management unit

p I/O Interface

Memory management Unit

supervises fetching
instructions and data from memory

I/O Interface

sometimes combined with memory
management unit as Bus Interface Unit

Registers

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

§ Can hold data, an address, or
an instruction

General Purpose Registers

User-visible or program-visible registers

User-visible Register

Can be assigned to a variety of functions by the programmer

Program-visible register

used during application programming and are specified by the instructions

Program Counter Register (PC)

is a register that manages the memory address of the instruction to be executed next.

Instruction Register (IR)

is used to store the instruction word. When the CPU fetches an instruction from memory, it is temporarily stored in the __ __.

memory address register (MAR)

is the CPU register that either stores the memory address from which data will be fetched to the CPU registers, or the address to which data will be sent and stored via system bus

Memory Data Register (MDR)

is the register in a computer's CPU that stores the data being transferred to and from the immediate access storage.

Status Registers

Status of CPU and currently executing program

Status Registers

Status of CPU and currently executing program

Flags

one bit Boolean variable to track
conditions like arithmetic carry and overflow,
power failure, internal computer error

Register Operations

§ Stores values from other locations
(registers and memory)

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

DRAM (Dynamic RAM)

§ Most common, cheap, less electrical power, less
heat, smaller space

§ Volatile: must be refreshed (recharged with power)
1000’s of times each second

SRAM (static RAM)

§ Faster and more expensive than DRAM

§ Volatile

§ Small amounts are often used in cache memory for high-speed memory access

ROM

§ Read-only Memory

§ Holds software that is not expected to change over the life of the system such as firmware used
for the system BIOS

Flash Memory (SSD)

§ Inexpensive nonvolatile secondary storage

§ Useful for nonvolatile portable computer storage,
digital cameras, tablets, smartphones

§ Slower rewrite time compared to RAM

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

Bus

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

Line

each conductor in the bus

4 kinds of signals

1. Data
2.Addressing
3. Control signals
4.Power (sometimes)

Parallel Bus

§ High throughput because all bits of a word are transmitted
simultaneously

§ Expensive and require a lot of space

§ Subject to radio-generated electrical interference, which
limits their speed and length

§ Generally used for short distances such as CPU buses and
on computer motherboards

Serial Bus

§ 1 bit transmitted at a time

§ Single data line pair and a few control lines

§ For many applications, throughput is higher than for parallel because of the lack of electrical interference

Direction of transmission

§ Simplex
§ Half duplex
§ Full duplex

Simplex

unidirectional

Half duplex

Bidirectional, one direction at a time

Full duplex

Bidirectional simultaneously

Methods of interconnection

Point-to-Point
Multipoint bus

Point-to-point

single source to single
destination

Cables point-to-point

buses that connect to an
external device

Multipoint bus

also broadcast bus or multidrop
bus

Classification of Instructions

§ Data Movement (load, store)
§ Arithmetic
§ Boolean Logic
§ Single operand manipulation instructions

Data Movement

§ Most common, greatest flexibility
§ Involve memory and registers
§ What’s this size of a word ? 16? 32? 64 bits?

Arithmetic

§ Operators + - / * ^
§ Integers and floating point

Boolean Logic

Often includes at least AND, XOR, and NOT

Single operand manipulation instructions

§ Negating, decrementing, incrementing, set to 0

More Instruction Classifications

§ Bit manipulation instructions
§ Shift and rotate
§ Program control
§ Stack instructions
§ Multiple data instructions
§ I/O and machine control

Stack instructions

§ LIFO method for organizing information
§ Items removed in the reverse order from how they are
added

Push

Increments pointer, than STOREs data

Pop

Loads data, than decrements pointer

Single Instruction, Multiple Data (SIMD)

Perform a single operation on multiple pieces of data
simultaneously

Instruction

§ Direction given to a computer

§ Causes electrical or optical signals to be sent through
specific circuits for processing

Instruction set

Design defines functions performed by the processor

§ Differentiates computer architecture by the

p Number of instructions

p Complexity of operations
performed by individual
instructions

p Data types supported

p Format (layout, fixed vs. variable length)

p Use of registers

p Addressing (size, modes)

Locations of data

Explicit
Implicit

Explicit

included in instruction

Implicit

default assumed

Machine-specific

template that specifies
§ Length of the op code
§ Number of operands
§ Length of operands