Systems architecture

Input/Output (I/O) devices

I/O devices allow users to input data into the computer, or receive a data output from the computer. Examples of common I/O devices are: Keyboard. Mouse. Monitor. Speakers.

Processors

A processor is a special component that processes data and instructions to control other components within the computer. The two main types of processor are: Central Processing Unit (CPU). Graphics Processing Unit (GPU).

Embedded systems

An embedded system is a computer system which is built into another device to support its operation. E.g. Washing machines. E.g. Digital cameras. E.g. Sat-Navs.

Cache memory

Cache memory is a small amount of very fast memory inside the CPU. In comparison to the cache, accessing the Random Access Memory (RAM) is a very slow operation. By storing frequently accessed data and instructions in cache memory we can avoid the process of accessing the RAM.

Cores

Each core of a CPU is capable of processing instructions independently. Each core has its own Control Unit (CU), and Arithmetic and Logic Unit (ALU), but the cores share access to cache and main memory. Multiple cores allows a CPU to process multiple instructions at the same time.

General purpose systems

General purpose systems are capable of performing many different tasks. E.g. PCs. E.g. Macs. E.g. Smartphones.

Memory Address Register (MAR)

Holds the address of the location in memory where data is to be retrieved or stored.

Memory Data Register (MDR)

Holds the data that has been retrieved from memory, or that is about to be stored in memory.

Program Counter (PC)

Holds the memory location address of the next instruction to be performed by the CPU.

Accumulator (ACC)

Holds the result of calculations and operations performed by the arithmetic logic unit (ALU).

Primary storage

Primary storage is the memory in which the computer can store the data or instructions that are currently in use. The two main types of primary storage are: Random Access Memory (RAM). Read-Only Memory (ROM).

Registers

Registers are tiny amounts of super-quick memory within the CPU. Used to hold information needed for the CPU to work. Each register holds a specific piece of information.

Special Purpose Registers

Registers that have a predetermined purpose within the central processing unit are known as special purpose registers.

Secondary storage

Secondary storage is the memory in which the computer can store the data or instructions which are NOT currently in use. Not all computer systems use secondary storage. The main types of secondary storage are: Hard Disk Drive (HDD). Solid State Drive (SSD). Compact Disk (CD). Flash (USB Drive).

Control Unit (CU)

Sends out control signals to other parts of the CPU. Executes program instructions by following the fetch-decode-execute cycle. Made up of two key parts: The clock - coordinates the CPU's activity. The decoder - decodes program instructions.

Arithmetic and Logic Unit (ALU)

The ALU performs all of the arithmetic and logical operations of the CPU, including: Addition and subtraction, multiplication and division. Comparisons such as whether numbers are equal or if one is greater than another. Boolean operations such as AND, OR and NOT.

Clock speed

The CPU's clock sends a pulse at fixed intervals to trigger the next stage of the fetch, decode, execute (FDE) cycle. The higher the clock speed, the more pulses are sent per second, so more instructions can be executed in the same amount of time.

Decode

The Control Unit decodes the instruction and sends control signals to the component within or outside the CPU that needs to act.

Fetch

The address of the next instruction to be processed is copied from the Program Counter (PC) to the Memory Address Register (MAR). The PC is incremented to point to the next instruction that will be needed when the cycle starts again. The instruction stored at the location held by the MAR is copied to the MDR.

Key parts of Control Units in CPUs:

The clock Coordinates the CPU's activity. The decoder Decodes program instructions.

Execute

The operation indicated by the instruction is performed by the appropriate component. For example: The Arithmetic Logic Unit (ALU) performs the operation given by the Control Unit. The value stored by the Program Counter or Memory Address Register might be changed.