1.1 The characteristics of contemporary processors, input, output and storage devices
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What is a processor?
seen as ‘the brain’ of the computer -executes instructions allowing programs to run
What is the function of the ALU
arithmetic and logic unit- completes the arithmetical and logical operations
What is the function of the control unit? Give examples (3)
directs operations inside the CPU -controls and coordinates activities of the CPU -manages flow of data between CPU and other devices -decodes instructions
What are registers? What do they do?
-small memory cells which operate at very high speeds -used to temporarily store data such as arithmetic, logical and shift operations
Name all the registers (5)
-program counter (PC) -accumulator (ACC) -memory address register (MDR) -memory data register (MAR) -current instruction register (CIR)
What is the PC used for?
program counter (PC) - holds address of the next instruction to be executed
What is the ACC used for?
accumulator (ACC) - stores results from calculations
What is the MAR used for?
memory address register (MAR) - holds address of a memory location that has been fetched or data that needs to be written
What is the MDR used for?
memory data register (MDR)- temporarily stores data that has been read or data that needs to be written
What is the CIR used for?
current instruction register (CIR) - holds current instruction being executed, divides it into operand and opcode
What is the data bus used for?
-a bi-directional bus (data/bits can be carried in both directions) transports data and instructions between components
What is the address bus used for?
transmits the memory addresses specifying where data is to be sent to or retrieved from
What is the control bus used for?
-a bi-directional bus (data/bits can be carried in both directions) transmits control signals between internal and external components
What type of signals are given out by control buses? (6)
-bus request: shows that a device is requesting the use of the data bus -bus grant: shows that the CPU has granted access to the data bus -memory write: data is written into the addressed location using this bus -memory read: data is read from a specific location to be placed onto the data bus, -interrupt request: shows that a device is requesting access to the CPU -clock: used to synchronise operations
In the decode phase of the FDE cycle, what is the instruction divided into? Where?
opcode and operand -in the CIR
What do we mean by opcode?
a section of the instruction used to determine what type of instruction it is and what hardware is needed to execute it
What do we mean by operand?
a section of the instruction which tells us the address of where the operation is performed
What is the FDE cycle?
fetch-decode-execute cycle is the sequence of operations that are completed by the cpu to execute an instruction
What happens during the fetch phase of the FDE cycle? (4)
-address from PC is copied to the MAR -instruction held at that address is copied to MDR via data bus -simultaneously, the contents of the PC increment by 1 -value held in MDR is copied to the CIR
What happens during the decode phase of the FDE cycle? (1)
the contents of the CIR are split into operand and opcode
What happens during the execute phase of the FDE cycle? (1)
the opcode is executed on the operand
What is pipelining?
the process of completing the different stages of the FDE cycle simultaneously
What are some limitations of pipelining? (2)
-programs with lots of branched instructions may not benefit from the effects of pipelining -some instructions may need to be flushed if the instruction branches off
What are the different types of computer architecture? (3)
-von neumann -harvard architecture -contemporary processing