Operating system:
The low-level
software that supports a computer's basic functions, such as scheduling tasks
and controlling peripherals.
When a computer
starts, the initiating programs are loaded onto the ROM chipset. These programs
run a test to check whether all the resources and BIOS are working properly. If
there are no errors, then the OS is loaded.
Interrupt:
An interrupt is a
signal sent from a device or from software to the processor.
This will cause the
processor to temporarily stop what it is doing and service the interrupt.
Interrupts can occur during errors, when disk drives are ready to receive more data;
the user has pressed keys (control+alt+delete) to interrupt the process.
Once the interrupt
is received, the processor carries on with what it was doing or stop and
service the interrupt based on its intensity.
Buffer:
It is a temporary
memory area in which data is stored while it is being processed or transferred,
especially one used while streaming video (to ensure that the video doesn’t
keep on stopping to wait for data from the Internet) or downloading audio.
Buffers and
interrupts are often used together to allow standard computer functions to be
carried out.
Computer architecture:
Address bus: This
bus carries signals related to addresses between the processor and the memory.
It is unidirectional (travels in only 1 direction).
Data bus: This bus
sends data between the processor, the memory unit and the I/O devices. It is bi
directional (travels in 2 directions).
Control bus: This
bus carries signals relating to the control and condition of all activities
within the computer (example: read and write functions). It is unidirectional.
Registers:
These are
high-speed storage areas within a computer. All data must be represented in a
register before it can be processed.
There are several
types of registers: MAR (memory address register), MDR (memory data register),
ALU (arithmetic and logic unit), PC (program counter) and CIR (current
instruction register).
The memory unit
contains of a number of partitions. Each partition contains an Address and its
Contents. There are represented by a byte (8 bits in binary form).
Processor: This contains the ALU, which
allows arithmetic functions to be carried out.
Control Unit: This controls the operations of the memory, processor
and the I/O devices. It contains the CIR. This unit reads an instruction from
the memory and during this process; signals are generated along the control bus
telling them what to do next.
Input-Output (I/O) Devices:
These devices are the main method of entering data and getting data out of the
computer systems. Input devices convert analogue data to digital data that can
be understood by the computer, whereas output devices convert digital data to
data that can be comprehended by humans.
Fetch-Execute Cycle:
Fetch - Instruction
is fetched from the PC (program counter) and is stored in the CIR. The PC is
then increased by 1 so that the next instruction can be followed.
Execute – The
processor passes the decoded instruction as a set of control signals to the
appropriate components within the computer system. This allows each instruction
to be carried out in a logical sequence.
Addressing modes:
1.
Immediate:
The opcode is given in the operand itself
2.
Direct:
The address of the opcode is given in the operand.
3.
Indirect:
The address of the opcode is given in an address which is given by the operand.
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