Computer Systems Flashcards
Hardware
- The physical components of a system
- Includes both internal and external components
Software
- The name given to program code
- Comprised of sequences of instructions that are executed in order to perform a task
Types of software
- Application software
- System software
Application software
- Programs that complete a specific task for the user
- e.g web browsers, spreadsheet software, word processors
System software
Software that operates, controls and maintains the computer and its components
Types of system software
- Operating systems
- Utility programs
- Library programs
- Translators
Operating system
- Allows the user to control the computer
- Provides a virtual machine to hide the true complexity of the computer from the user
- Manages and controls access to the computer’s resources (memory management, processor scheduling, handling interrupts)
Utility programs
Used to complete housekeeping tasks like:
- Data backup
- Defragmenting hard drives
- Data compression
- Encryption
Library programs
- Contain helpful, frequently used programs
- Must be imported within the program code
- Simplifies the process of application development
Low level languages
- Are processor specific
- Directly manipulate the processor
- Are difficult to code with and are prone to errors
Types of low level languages
- Machine code
- Assembly code
Machine code
- Uses only the binary digits 0 and 1
- Programs are long and very difficult to code and debug
Assembly language
- Developed to simplify the coding process
- Mnemonics are used in place of binary instructions
- Each instruction has a 1-to-1 correlation to a machine code instruction
High level langauges
- Are not platform specific
- Must be translated into machine code by a compiler or interpreter
- Uses English instructions and mathematical symbols
- Contains built in functions, variables, indentation and commenting
Types of program translator:
- Assemblers
- Compilers
- Interpreters
Assemblers
- Translate assembly language into machine code
- Are platform specific
- Translation is quick and straightforward
Compilers
- Translate high-level languages into machine code
- Are platform specific
- Takes the high-level program as their source code and checks for errors line-by-line
- Translates the entire program at once if the source code is error free
Interpreters
- Translate high-level languages into machine code
- Translate line by line, using procedures to translate each kind of program instruction
- Both the interpreter and the source code must be present for a program to be ran
Components of the computer
- Processor
- Main memory
- Address bus
- Data bus
- Control bus
- I/O controllers
Processor
- Executes program instructions in order to run applications
- Contains an ALU, CU and numerous registers
Main memory
- Includes RAM and ROM
- Stores program instructions and frequently used data
Buses
- A series of parallel wires that connect internal components of a computer system
- Allows for the transfer of signals between components
Bus width
- The number of parallel wires
- Has a direct relationship with the number of bits that can be transferred simultaneously
Address bus
- Used to transport memory addresses
- Specifies where in memory data is be sent to or retrieved from
- Each wire added doubles the number of addressable memory locations
Data bus
- Sends data and instructions to and from the different components of the computer system
- Increases the width increases the volume of data that can be transferred at one time
Control bus
- Used to carry control signals that regulate the operation of the computer system
- Controls the computer’s clock signal
I/O controllers
Hardware that control the communication of data between the processor and external hardware devices
Harvard architecture
- The processor uses 2 separate main memory locations (1 for data, 1 for instructions)
- Each piece of main memory can have different characteristics
- Used in embedded systems
Von Neumann architecture
- Both instructions and data are stored together in the same memory
- Buses are shared for fetching both instructions and data
- Used in general-purpose computer systems
Stored program concept
- Machine code instructions are stored in main memory
- Instructions are fetched and executed serially
- By a processor that performs arithmetic and logical operations
Advantages of the stored program concept
- Allows for one set of instructions to be switched out for another
- Allows modern computers to run numerous different applications
- Contents of a memory location can be interpreted as instructions or data
Arithmetic logic unit
Performs arithmetic (+, -, etc) and logical (AND, OR, etc) operations
Control unit
- Responsible for controlling the various parts of the processor by coordinating the data flow and generating control signals
- Controls the fetch-execute cycle
Registers
- Small storage locations used to hold data temporarily
- High read and write speeds
Types of registers
- General purpose registers
- Special purpose registers
General purpose registers
Registers that are used as storage for any data required by instructions during execution
Special purpose registers
Registers that are assigned to store specific information
Types of special purpose registers
- PC
- CIR
- MAR
- MBR
- SR
Program counter
Holds the memory address of the next instruction to be executed in the fetch execute cycle
Current instruction register
Holds the instruction that is currently being executed by the processor
Memory address register
Stores the memory address of a memory location that is to be read from or written to
Memory buffer register
Holds the contents of a memory location that has been read from or data is to be stored
Clock
- Generates a timing signal of regular size and frequency
- Used to synchronise communication between components of the processor and the rest of the computer system
Fetch-execute cycle
- A continuous cycle performed by the processor to execute programs
- Consists of 3 stages (Fetch, Execute, Decode)
Fetch
The next instruction to be executed is retrieved from main memory:
- The content of the PC is copied to the MAR
- The content of the MAR is transferred to main memory by the address bus
- The instruction is sent from main memory to the MBR by the data bus
Decode
The fetched instruction is decoded:
- The contents of the CIR is decoded by the CU
- The decoded instruction is split into the opcode and operand
Execute
The instruction is carried out:
- Any additional data not in the registers are fetched
- The instruction is carried out
- The results are stored in GPR or main memory
Interrupt checking
- The processor checks for interrupts between each cycle
- The content of the SR is checked for changes
- A change could signal the occurrence of an interrupt
Interrupt
Signals sent to the processor by another part of the computer requesting the attention of the processor
Processor instruction set
- The group of instructions that a processor can carry out
- Each processor has a unique instruction set with instructions that may not be compatible with other processors
Processor instructions
- Stored in machine code
- Consist of the opcode and operand
Opcode
The type of operation to be carried out
Operand
The pieces of data on which the operation is performed
Immediate addressing
The operand specifies the actual value to be used
Direct addressing
The operand specifies the memory address where the value to be used is stored
Logical shift
- An operation performed on binary numbers
- Involves shifting all the bits a specified number of positions
- The result is a number that has been halved/doubled a specified number of times
Vectored interrupt method
- The processor stops executing the current program and places the cont of its registers on the system stack
- The processor loads the appropriate interrupt service routine
- Once the interrupt has been handled the processor restores the volatile environment
Factors affecting performance
- Number of cores
- Cache memory
- Clock speed
- Word length
- Bus width
Number of cores
- Each core can perform its own fetch-execute cycle
- Different applications can be allocated different cores
Cache memory
- A small amount of incredible fast memory
- Stores frequently accessed information
- More cache memory allows more time to be saved fetching data and instructions
Clock speed
- The frequency of pulses generated by the system clock
- A higher frequency allows for more fetch-execute cycles to be performed
Word length
- A word is a group of bits that is treated as a single unit by the processor
- Larger word lengths allow for more bits to be transferred and manipulated at once
Bus width
- A larger width is achieved by adding more parallel wires
- A wider address bus allows for more addressable memory
- A wider data bus increases the volume of data that can be transferred at once
