computer systems.
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104 Terms
What does the CPU stand for?
Central Processing Unit.
What is the function of the CPU?
The function of the CPU is to process data + instructions by carrying out the FDE cycle.
What are the components of the CPU?
The components of the CPU are the CU, clock, ALU, registers, buses + cache.
What does the CU stand for?
Control Unit
What is the function of the control unit?
The function of the control unit is to…
…decodes instructions (in the CIR)
…issue signals that co-ordinate the other components
…control the flow of data around the system.
What is the function of the clock?
The function of the clock is to send out a regular electrical pulses to synchronise the computer’s hardware components + regulate the number of FDE cycles per second.
What does the ALU stand for?
Arithmetic Logic Unit.
What is the function of the ALU?
The function of the ALU is to perform arithmetic + logical operations.
What are the registers in the CPU?
The registers are small amounts of high-speed memory contained within the CPU.
What is the function of the registers?
The function of the registers is to store small amounts of data that are required during processing, e.g. the address of the next instruction to be executed.
What are the names of the registers?
The names of the registers are the PC, MAR, MDR, CIR + ACC.
What does the PC stand for?
The PC stands for the Program Counter.
What is the function of the PC?
The function of the PC is to store the memory address of the next instruction to be fetched from primary memory.
What does the MAR stand for?
The MAR stands for Memory Address Register.
What is the function of the MAR?
The function of the MAR is to store the memory address of the current instruction that is to be fetched from primary memory or the memory address to which data is to be transferred to.
What does the MDR stand for?
The MDR stands for the Memory Data Register.
What is the function of the MDR?
The function of the MDR is to store the data found at the memory address stored in the MAR or data which is to be transferred to primary memory.
What does the ACC stand for?
The ACC stands for the accumulator.
What is the function of the accumulator?
The function of the accumulator is to store the data being processed + the results of processing.
What is the function of the buses?
The function of the buses is to transfer data + instructions between different components in the CPU.
What is cache?
Cache is a small amount of high-speed RAM built directly within the processor.
What is the function of cache?
The function of cache is to temporarily store data + instructions that the processor frequently uses as the transfer of data to and from the cache is faster than it is from RAM.
Why is cache memory small in size?
It is more expensive to build than RAM because of its high-speed performance.
What are the two types of cache?
L1 and L2 cache.
What are the functions of the two types of cache?
L1 cache is used to store data + instructions that are used the most frequently because it transfers data very quickly but has an extremely small size.
L2 cache is used to store data + instructions that are needed less frequently because its rate of data transfer is slower but has a larger capacity.
What is Von Neumann architecture?
Von Neumann architecture is the description of the processing architecture that all CPUs use
What are the key features of Von Neumann architecture?
The key features of Von Neumann architecture are…
…data + instructions are stored as binary digits
…data + instructions are stored in primary memory
…instructions are fetched from memory serially - one at a time
…the processor decodes + executes one instruction before fetching the next instruction
…the cycle continues until no instructions are left.
What are the steps involved in the fetch-decode-execute cycle?
The memory address stored in the program counter is copied in to the MAR.
Then, the memory address stored in the program counter is incremented by one so that it holds the memory address of the next instruction to be fetched.
The processor then sends a signal along the address bus to the memory address stored in the MAR.
The instruction/data stored in the memory address is sent along the data bus to the MDR.
The instruction/data is copied from the MDR into the CIR.
Finally, the instruction/data stored in the CIR is decoded + executed and the results are stored in the ACC.
The cycle then returns to step 1.
What additional steps may be taken (in the fetch-decode-execute cycle) if the instruction is to transfer data stored in the ACC, back to primary memory?
The memory address where the data is supposed to be transferred to is copied into the MAR. Then the data stored in the ACC is copied into the MDR using the data bus and transferred to the specified memory address along the address bus.
How does increasing clock speed improve CPU performance?
An increased clock speed increases the number of pulses per second. This increases the number of fetch-decode-execute cycles that a completed and the number of instructions processed.
How does increasing cache size improve CPU performance?
By increasing cache size, more frequently used instructions can be stored in the cache which reduces the amount of instructions that need to be fetched from RAM.
How can increasing the number of cores improve CPU performance?
By having more cores, the CPU can process more instructions as each core is capable of completing its own fetch-decode-execute cycles.
What is a general purpose computer?
A general purpose computer is a computer that is designed to perform many tasks, known as applications.
What are some examples of general purpose computers?
PCs, tablets, smartphones + gaming consoles.
How is data processed in a general purpose computer?
What is an embedded system?
An embedded system is a computer designed to perform one or a few select tasks.
What are some examples of embedded systems?
Central heating systems, domestic appliances, digital watches, GPS systems + fitness trackers.
What are the advantages of embedded systems over general purpose computers?
Embedded systems…
…are cheaper to design + build because of their limited number of functions
…require less power
What is hardware?
Hardware refers to the physical components of the computer, i.e. the CPU.
What is software?
Software refers to the programs that run on a computer.
What is system software?
System software are programs that control a computer system. They…
…control the computer’s hardware + peripherals
…allow applications to run
…provide an interface for the user to interact with
…maintain the system
What is an operating system?
An operating system refers to the software that manages the hardware and software in a computer system.
What are the functions of an operating system?
Operating systems have many functions:
controlling hardware components
providing a platform for software to run on
providing a user interface
multitasking facilities
managing the computer's memory
managing peripherals
managing files
managing users
What are some examples of operating systems?
Microsoft Windows, Apple OS X, Linux, Android and IOS.
What is a user interface?
User interface refers to the software that allows a user to interact with a computer.
What are the 3 types of user interface?
graphical user interface (GUI) - sometimes known as WIMP (Windows, Icons, Menus, Pointers) interface
mobile user interface (Mobile UI)
command line interface (CLI)
What is a GUI?
A graphical user interface features a desktop where everything is displayed. Objects (apps, hardware + files) are represented by icons. Applications run in windows and their features are accessible through the use of menus.Users interact with the interface using a mouse + on screen pointer.
What is the difference between a GUI + Mobile UI?
Instead of using a mouse and an on screen pointer, Mobile UIs use touch to interact with them.
What are pros and cons of a GUI?
An advantage of a GUI is that they are easy to use. However, a disadvantage is that they require a lot of processing power.
What is a CLI?
A common line interface is a text-based interface that users can use to control the computer by typing in commands.
What are the pros and cons of CLI?
An advantage of using CLIs is that they require little processing power. However, a disadvantage is that they are difficult to use.
What is utility software?
Utility software refers to the software that helps maintain the computer system.
What are the 4 types off utility software?
encryption software
defragmentation software
data compression software
backup software
What is encryption software?
Encryption software is a type of utility software that alters the contents of files so that they can only be read by authorised users.
What is defragmentation software?
Defragmentation software is a type of utility software that rearranges fragmented files so they run contiguously, which decreases the read/write time and thereby improves computer performance.
What is data compression software?
Compression software is a type of utility software that reduces the size of a file stored on secondary storage, which increases capacity.
What is backup software?
Backup software automatically makes a backup at a scheduled time of the day so that if data is lost, it can be retrieved from the backup.
What is a full backup?
A full back up involves making a copy of every file on a computer system which requires a lot of storage space + time.
What is an incremental backup?
An incremental backup only makes a copy of new or edited files.
What are the two types of primary memory?
ROM + RAM
What is ROM?
Read-only memory is non-volatile primary memory - the data stored in this type of memory is kept even when the computer is switched off.
What is the purpose of ROM?
ROM is used to store instructions that the computer needs to run as it is read-only - it can only be read from, not written to - and non-volatile.
What is the BIOS?
The Basic Input Output System is a program stored in ROM that runs as soon as the computer is switched on - it checks that the hardware is functioning correctly, then runs a different program (boot up program) that loads the operating system from the hard drive into the RAM.
What is RAM?
Random access memory is volatile primary memory - the data stored in the RAM is lost once the computer is switched off + can be stored and accessed from any location within the memory.
What is the purpose of RAM?
RAM stores data + instructions currently in use (i.e. any open programs that are running) as the data stored within it can be read from and written to, allowing the user to close + open different programs (change the contents).
What is virtual memory?
Virtual memory is a segment of secondary storage used temporarily as RAM.
What is the purpose of virtual memory?
Virtual memory is used when the computer has no more available RAM.
What is swapping?
Swapping is when data stored in the RAM (that is currently not in use) is transferred to virtual memory. When the data is needed again, any other currently unused data is transferred to virtual memory before the original data is transferred back to RAM.
Why does virtual memory make the computer run slower?
The processor has to wait as data is swapped between virtual memory + RAM, which takes a long time as secondary storage devices have slower access times than RAM. However, this problem can be avoided by increasing the size of RAM which reduces the need for virtual memory.
What is secondary storage?
Secondary storage is non-volatile memory external to the CPU, which is used for the long-term storage of programs + data.
What are the 3 types of secondary storage device?
magnetic storage devices, such as hard disk drives
optical storage devices, such as CD, DVD and Blu-ray discs
solid state storage devices, such as solid state drives and USB memory sticks
What do demagnetised + magnetised sections of a hard drive disk represent?
A magnetised section represents a binary '1' and a demagnetised section represents a binary '0'.
How is data read from a magnetic storage device (hard drive disk)?
As the disk spins, the read/write head checks whether a section is magnetised or demagnetised.
How is data written to on a magnetic storage device (hard drive disk)?
As the disk spins, the read/write head magnetises or demagnetises a section of the disk that is spinning under it.
What are lands + pits?
Lands are the flat areas of a disc whilst pits are the hollow areas.
What do the lands + pits of optical storage represent?
The lands represent a binary '1' because they reflect the laser, whilst pits represent a binary ‘0’ because they don’t reflect the laser.
How is data written to an optical storage device?
A laser is shined onto a disc and burns pits.
How is data read from an optical storage device?
As the disc is spinning, a laser distinguishes between the land + pits on the disc based on how each section reflects the light.
What are the different types of optical media?
ROM media have data pre-written on them which cannot be overwritten. Music, films, software and games are often distributed this way.
R media are blank and can only be written to once, but read many times. Copies of data are often made using these media.
RW works in a similar way to R, except that the disc can be written to more than once.
What is machine-code?
Machine-code is a low level language which represents how the computer hardware understands instructions + represented by binary/hexadecimal.
What is a high-level language?
A high-level language is a computer programming language used to write programs that are easier for humans to understand.
What are examples of high-level languages?
Some examples of high level languages are:
Python
Java
C++
C#
Visual Basic
JavaScript
What is a low-level language?
This is a computer programming language which closely represents machine-code.
What are the 2 types of low-level language?
Assembly language + machine code.
What is an advantage + disadvantage of machine code?
Advantage: Machine-code allows programmers to do things that may not be possible using high-level languages.
Disadvantage: Machine-code is difficult for humans to understand, learn, program in or debug.
What does assembly language use to write instructions?
Assembly language uses mnemonics to write instructions, making it easier to program in + understand than machine-code.
What is an opcode?
The operation code is the instruction that is executed by the CPU in machine code.
What is an operand?
The operation command is the data that is manipulated by the CP, according to the opcode.
What is source code?
Source code is code written in a programming language, thus not understood by the computer.
What is object code?
Object code is code that is understood by the computer.
What is the purpose of translators?
Translators translate source code into object code so that the computer can run the program.
What is an assembler?
An assembler is a type of translator that translates assembly language into machine-code.
What is a compiler?
A compiler is a type of translator that translates all of the source code into object code in one go (compilation).
What are the advantages + disadvantages of compilers?
Advantages:
Compiled programs run quickly as they have already been translated.
Compiled programs can be supplied as an executable file which is ready to run.
Compilers optimise code which make it run quicker + take up less memory space.
Disadvantages:
The source code must be re-compiled every time the programmer changes the program.
Source code compiled on one platform will not run on another because the object code is specific to the processor's architecture
What is an interpreter?
An interpreter is a type of translate that translates source code one instruction at a time (interpretation).
What are the advantages + disadvantages of interpreters?
Advantages:
Instructions are executed as soon as they are translated
Interpreters require less available memory as instructions are not stored for later use.
Errors can be identified quickly because once an error is found, the program stops + identifies the user where the interpretation has failed.
Disadvantages:
Interpreted programs run more slowly as the processor has to wait for each instruction to be translated before it can be executed.
When using an interpreter, the program has to be translated every time it is run.
Interpreters do not produce an executable file that can be distributed.
Interpreters do not optimise code - the translated code is executed as it is.
What is an IDE?
A integrated development environment is a series of tools that help a programmer to write error-free, maintainable code.
What are editors?
Editors are software which allow programmers to write and edit code. They usually offer facilities like:
automatic line numbering
colour coding
auto-correct
auto-suggestion
auto-indent
These features help improve the readability of code but usually don’t help in identifying errors.
What is an RTE?
A runtime environment is special software that allows a program to run on a computer even if it is not designed to run on it.
What are debugging tools?
Debugging tools are tools that help programmers identify + fix errors:
breakpoints enable a program to be paused at predetermined points
variable tracing lets the programmer see the changing values of variables as the program runs
Both of these tools allow the programmer to evaluate whether the program is functioning as expected.
error trapping shows exactly where a syntax error has occurred, or at which line in a program an error is generated.