Comp Sci - The CPU

The Central Processing Unit

Arithmetic Logic Unit

Performs calculations and logical decisions

Control Unit

Sends signals to control how data moves around the CPU.

Cache

Provides fast access to frequently used instructions and data.

Clock

The electronic unit that synchronises related components by generating pulses at a constant rate.

Bus

Collection of wires through which data and instructions are transmitted from one component to another.

Registers

Tiny, super fast pieces of onboard memory inside the CPU each with a very specific purpose.

Overall Performance of CPU:

Overall Performance of CPU:

-Clock speed:

- Measured in Hertz (Hz).

- Number of cycles per second.

- 3.2 GHz clock speed = 3.2 billion instructions can be fetched per second (theoretically)!

-Cache size:

- Temporary storage of data and instructions being read to and written from the RAM.

- Stores copies of recent data and instructions.

- Much quicker getting items from the cache than from main memory (RAM).

- Trying to avoid going and getting instructions and data from memory if we don’t need to as it costs time.

- Number of cores:

- A core is a complete copy of a CPU. - So a quad-core processor would have 4 separate processing units, each with its own: Registers, ALU, Accumulator and Control Unit

- Doubling the number of cores doesn’t simply double the overall speed.

- CPUs have to be programmed with this in mind, otherwise, this takes longer.

- Many programs are not designed to make use of multiple cores.

Fetch-Execute Cycle:

Fetch Execute Decode

Fetch

- Fetching the next instruction from main memory (RAM).

- Brings the instruction back into the CPU.

Decode

- Inspects the instruction and works out what it is that needs doing.

Execute

- Carries out the instruction.

- This could cover many things such as: Going back to main memory and grabbing some data; Performing a calculation; Storing information back into main memory.

Primary Memory

-ROM

-RAM

-Cache

-Registers

ROM

-Holds the first instructions for when the computer is first turned on

-Programs may be stored in ROM in Embedded systems

-Non volatile

-Read only

-Small in comparison to RAM

RAM

-Holds the operating system, programs and data in use by the CPU when the computer is running

-Volatile

-Read and write

-Large in comparison to ROM

Embedded System

A computer system with a dedicated function within a larger mechanical system

Typical Properties of an Embedded System:

-Low power consumption

-Low cost per unit

-Small size

-Rugged Operating ranges

Egs of Embedded Systems

-Traffic lights

-Domestic appliances

-Factory equipment

-Hospital equipment

-Engine management systems

Why is Secondary Storage needed?

ROM is read only and RAM is voaltile

Secondary Storage is needed for:

-Semi permanent storage if data that can change

-Storage of programs and data when the power is off

-Back up of data files

-Archive of data files

Optical: CD-R/RW, DVD-R/RW, Blu-Ray is suitable for…

• Suitable for read-only data distribution on a large scale.

• Suitable for small capacity situations.

Magnetic: Hard disk drive is suitable for…

• Suitable when very high data capacity is required.

• Suitable for fast access to data.

• Suitable for low-cost situations.

• Suitable for cloud storage on server farms.

Solid State: SSD, Memory sticks, Flash memory cards is suitable for…

• Suitable for low power, small embedded systems.

• Suitable for rugged applications: portable devices.

• Suitable for small to medium data capacity requirements.

• Suitable for silent operation.

• Suitable for very fast access to data.

• Suitable for situations where the devices need to be small and lightweight.

Adv + Disadv of Optical (CD-R/RW, DVD-R/RW, Blu-Ray):

• Low capacity compared to other types of storage.

• Moderate to access data.

• Thin, lightweight, and portable.

• Very cheap

Adv + Disadv of Magnetic (Hard disk drive, tape):

• High storage capacity.

• Quick to read/write speeds.

• Poor portability

• Low cost

Adv + Disadv of Solid-state (SSD, Memory sticks, Flash memory cards):

• Medium storage capacity.

• Very quick to access data.

• No moving parts, very reliable.

• No noise.

• Low power.

• Limited number of read/write cycles.

• Expensive compared to other types of storage.

• Very portable

Cloud storage:

Remote servers that store data that can be accessed over the Internet.

• Typically uses magnetic hard drives.

• Use of solid-state drives (SSDs) is increasingly popular.

Adv of Cloud Storage:

• Access your files anywhere, anytime, from any device.

• Automatic backup is possible.

• Files no longer take up any space on your own device.

• Collaborate on files easily.

Disadv of cloud storage:

• Can be costly, typically a monthly or yearly subscription cost.

• No access to files without an Internet connection.