[CSCI 50.01] LT 2

Modules 3-7

What does ALU stand for and what does it do?

Arithmetic and Logic Unit

Performs arithmetic and logic operations

Examples of Arithmetic Operations on Data

• Add

• Subtract

• Multiply

Examples of Logical Operations on Data

• Check if equal

• Bitwise-or

Register

Temporary storage location in the processor

ALU reads operands from _______.

Registers

________ are also sent to the ALU to select what operation to perform.

Control Signals

Control signals are provided by ______ and depend on the ______ executed.

Processor

Instruction currently being executed

ALU writes the result of an operation to a ______.

Register

ALU can set _____ which provide additional info about the operation’s result (e.g. overflow occurred). _____ values are also stored in _______.

Flag/s

Registers

Memory Characteristics

Location

Capacity

Unit of Transfer

Method of Accessing

Performance

Physical Type

Physical Characteristics

Organization

Location

Whether memory is internal or external

Internal Memory

Refers to devices like main memory and cache

External Memory

Peripherals like disk drives, accessible to the process via I/O controllers

Word

Natural unit of organization of memory

Size

Number of bits used to represent an integer or length of an instruction

In some systems, the _____ is the word.

Addressable Unit

Formula for length in bits of address (A) and number of addressable units (N)

Log2 (N) = A

Unit of Transfer

How much data can be read out of or written into memory at a time

Unit of Transfer for Internal Memory

Number of electrical lines into and out of memory module (64, 128 or 256 bits)

* Not necessarily equal to an addressable unit

Unit of Transfer for External Memory

Block, a significantly larger unit than a word

4 methods of accessing data

Sequential

Direct

Random

Associative

Sequential Access

• Access must be made in specific linear sequence

• Stored addressing for distinguishing records and helping in data retrieval

• Tapes (units for tape drives)

In sequential access, memory is organized into units of data called ___.

Records

How does sequential access work?

Shared read-write mechanism moved from current location to desired location, passing & rejecting intermediate records

In sequential access, ____ an arbitrary record is highly variable

Time to access

Direct Access

• Disks (disks in hard disk drive)

• Uses shared read-write mechanism

• But individual blocks/records have unique address based on physical location

How does direct access work?

• First to reach general vicinity

• Then use sequential searching, counting or waiting to reach desired location

The basic element of a semiconductor memory is the ___________ which stores a bit

Memory cell

Examples of Random Access

• Main memory

• Some caches

• SSDs

Access time of random access is ____ and is ______ of the sequence prior the accesses

Constant

Independent

Examples of Associative

Some caches

How does Associative work?

Compares desired bit locations in a word for a specified match (does this for all words simultaneously)

In associative, data is retrieved based on _______ instead of actual address

a portion of its contents

3 parameters that measure performance

Access Time

Memory Cycle Time

Transfer Rate

Access Time is also known as ___?

Latency

For access time of random-access memory, this is the time from _______ to ________.

The instant that an address is presented to memory

The instant that data is stored or made available for use

For access time of non-random-access memory, this is the time it takes to ___.

Position the read-write mechanism at the desired location

Memory cycle time

Access time + any additional time required before a second access can start

Data that is _______ needs additional _____ time to _____

Read destructively

Memory cycle time

Regenerate data

Memory cycle time primarily applies to _______ and is concerns with the _____ not the ______.

Random-access memory

System bus

Processor

Transfer Rate

Rate at which data can be read from or written to a memory unit

For random-access memory, transfer rate is equal to the ______

Reciprocal of memory cycle time

destructively

Data in DRAM is read ____________; reading from a cell will discharge the capacitor.

Transfer Rate Formula

Tn = Ta + (n/R)

Tn average read or write time in n bits

Ta average access time

R transfer rate in bits per sec (bps)

Physical Types of Memories

Semiconductor memory (EX. RAM, solid-state)

Magnetic surface memory (EX. Disks, tapes)

Optical (EX. Blu-ray)

Magneto-optical (EX. Sony MiniDiscs)

Physical characteristics of data storage

Determine what can happen to the data

Read-only Memory (ROM)

• Nonvolatile

• Semiconductor memory

• Has permanent pattern of data that can’t be changed

Read-mostly Memory

• Useful when read operations are more used than write operations

• But needs nonvolatile storage

Main memory is composed of a collection of ____________.

DRAM chips

A number of chips can be grouped together to form a ___________.

memory bank

Dynamic RAM (DRAM)

Basic building block of main memory

Prefetch Buffer

cache located on the SDRAM chip

Physical characteristics

______________ of data storage determine what can happen to the data

Volatile Memory

In ____, data decays naturally or is lost when electrical power is switched off

nonvolatile

In ________ memory, recorded data remains without deterioration until deliberately change;

No electrical power is needed to retain data

In __________ memory,  memory, data cannot be altered except by destroying the storage unit

nonerasable

Organization

Physical arrangement of bits to form words

operational code (opcode)

• Part of every instruction in machine language

• Tells the hardware what operation needs to be performed with this instruction

• A string of bits very relevant to the decode step

7 opcode categories

Data transfer

Arithmetic

Logical

Conversion

I/O

System control

Transfer of control

4 single-operand instructions

absolute, negate, increment, decrement

Bitwise operations are often referred to as “____________” that are based on Boolean operations

bit twiddling

Bitwise Operations

Most machines have operations for manipulating individual bits of a word or addressable units

cyclic shift

Rotate is also known as “_______________”.

For internal memory, capacity is typically expressed in ________.

bytes (8 bits) or words (8, 16, 32 or 64 bits)

For external memory, capacity is typically expressed in ________.

bytes

3 different physical characteristics

volatile, nonvolatile, nonerasable

Between CISC and RISC, which one has simpler functionality but longer code?

RISC

Register

is a temporary storage location within the processor

Endianness

refers to byte ordering in a multibyte scalar value

Big Endian

In __________, the most significant byte is stored in the lowest numerical address

Little Endian

In __________, the most significant byte is stored in the highest numerical address

Semiconductor memory can be ______ or ______

volatile or nonvolatile

Organization is the same as endianness. True or False?

FALSE

Semiconductor memory cells share certain properties

• 2 stable (or semistable) states to represent binary 1 and 0

• Can be written into (at least once) to set the state

• Can be read to "sense" the state

Random-access memory (RAM)

• Most common type of semiconductor memory

• Possible to read data from and write new data into RAM easily and quickly

In Random-Access Memory, Reading and writing is achieved through _____.

electrical signals

Random-Access Memory is a ______ storage.

Temporary storage

Since it is volatile and must be provided with a constant power supply

2 Traditional forms of Random-Access Memory used in computers

DRAM and SRAM

DRAM

Dynamic RAM

Dynamic RAM is made with ________ that ______

cells that store data as charge on capacitors

Presence or absence of charge in capacitor is interpreted as ___ or ___.

Binary 1 or 0

DRAM requires ______ to maintain data storage

periodic charge refreshing since capacitors naturally tend to discharge even with continuous power applied, so it’s "dynamic"

What are the following parts of the DRAM covered in yellow?

Access FET

Explicit storage capacitor

Data in DRAM is read ______.

Destructively

• Reading from a cell will discharge the capacitor

• Data must be restored as part of completing the read operation

SRAM

Static RAM

Static RAM

a digital device that uses the same logic elements in the processor

How are binary values stored in Static RAM

Using traditional flip-flop logic-gate configurations

SRAM will hold data as long as _____.

power is supplied to it

What are the parts of the Static RAM covered in yellow

static bistable storage element

word line

bit

access FET

DRAM vs SRAM

• Both are volatile

• Dynamic memory cell is simpler and smaller than a Static memory cell

DRAM and SRAM, Which is cheaper? Which provides more storage given the same physical space occupied?

DRAM is cheaper and less transistor so it occupies less space (smaller)

DRAM - main memory

SRAM - cache

True

Cheaper DRAM cell, ____ memory, ______ cost for refresh circuitry, _______ of DRAM cell

Larger memories

Fixed cost of the refresh circuitry

smaller variable cost of DRAM cell

Which one is faster, SRAM or DRAM?

SRAMs are somewhat faster than DRAMs

SRAM doesn't require a refresh cycle during a read operation

Can you write new data in Read-only memory?

normally not possible

Read-mostly Memory is not a variation on read-only memory

False

Types of ROM

Read-Only Memory (ROM)

Programmable ROM

Erasable Programmable ROM

Electrically Erasable Programmable ROM

Flash Memory

How is a ROM created?

Like any other integrated circuit chip, with the data wired into the chip during fabrication process

In Read-Only Memory, what happens if a bit is wrong?

If even one bit is wrong, the entire batch of affected ROMs must be discarded

What is the advantage of Read-Only Memory (ROM) when it's part of main memory?

no need to load data from a secondary storage device since data is already permanently stored in ROM