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Computer organisation and
architecture
Last edited time @October 1, 2023 10:41 AM
Status Done
Internal hardware of a computer
Processor → A device that carries out computation on data by following instructions, in
order to produce an output. It processes everything insight a computer and acts as the
‘brain’. The more cores it has the more instructions it can process simultaneously. The
higher clock speed the more instructions it can process every second. It is made up of
transistors which control the flow of electrical pulses.
The processor can address memory, the range of addresses it can reach is called the
word length. i.e. A word length of 8-bits, means it can address 256 different memory
locations.
Main memory
Random Access memory (RAM) → temporary storage that can be accessed very
quickly. Ram is made up of a series of silicon chips that have individual cells. Each
cell can store an instruction or piece of data. In total there are millions of cells. RAM
stores the applications and data that are currently in use by the user but not being
processed by the processor.
Each cell can be accessed individually by the processor by referencing it
address. The length of this address is called the memory word length.
RAM is volatile → It loses all data contained within it when the computer is
powered down.
Read Only memory (ROM) → ROM is non-volatile. It is read-only meaning you
cannot put data onto ROM whilst the computer is running. It typically stores the
settings for the BIOS and the setup of the computer.
Buses
Bus → Microscopic parallel wires that transmit data between internal components.
Data bus
Computer organisation and architecture 1
, Data bus → Bi-directional bus that carries the data both to and from memory and to
and from I/O controllers. The data bus also carries data from memory to and from
the processor.
An 8-bit data bus has 8 parallel wires. These can either be 1 or 0 meaning that we
can transmit any item of data less than 8-bits long. This means that large data has to
be split up so that it can be transmitted down the bus. The data bus affects the
performance of the computer greatly.
The width of the data bus (number of parallel wires) is often the same as the
processor and memory word length.
Address bus
Address bus → Used to specify a physical address in memory so that the data bus
can access it. It is uni-directional flowing from the processor to memory. It is used to
access any address in memory not just instructions.
The size of the address bus also represent the number of directly addressable
memory locations. This means that an 8-bit bus could only handle 256 different
memory locations.
Control bus
Control bus → A bi-directional bus which sends control signals to the registers, data
and address buses. It synchronises the different parts of the computer by
transmitting the clock’s pulse. This means it controls the flow of data around the
computer.
Input/Output (I/O) controllers
An Input/Output controller buffers data sent to the processor from the devices so that
it is not left waiting for data. It also translate signals from the device into a form that
the processor can understand. These allow devices to be connected to the
processor at any time.
Before controllers, there I/O ports that allow devices to be connected to the
computer. These have buses which transport data to the processor.
Von Neumann and Harvard architectures.
Von Neumann architecture → a technique for building a processor where data and
instructions are stored in the same memory and addressed via buses.
Harvard architecture → A technique for building a processor that uses separate
buses and memory for data and instructions. It runs more quickly than the Von
Neumann architecture as the data and address buses are separated between the
data and instructions. It is widely used in embedded systems, mobile phones and
general purpose systems.
Computer organisation and architecture 2
Computer organisation and
architecture
Last edited time @October 1, 2023 10:41 AM
Status Done
Internal hardware of a computer
Processor → A device that carries out computation on data by following instructions, in
order to produce an output. It processes everything insight a computer and acts as the
‘brain’. The more cores it has the more instructions it can process simultaneously. The
higher clock speed the more instructions it can process every second. It is made up of
transistors which control the flow of electrical pulses.
The processor can address memory, the range of addresses it can reach is called the
word length. i.e. A word length of 8-bits, means it can address 256 different memory
locations.
Main memory
Random Access memory (RAM) → temporary storage that can be accessed very
quickly. Ram is made up of a series of silicon chips that have individual cells. Each
cell can store an instruction or piece of data. In total there are millions of cells. RAM
stores the applications and data that are currently in use by the user but not being
processed by the processor.
Each cell can be accessed individually by the processor by referencing it
address. The length of this address is called the memory word length.
RAM is volatile → It loses all data contained within it when the computer is
powered down.
Read Only memory (ROM) → ROM is non-volatile. It is read-only meaning you
cannot put data onto ROM whilst the computer is running. It typically stores the
settings for the BIOS and the setup of the computer.
Buses
Bus → Microscopic parallel wires that transmit data between internal components.
Data bus
Computer organisation and architecture 1
, Data bus → Bi-directional bus that carries the data both to and from memory and to
and from I/O controllers. The data bus also carries data from memory to and from
the processor.
An 8-bit data bus has 8 parallel wires. These can either be 1 or 0 meaning that we
can transmit any item of data less than 8-bits long. This means that large data has to
be split up so that it can be transmitted down the bus. The data bus affects the
performance of the computer greatly.
The width of the data bus (number of parallel wires) is often the same as the
processor and memory word length.
Address bus
Address bus → Used to specify a physical address in memory so that the data bus
can access it. It is uni-directional flowing from the processor to memory. It is used to
access any address in memory not just instructions.
The size of the address bus also represent the number of directly addressable
memory locations. This means that an 8-bit bus could only handle 256 different
memory locations.
Control bus
Control bus → A bi-directional bus which sends control signals to the registers, data
and address buses. It synchronises the different parts of the computer by
transmitting the clock’s pulse. This means it controls the flow of data around the
computer.
Input/Output (I/O) controllers
An Input/Output controller buffers data sent to the processor from the devices so that
it is not left waiting for data. It also translate signals from the device into a form that
the processor can understand. These allow devices to be connected to the
processor at any time.
Before controllers, there I/O ports that allow devices to be connected to the
computer. These have buses which transport data to the processor.
Von Neumann and Harvard architectures.
Von Neumann architecture → a technique for building a processor where data and
instructions are stored in the same memory and addressed via buses.
Harvard architecture → A technique for building a processor that uses separate
buses and memory for data and instructions. It runs more quickly than the Von
Neumann architecture as the data and address buses are separated between the
data and instructions. It is widely used in embedded systems, mobile phones and
general purpose systems.
Computer organisation and architecture 2
