Use of Hydroponics Review

The CPU

Systems

A system is a collection of parts that work together for a common purpose

Input      >          Process          >    Output

Embedded systems are systems inside a larger system, for example washing machines and dishwashers. It is software that is programmed to carry out a number of dedicated functions.

Von Neumann architecture

American mathematician John Von Neumann invented a new style of computer which enabled instructions and data to be separated from the machine. In particular he invented the architecture of the CPU which allowed this to happen.[pic 1]

The CPU’s purpose is to process instructions, it takes carries out instructions on the data it is given. It follows three steps in order to process data: which is known as the Fetch - Decode - Execute cycle.

The three main parts of the CPU responsible for the cycle are the:

•        Control Unit

•        Immediate Access Store (IAS)

•        Arithmetic and Logic Unit (ALU)

The fetch-decode-execute cycle starts with both the data and the program that executes the data being loaded into main memory (RAM) by the operating system. The CPU fetches the instruction from the main memory (the hard drive) and stores it in the CPU temporary memory. Once the instruction has been fetched, the CPU will need to understand the instruction to action it. This is where the CPU decodes the instruction. When the instruction has been decoded, the CPU can execute the action needed. The Control unit runs the fetch-decode-execute cycle.

Cache

Cache is simply a few megabytes of memory that sits inside the CPU.

Being located in the CPU means that the data access speed is equal to the CPU’s speed.

Well written programs will make sure that sets of regularly used instructions are copied to the cache so that the program can run more efficiently and much faster.

ROM & RAM

[pic 2]

RAM gets used up on a device by programs being run that require RAM. You can use a hard drive however they are very slow to process the memory.

Secondary storage is needed so that there is a place to store data that needs to be retained when power is turned off. This is non-volatile memory.

RAM cannot be used to permanently save files because it has a small capacity and it loses everything stored in it when the power is turned off; it is volatile.

Types of secondary storage:

Optical

On these disks binary data is stored as variations of height on the surface in the, in the form of patterns or dots (binary 0s and 1s). When light is shined from an optical drive the light that hits a pit reflects differently to a land allowing the drive to detect the differences and read the data. The data is written with a laser burning the pits into the medium. Examples: CDs, DVDs

Properties:                                                                                                                                                                                                                                                                                                                                                ◊ Per unit, they have a small capacity(less than a 1GB)                                                                   ◊ Fairly reliable and durable, easy damaged                                                                                ◊ Good portability- easy to transport and carry

Magnetic

Magnetic storage devices use read and write heads that contain electromagnets. A small part of the storage surface is either magnetised or demagnetised and the heads control this and read what state they are in. Examples: magnetic tape, hard disks

Properties:                                                                                                                              ◊ Large capacity and cheap to buy                                                                                  ◊ usually reliable, but not that durable                                                                                          ◊ generally not very portable                                

Solid-state

This is a form of flash memory that is non-volatile unlike magnetic and optical; meaning that there are no moving parts. They consist of circuits with complex logic gates that retain data which can then be changed.                                    Examples: SD card, memory stick

Properties:                                                                                                                             ◊ Very fast for storage but very expensive                                                                                      ◊ Very reliable as they are non-mechanical, also more durable                                                ◊ Smaller capacity than magnetic                                                                                                  ◊ USB drives in particular are portable            

Algorithms

An algorithm is simply a set of steps/instructions needed to complete a task.

When the word algorithm is used in computing it defines the way in which a software task can be completed or the way a problem can be solved; writing algorithms is all about problem solving.

Abstraction

Abstraction is where you cut out all the unnecessary information to make the problem much simpler and easier to solve