What is a program counter?(PC) (its a type of register btw)
Contains a binary number representing a location in memory where the next instruction is to be fetched from. Once instruction fetched, program counter is incremented
What is an accumulator?
Stores the result of the latest operation from the ALU. Its output can also be used as an input to the ALU.
Rmb its a type of register
What is an instruction register?
contains a binary number to tell the ALU what operations to perform.
Did you know its a type of register
What is the ALU?
A set of gates and flip flops, arranged as full - adders, shift registers and bit-testers.
Precise signal path through ALU is determined by the state of a set of control inputs which are set by the contents of the instruction register.
What defines a computer? And how is it different from a calculator?
A machine that can perform a sequence of arithmethic and logical operations by following a program of instructions stored within the machine.
Different to a calculator because it can make decisions which alter the course of its own program.
What is machine code?
Sequence of instructions built up in RAM memory
What is an OS?
Commecial software which manages all hardware and gives programs convenient access to all services.
What is the Operation code?(opcode)
Specifies WHAT equation to perform
What is an operand?
part which specifies where the relevant data is to be found.
What is the internal BUS?
The way in which the 3 main registers communicate with one another. A set of time shared conducting paths. Only one register at a time can transmit data onto the bus. All other registers 'listen' even if they dont have to take action.
What is inside the MPU?
Numbers held for temporary storage in a set of registers. about 4-10 in a typical MPU.
What is a subroutine?
A section of code that can be 'called' several times by different parts of the main function.
Normally needs some input data (via registers)
Leaves its results in registers or memory locations.
What is an interrupt vector?
A pointer to an ISR (interrupt subroutine)
What is an IRQ
Interrupt request line. When PIA has new data, it asserts a logic 1.
Pros of Subroutines
Error risk reduced
Memory space saved
Simplifies the program layout
Cons of subroutines
Slower to execute than in-line coding due to 'overhead' extra time associated with stack operations
What are jump and branch instructions?
Alter value in program counter to change program flow
What does the Shell do in an OS and what are its advantages?
The user accesses only by the OS shell
It constantly creates manages and destroys discrete processes.
Advantage: user programmes are easily adapted to run on new hardware
What happens to an OS process?
1. Placed in queue
2. In one of 3 states
Running: Has use of CPU
Ready: Could use a CPU if one were available
Blocked: waiting for some event to happen
What is assembly code?
a set of mnemonics to represent opcodes with rules to specify operands.