lOMoAR cPSD| 5967629
FIT1047-Exam Revision
Introduction to Computers, Networks and Security (Monash University)
FIT1047 – Exam Revision Notes
Computer Architecture
The Von Neumann architecture consists of a Central Processing Unit (CPU), the memory, and
the input/output devices. Furthermore, the CPU can be subdivided into the Arithmetic/Logic
Unit (ALU), a number of registers, and the Control Unit (CU).
Central Processing Unit (CPU)
A Central Processing Unit, or CPU, is the component of a computer that does most of the actual
“computing”. Almost all modern computers are based on the same architecture, called the Von
Neumann architecture, where the instructions that make up the programs we want to run, as well as
the data for those programs, are stored in the memory, and the CPU is connected to the memory by
a set of wires called the bus. The bus also connects the CPU to external devices (such as the screen, a
network interface, a printer, or input devices like touch screens or keyboards).
Compilers
A compiler takes a program in a language like Java or C++ and translates it into a lower level
language.
Interpreters
An interpreter executes, or interprets, the instructions written in an interpreted programming
language such as Python, without first translating them into machine code. The interpreter is itself a
program, usually written in a compiled programming language (so it can run directly on the CPU).
Machine Code
Machine code is a very low-level programming language. A program in machine code is a sequence
of individual instructions, each of which is just a sequence of bits. Usually, an instruction consists of
one or more words.
, lOMoAR cPSD| 5967629
Registers
A register is a very fast memory location inside the CPU. Each register can typically only store a single
word, but it is many orders of magnitude faster to read from or change the value in a register
compared to accessing the main memory.
Arithmetic Logic Unit
The arithmetic logic unit (ALU) is responsible for performing basic computations such as addition and
multiplication, as well as Boolean logic operations, for example comparisons or AND and OR
operations.
Control Unit
The control unit (CU) performs the fetch, decode and execute cycle / is the actual “machine” inside
the CPU. It coordinates the other components. For example, it can switch the memory into “read” or
“write” mode.
Fetch
The PC register contains the memory address where the next instruction to be executed is stored. In
the fetch cycle, the CU transfers the instruction from memory into the IR (instruction register). It then
increments the PC by one, so that it points to the next instruction again. This concludes the fetch
cycle.
Decode
In the decode cycle, the CU looks at the instruction in the IR and decodes what it “means”. For
example, it will get any data ready that is required for executing the instruction.
Execute
In the execute cycle, the actual operation encoded by the instruction needs to be performed. For
example, the CU may load a word of data from memory into a register, switch the ALU into “addition
mode”, and store the result of the addition back into a register.
When the execute cycle concludes, the control unit starts again with the next fetch.
MARIE CODING
AC (accumulator): This is the only general-purpose register.
MAR (Memory Address Register): Holds a memory address of a word that needs to be read from or
written to memory.
MBR (Memory Buffer Register): Holds the data read from or written to memory.
IR (Instruction Register): Contains the instruction that is currently being executed.
PC (Program Counter): Contains the address of the next instruction.
OPCODE MNEMONIC EXPLANATION
0001 Load X Load value from location X into AC
0010 Store X Store value from AC into location X
, lOMoAR cPSD| 5967629
OPCODE MNEMONIC EXPLANATION
0011 Add X Add value stored at location X to current value in AC
0100 Subt X Subtract value stored at location X from current value in AC
0101 Input Read user input into AC
0110 Output Output current value of AC
0111 Halt Stop execution
1010 Clear Set AC to 0
1000 SkipCond X Skip next instruction under certain condition (depends on X)
1001 Jump X Continue execution at location X
1011 AddI X Add value pointed to by X to AC
1100 JumpI X Continue execution at location pointed to by X
1101 LoadI X Load from address pointed to by X into AC
1110 StoreI X Store AC into address pointed to by X
Sequential Circuits
Feedback
The main mechanism that allows a circuit to remember the past is to pass its output back into its
input. That way, we can establish a feedback loop.
FIT1047-Exam Revision
Introduction to Computers, Networks and Security (Monash University)
FIT1047 – Exam Revision Notes
Computer Architecture
The Von Neumann architecture consists of a Central Processing Unit (CPU), the memory, and
the input/output devices. Furthermore, the CPU can be subdivided into the Arithmetic/Logic
Unit (ALU), a number of registers, and the Control Unit (CU).
Central Processing Unit (CPU)
A Central Processing Unit, or CPU, is the component of a computer that does most of the actual
“computing”. Almost all modern computers are based on the same architecture, called the Von
Neumann architecture, where the instructions that make up the programs we want to run, as well as
the data for those programs, are stored in the memory, and the CPU is connected to the memory by
a set of wires called the bus. The bus also connects the CPU to external devices (such as the screen, a
network interface, a printer, or input devices like touch screens or keyboards).
Compilers
A compiler takes a program in a language like Java or C++ and translates it into a lower level
language.
Interpreters
An interpreter executes, or interprets, the instructions written in an interpreted programming
language such as Python, without first translating them into machine code. The interpreter is itself a
program, usually written in a compiled programming language (so it can run directly on the CPU).
Machine Code
Machine code is a very low-level programming language. A program in machine code is a sequence
of individual instructions, each of which is just a sequence of bits. Usually, an instruction consists of
one or more words.
, lOMoAR cPSD| 5967629
Registers
A register is a very fast memory location inside the CPU. Each register can typically only store a single
word, but it is many orders of magnitude faster to read from or change the value in a register
compared to accessing the main memory.
Arithmetic Logic Unit
The arithmetic logic unit (ALU) is responsible for performing basic computations such as addition and
multiplication, as well as Boolean logic operations, for example comparisons or AND and OR
operations.
Control Unit
The control unit (CU) performs the fetch, decode and execute cycle / is the actual “machine” inside
the CPU. It coordinates the other components. For example, it can switch the memory into “read” or
“write” mode.
Fetch
The PC register contains the memory address where the next instruction to be executed is stored. In
the fetch cycle, the CU transfers the instruction from memory into the IR (instruction register). It then
increments the PC by one, so that it points to the next instruction again. This concludes the fetch
cycle.
Decode
In the decode cycle, the CU looks at the instruction in the IR and decodes what it “means”. For
example, it will get any data ready that is required for executing the instruction.
Execute
In the execute cycle, the actual operation encoded by the instruction needs to be performed. For
example, the CU may load a word of data from memory into a register, switch the ALU into “addition
mode”, and store the result of the addition back into a register.
When the execute cycle concludes, the control unit starts again with the next fetch.
MARIE CODING
AC (accumulator): This is the only general-purpose register.
MAR (Memory Address Register): Holds a memory address of a word that needs to be read from or
written to memory.
MBR (Memory Buffer Register): Holds the data read from or written to memory.
IR (Instruction Register): Contains the instruction that is currently being executed.
PC (Program Counter): Contains the address of the next instruction.
OPCODE MNEMONIC EXPLANATION
0001 Load X Load value from location X into AC
0010 Store X Store value from AC into location X
, lOMoAR cPSD| 5967629
OPCODE MNEMONIC EXPLANATION
0011 Add X Add value stored at location X to current value in AC
0100 Subt X Subtract value stored at location X from current value in AC
0101 Input Read user input into AC
0110 Output Output current value of AC
0111 Halt Stop execution
1010 Clear Set AC to 0
1000 SkipCond X Skip next instruction under certain condition (depends on X)
1001 Jump X Continue execution at location X
1011 AddI X Add value pointed to by X to AC
1100 JumpI X Continue execution at location pointed to by X
1101 LoadI X Load from address pointed to by X into AC
1110 StoreI X Store AC into address pointed to by X
Sequential Circuits
Feedback
The main mechanism that allows a circuit to remember the past is to pass its output back into its
input. That way, we can establish a feedback loop.
