The Function of the CPU, The Von Neumann Architecture, Characteristics of the CPU, Memory, Storage

What is the CPU often known as?

The brain of the computer

What is the job of the CPU?

To process data

What are examples of data processing tasks?

Searching, sorting, calculating and decision making

What cycle does the CPU follow to process data?

Fetch - Decode - Execute cycle

Where are a program's data and instructions loaded when opened?

RAM

Where does the CPU store fetched data and instructions temporarily?

Registers

What is used by the CPU to locate the next item in memory?

Address bus

What hardware allows data to travel from RAM to the CPU?

Data bus

What happens in the decode step of the CPU cycle?

The CPU understands the instruction

What happens in the execute step of the CPU cycle?

Data processing occurs and instructions are carried out

What are the three areas of the CPU responsible for processing?

Control Unit, Cache, Arithmetic and Logic Unit (ALU)

What are the three main jobs of the Control Unit?

Managing hardware, managing input and output signals, synchronising the FDE cycle with clock signals

What were computers like before 1945?

Preprogrammed machines set up with wires and switches for specific tasks

What did a computer program used to be considered part of?

The machine

Who had a new idea about computer design in 1945?

John Von Neumann

What was Von Neumann's idea?

To store program and data together, independent of the machine

What advantage did Von Neumann’s idea offer?

The same computer could run different programs

Where are data and instructions held in Von Neumann architecture?

Together in memory

What happens to data and instructions in Von Neumann architecture?

They are fetched, decoded and executed one at a time

What did Von Neumann's design eliminate the need for?

Rewiring the circuitry to run new programs

What is an instruction set in a Von Neumann CPU?

A list of instructions the CPU understands

What does the ADD instruction do?

Add numbers together

What does the SUB instruction do?

Subtract numbers from each other

What does the STA instruction do?

Store value in the accumulator

What does the LDA instruction do?

Load value from the accumulator

What does the BRA instruction do?

Branch to a different part of the program

What does the OUT instruction do?

Output a value after processing

What happens in the first part of the fetch-decode-execute cycle?

Instructions and data are fetched from memory and loaded into specialised registers

What does the program counter do?

Keeps track of the number of steps carried out

Where is the program counter value copied to in the first step?

MAR

What does the MAR represent?

The address of the instruction to be fetched

How is the instruction found?

By looking up the value in the MAR

Where is the instruction first loaded after being fetched?

MDR

Where is the instruction moved after the MDR?

IR

How is the instruction decoded?

By looking up the IR instruction in the character set

What happens when the instruction is executed?

The value is loaded into the accumulator

What happens to the program counter after the first cycle?

It is updated to 1

What determines the speed of the fetch-decode-execute cycle?

The CPU’s clock chip

What does the CPU clock chip use to maintain a constant rate?

A vibrating crystal

What is the speed of the clock measured in?

Hertz

What does 500Hz mean?

500 cycles per second

What is a typical modern CPU clock speed?

3GHz

How many cycles per second is 3GHz?

3 billion

What is increasing a CPU’s clock speed called?

Overclocking

Why is overclocking potentially dangerous?

It makes the CPU hotter

What can’t operate at the same speed as the CPU?

RAM

How does the CPU overcome the slower speed of RAM?

By using cache memory to copy continuing instructions

Why is cache memory faster than RAM?

It has read speeds similar to the CPU

Where does the Control Unit look first for the next instruction?

Cache memory

How does a larger cache improve processing time?

It increases the chance that the next instruction is already in the CPU

What is a solution if CPUs can’t go faster?

Add more CPU chips

What are multiple CPU chips called?

Cores

What can each core do independently?

Carry out its own Fetch – Decode – Execute cycle

What does this allow a CPU to do?

Process more data during the same time period

What is parallel processing?

When two instructions of the same program are processed at the same time

What is multi-tasking with multiple cores?

Each core processes instructions from different programs at the same time

What is a computer?

A programmable machine that takes in data, processes it, and outputs the result

What is an embedded system?

A system where computers run specific tasks only

Why don’t embedded systems need separate components?

Because they won’t need updating with new software or hardware

How are the components of embedded systems arranged?

On a single circuit board

What are embedded systems typically built for?

A larger system

Why is RAM needed?

To store programs that are currently being used

What does RAM enable in computing?

Multi-tasking

How does RAM help with multi-tasking?

It copies the data needed by programs so it can be passed to the CPU when needed

How does RAM store data?

As small charges of electricity in tiny transistors

Why is RAM considered volatile memory?

Because it loses data when there is no power

Where are programs loaded from when opened by the user?

From the hard disk onto the RAM

Why are programs loaded onto RAM?

So the CPU can access data and instructions at an acceptable rate

What is a capacitor in RAM similar to?

A sink or bucket holding water

What does a full capacitor represent?

1

What does an empty capacitor represent?

0

What does the transistor in RAM do?

It acts as a switch to read or change the capacitor's state

How does Dynamic RAM store data?

In a capacitor that must be constantly refreshed

How does Static RAM store data?

Using flip-flops that do not need refreshing

What type of memory is ROM?

Non-volatile

What is ROM used for in a computer?

To store boot sequence instructions

How does flash memory store data?

By trapping electrons in position using a large electric current

What happens to unused programs to prevent system slowdown?

They are relocated to secondary storage

Why does relocating programs take time?

Because hard-disk data speeds are much slower

What is a limitation of having smaller amounts of RAM?

Limited multi-tasking and greater use of slower virtual memory

What is an advantage of having larger amounts of RAM?

Faster performance and effective multi-taskin

How does magnetic storage store data?

By using different patterns of magnetisation in a magnetisable material

What does a magnetised point represent in magnetic storage?

1

What does a demagnetised point represent in magnetic storage?

0

How does optical storage store data?

By using marks arranged in patterns, with pits and lands on the surface

What happens when a laser hits land on optical media?

The beam reflects, representing 0

What happens when a laser hits a pit on optical media?

The beam does not reflect, representing 1

How is flash memory data stored?

By forcing electrons through a barrier and trapping them in position

What does the flash of electric current in flash memory do?

It arranges electrons in a way that represents data

What is a characteristic of a hard disk?

Desktops, large (TB), high speeds, heavy, damage-prone, limited life, cheap

What is magnetic tape used for?

Backup data

What are the characteristics of magnetic tape?

Very large (TB), high write but low read, small, light, durable, reusable, cheap

What is the capacity of a CD-ROM?

Small (MB)

How durable is a CD-ROM?

Fair durability

What is the characteristic of Blue-Ray and DVD-ROM?

Written once but can be re-read unlimited times

What is the storage capacity of a Solid State Drive?

Moderate (GB)

What is the speed of a Solid State Drive?

Super fast

What are the characteristics of a Solid State Drive?

Very portable, durable, multiple re-usability, expensive

What is the storage capacity of a Flash SD card?

Small (GB)

What are the characteristics of a Flash SD card?

Super fast, extremely portable, durable, multiple re-usability, expensive