Unit 1 - System Architecture✔️ Flashcards
Three example of input devices?
Keyboard,scanner,microphone
Three example of output devices?
Speakers,display or printer
What is the cpu?
Central processing unit - process input,store data and output results it is the brains of the computer and executes instructions
How did early computers store data to be worked on?
Before 1943 early computers stored data to be worked on in memory - the program was not stored - instructions were input one at a time usings switches and executed one at a time
Who is von Neumann and what did he do?
• In 1943-44, mathematician von Neumann had the idea of storing the program instructions as well as the data in memory
• The stored-program computer was born
How does Von Neumann architecture work?
Program instructions and the data the programs are using are both stored in the same memory - the CPU accesses both instructions and data from the same RAM
Main components of the CPU?
• Control Unit
• Arithmetic-Logic Unit (ALU)
• registers
• Cache
What is the CPU’s register?
• A register is a very fast memory location in the CPU itself
What is a cache?
• Cache is located on the CPU – it is slower to access than registers but faster than RAM
What are the main registers in the CPU?
•Program Counter (PC)
• Memory Address Register (MAR)
• Memory Data Register (MDR)
• Accumulator
What does the program counter do?
holds the address of the next instruction to be executed
What does the memory address register do - MAR?
holds the memory address of the current instruction to be executed, and then the data that it uses, so that these can be fetched from memory
What does the memory data register do - MDR?
holds the actual instruction, and then the data that has been fetched from memory
What does the acccumulator do?
holds the result of an instruction before it is transferred to memory
What does the control unit do?
• The control unit coordinates and controls all of the activities taking place within the CPU
List three things the control unit does?
• It decodes instructions and executes them
• It receives signals from the system clock
• It directs the timing and control of other parts of the CPU
What is the purpose of the arithmetic logic unit - ALU?
The ALU or Arithmetic Logic Unit is where the actual arithmetic operations are done - It also carries out logical operations such as those including AND, OR and NOT
What is the fetch - decode - execute cycle?
Three operations operated by the cpu:
• FETCH – causes the next instruction and any data involved to be fetched from main memory
• DECODE – decodes the instruction
• EXECUTE – the instruction is executed
What does the program counter do?
• The Program Counter holds the address of the next instruction to be executed - increased by 1 as soon as the instruction has been fetched
What is the purpose of the accululator - ACC?
The accumulator (ACC) is where arithmetic and logic results are temporarily stored
Explain in depth what happens during the fetch stage of Fetch,decode,execute cycle?
1) the memory Addresss held in the program counter is copied into the MAR
2) the address in the program counter (PC) is then increased by 1 - the PC now holds the address of the next instruction to be fetched
3)processor sends a signal along the address bus to the memory address held in the MAR
How does the MAR and MDR work together?
The two work together; The MAR knows where to look for data in RAM, the MDR keeps hold of that data until it’s ready to be used by the CPU
Three factors that affect CPU performance?
• Clock speed
• Processor cores
• Cache
What is clock speed?
Cycles per second measured in hertz (Hz) - faster clock speed - faster the instructions are processed
What is a CPU’S number of cores?
The number of duplicate processing units (cores) placed in one CPU
What is a CPU’S cache size?
Memory on the CPU that is faster than RAM but slower than registers and is expensive
Units and values of clock speed?
1 cycle per second eg 1 instruction carried out = 1Hz
• 1 kilohertz (kHz) = 1000 cycles per second
• 1 Megahertz (MHz) = 1,000,000 cycles per
second
• 1 Gigahertz (GHz) = 1,000,000,000 cycles per second
what is clock speed?
1 cycle per second eg 1 instruction carried out = 1Hz
What are the benefits of dual core cpu?
• A dual-core processor has the potential to perform two instructions at the same
• This allows twice as many instructions to be executed - not always taken advantage of by software
What is the cpus cache?
• Cache is a small amount of very fast, expensive memory in the CPU
• It can be accessed faster than regular main memory (RAM)
What is an embedded sysetm?
A computer system that is used to control mechanical or electrical systems - includes RAM,ROM and a cpu
Name three examples of an embedded system?
-microwave
-dishwasher
-satnav
CPU speed of embedded systems?
Typically slow
CPU speed of genreal purpose machines?
Typically very fast
Software of embedded systems?
Has one purpose and cannot install new software
Software of genreal purpose machines?
New software can be installed
Storage of genreal purpose machines?
Programs stored on hard drives
Software of embedded sysetms?
Programs stored on ROM
Reliability of genreal purpose machines?
Runs many programs and may be less reliable and need restarting
Reliability of embedded systems?
Typically very reliable
Why is primary storage needed for Von Neumanns architecture?
primary storage is needed to store programs that are currently running and need to be accessed by the CPU
What is RAM?
Random Access memory - is primary storage that is much faster than a hard drive and stores the operating system and other important operations
List three things RAM stores?
-the operating system
-software currently in use
-the data which the software is using
Is Ram volatile?
Yes - looses data is the power is off
Example of non-volatile storage?
Hard drive - programs and data are permantley stored here and are not lost if the power is off
What is virtual memory?
• Virtual memory is part of the hard drive used as an extension to RAM
Advantages of virtual memory?
• Uses cheap secondary storage on the hard drive
• Prevents error messages saying ‘out of memory’ – the programs and files will still open
Disadvantages of virtual memory?
• Accessing virtual memory is very slow
• To access data, the existing data in RAM needs to be copied to the virtual memory, then data in virtual memory needs to be copied to RAM
What is ROM?
Read only memory - primary storage that does not loose data when the power is off and stores the initial program that is run when the computer is turned on
Two things ROM stores?
-boostrap - inital program which tells the operating sysetm where to find the operating system in the hard drive
-BIOS - stores basic configuration of pc like processor speed
Does RAM an ROM both have a read and write ablility?
No - RAM does but ROM can not write only read
What is secondary storage?
• Secondary storage is not directly accessible by the CPU
• It is non-volatile, meaning it will keep data even if there is no power
•can be external or internal
Three uses of secondary storage?
-programs and data stores on hard drive
-SD cards can be used for additional storage on cameras and phones
-memory sticks to transport data from one place to another
2 examples of secondary storage?
-HDD - hard drive
-SSD - solid state drive
2 examples of offline secondary storage?
-falsh memory eg SD cards
-removable HDD or SSD
List three storage methods?
• Magnetic
• Optical
• Solid State
How does a magnetic storage device work?
• Magnetic: Mechanical parts move over the disks surface to read and write data magnetically, or a drive head reads a magnetic tape
How does a optical storage device work?
• Optical: Lasers read and write data using lig
How does a solid state storage device work?
• Solid State: Data is recorded onto solid memory chips without any moving parts
Describe the features of magnetic disks?
Disk contains circles called tracks which are each divided into sectors - with disk heads mounted on mechanical arms which read and write data
What moves the read/write arm?
Actuator moves the read/write arm
Advantages of magnetic storage?
-Cheap
-large storage capacities
-relativley fast write speed
Disadvantaged of magnetic storage?
-lots of mechanical parts - can make them less durable
Explain how optical storage works?
-data stored as pits and lands pressed into a spiral track circulating outwards from the centre
-laser beam passes over the pits and lands - level of reflection is measured
-from the signal, 0s and 1s can be derived
Advantages of optical storage?
-cheap
-very easily portable
-take up little space physically
Disadvantages of optical storage?
• Less storage capacity compared to other types
• Easily damaged / scratched, requires a CD reader
• Slow write s
Why can blu-ray disks store more then CD disks despite the same physical size?
CD has bigger pits and lands (as red light has a large wavelength) so the smaller blu-ray pits and lands allow it to store more data
What are the basic features of SSD?
•Solid-state disks use non-volatile flash memory to store information
• Very fast read/write speeds as it doesn’t need to wait for a disk to spin to the correct location and an arm to move
• No mechanical or moving parts meaning these disks are very durable
Explain how flash memory works?
• Large electric current used to force electrons through a barrier and trap them on the other side
• They remain on the other side until ‘flashed’ with a new current, hence the name
Advantages of SSDs?
• Highly durable, no moving parts, very fast read/write speeds, no noisy fan or drive arm, faster start up times
Disadvantages of SSDs?
• More expensive than magnetic hard disks, similar storage capacity as magnetic disks
Explain in depth what happens during the decode stage of Fetch,decode,execute cycle?
4) the instruction/data held in that memory address is sent along the data bus to the memory data register (MDR)
5) the instruction/data held in the MDR is copied to the current instruction register (CIR)
Explain in depth what happens during the execute stage of Fetch,decode,execute cycle?
6) the insturction/data held in the current instruction register (CIR) is decoded and the executed in the control unit (Cu) - results are stored in the accumulator (AAC)
7)cycle returns to step one
What is the current instruction register (CIR)?
Holds the instruction that is currently being decoded and executed
What registes are involved in the fetch phase in the cpu?
- PC - program counter
- CIR - current instruction
- MAR - memory address register
- MDR - memory data register
