4.21 - Programming Language Classification

What is the typical format of machine code?

• Each instruction is split into two parts: the opcode and the operand

• The first few bits hold the opcode, the remaining bits hold the operand

• The number of bits allocated to each varies between processor designs

What is meant by opcode?

• Specifies the type of operation the CPU should perform

• e.g. ADD, LOAD, STORE, JUMP

What is meant by operand?

• The data to be operated on, or the memory address where that data is held

• A single instruction can have one or more operands

What is meant by low-level programming language?

Code that closely reflects how the CPU actually executes instructions

What is meant by high-level programming language?

Code written closer to natural language, describing what to do rather than how the CPU should do it

How is assembly language an improvement to machine code?

• Mnemonics replace binary opcodes - short, descriptive codes that are easier to remember and read

  • e.g. STO instead of 0001, ADD instead of 0010

• Symbolic addresses/labels replace binary operands, making code easier to follow

  • e.g. STO 2 instead of 0001 0010

What is an advantage of writing code in an low-level language?

• Fast and Memory efficient as it directly controls hardware

• Useful for time-critical or memory-constrained systems e.g. embedded systems, device drivers

What is an disadvantage of writing code in an low-level language?

• Difficult to write, read and debug

• Requires lots code for simple tasks

• Code written for one processor will not work on a different processor architecture

What is an advantage of writing code in an high-level language?

• Easier to write, read, debug and maintain

• The same code can run on different hardware with little or no modification

What is an disadvantage of writing code in an high-level language?

• Less control over hardware

• Generally slower than low-level

• A compiler or interpreter is needed before the CPU can execute it