Section 1 Components Of A Processor Flashcards
State 4 components of the CPU
ALU
Buses
Control unit
dedicated registers
What does the control unit do?
Controls and coordinates data flow between CPU and other devices
Accepts the next instruction, decodes it into several sequential steps eg fetching addresses and data from memory, manages its execution and stores the resulting data back in memory or registers
What are buses made of?
A set of parallel wires connecting 2 or more components of a computer
It typically consists of 8,16,32 or 64 lines
How many buses connect the processor to main memory and what are they called? What directions can data flow through each?
3, the data bus, the address bus, and the control bus
Data and control buses have 2 way signal flow, the address bus is one way
What are the 3 buses known as as a collective?
The system bus
What is the purpose of the control bus? Give some examples (4) of signals it transmits
transmit command, timing and specific status information between system components
Bus Request indicates a device is requesting use of the data bus
Bus Grant indicates the CPU has granted access to the data bus
Clock signals synchronise operations
Interrupt request indicates a device is requesting CPU access
What is a “word” in terms of memory?
Units memory is divided up internally into, as a fixed size group of digits (16,32,64 bits)
What does the data bus transmit?
Data and instructions between system components via a bi-directional path
What does the address bus transmit?
memory addresses of words that are used as operands in program instructions, so the data can be retrieved and sent back to the processor
What is the function of the ALU? What operations can be carried out?
Performing arithmetic and logical operations on the data
ADD, SUBTRACT, MULTIPLY and DIVIDE on fixed or floating point numbers
Boolean logic operations eg. AND, OR, XOR, NOT comparing 2 values
What are registers?
Special memory calls that operate at a very high speed
Results of all arithmetic, logic or shifts are stored here
What is the accumulator register?
One that stores the results of all operations in the ALU
What are 4 registers (minus the ACC) and their function
Program counter (PC) holds the address of the next instruction to be executed which can be the next one in a sequence, or the address to jump to in a branch/jump instruction copied from the CIR to the PC
Current instruction Register (CIR) holds current instruction being executed, divided into opcode and operand
Memory Address Register (MAR) which holds the address of the memory location from which data (or instructions) can be fetched or to which data can be written
Memory data register (MDR) is used to temporarily store data read from / written to memory (AKA memory buffer register)
What is the FDC cycle?
The sequence of operations involved in executing an instruction and can be divided into 3 phases, fetch, decode, execute
Repeats as each inst. is executed.
How are registers used in the fetch execute cycle? (6)
Fetch
1 Address of next instruction is copied from PC to MAR
2 Instruction held at that address is copied to the MDR, and the PC content is incremented simultaneously so it holds the address of the next instruction
3 The contents of the MDR are copied to the CIR
Decode
4 Instruction held in the CIR is decoded. The instruction is split into opcode and operand, where the opcode is used to figure out what hardware to use to execute that type of instruction
The operand holds either
the address of data to be used with the operation, copied to MAR,
the actual data to be operated on, copied to the MDR or the ALU/ACC
Execute
The appropriate instruction /opcode is carried out on the operand
Factors affecting processor performance
Clock speed
Number of cores linked together on a single chip
Amount and type of cache memory
How does clock speed affect processor performance
All processor activities begin on a clock pulse, some may take more than one clock cycle to complete
1 clock cycle = 1Hertz
Greater clock speeds lead to faster instruction execution
What is the typical speed for a PC processor, and how many clock cycles occur per second
2 to 4GHz
2 to 4 billion cycles per second
How does an increase in the number of cores affect processor performance, and how might it not affect speed in the desired way
Each core can theoretically process a different instruction simulatneously with it’s own fetch execute cycle
Software may not be able to take full advantage of more processors
What does it mean when a computer has multiple cores?
when a computer has two or more processors linked together in the same integrated circuit
3 levels of cache?
level 1, extremely fast, small - between 2-64KB
level 2, fairly fast, medium sized - 256KB-2MB
some have a level 3 cache
define cache
A small amount of expensive very fast memory inside the CPU where frequently fetched instructions or data are held
how does amount and type of cache memory affect processor performance?
more allows for more frequently fetched instructions to be accessed faster than from main memory
if too large, searching may take long
if level 1, it’s faster than levels 2 and 3
why does the width of the address bus limit the maximum possible memory capacity of the system?
Each word in memory has its own specific address
When a processor reads a word of data, from memory, it first put the address of the desired word on the address bus
how to calculate maximum memory capacity of a system with the width of an address bus?
2^(no of lines in the bus)
eg an 8 line bus is 2^8
how would a change to the data bus in a processor affect processor performance?
an increase in width would allow for transmitting more characters at a time and more bits per instruction
if a data bus is 16 bits wide, up to what integer can it transmit?
(2^16) -1, or 2 characters
How might a 16 bit word be structured to contain a machine code instruction?
the opcode has 8 bits and so does the operand
the opcode is split into 6 and 2 bits, which can be the basic machine operation and the addressing mode respectively
Defined the stored program concept
Machine code instructions are fetched and executed serially by a processor that performs arithmetic and logical operations
what features are specific to the Von Neumann machine? (3)
1 The same data bus is used to transfer both data and instructions
2 A single address buses used to transfer the addresses of data and instructions
3 The same length is used for all memory, whether it holds data or instructions
what is Harvard architecture? What is it used for?
it’s a computer architecture, with physically separate memories for instructions and data
It is used in DSP systems often
what are 5 examples of digital signal processing (DSP)?
audio/speech signal processing
sonar and radar signal processing
biomedical signal processing
seismic data processing
digital image processing
Why do embedded systems use Harvard architecture?
it can be faster than Von Neumann architecture, because data and instructions can be fetched in parallel, instead of competing for the same bus
This is good for navigation systems, traffic lights and aircraft control systems
compare Harvard and Von Neumann architectures (4)
VN used in conventional processes in PCs, servers and embedded systems with only control functions. H is used in DSP,communication systems, and audio speech and image processing systems.
VN data and programs share the same memory, but in H they’re held in separate memories
VN uses one bus to transfer data/nstructions, but in H parallel data and instruction buses may be used
VN programs can be optimised but in H programs tend to be large
what is contemporary processor architecture?
Includes aspects of both architectures
Features of CISC, adv and disadv
The machine hardware has complex instructions, and these can take multiple clock cycles to be executed
A: Short SC means the compiler only has a little bit of work to do to translate high-level language statements into machine code
The code is relatively short, so very little RAM is required to store the instructions
D: many specialised instructions are built into the hardware, even though 20% of them were used in the average program 
features of RISC, advs and disadvs
it uses simplest instructions which each take one clock cycle to be executed
A: as each instruction takes the same amount of time (1 clock cycle) pipelining is possible, so the instructions would execute at least as fast as a single CISC instruction
D: the compiler has to do more to translate high-level code into machine code
More RAM is required to store the machine code instructions
what is CISC still used for?
microcontrollers and embedded systems
what does a coprocessor system involve?
an extra press processor is used to supplement the functions of the primary processor
it may be used to perform Floating Point arithmetic, graphics processing or digital signal processing
It has only a limited range of instructions
what is meant by a parallel system?
Systems with multi core CPUs that are able to distribute workloads across multiple CPU cores
benefits of a multicore system and an example?
they distribute workload across multiple CPU cores achieving higher performance
For example, browsers may use all four CPUs on a phone when tabbed browsing is used
Two types of barcodes
linear barcodes
2D barcodes such as the quick response code (QR code)
four types of barcode readers
Pen-type readers, laser scanners, CCD readers, and camera based readers
advantage and disadvantage of pen type readers
They are the most durable type of scanner because of the simple design
They useful for very low volume scanning applications
However, they have to come into direct contact with the barcode to read it
Where are laser scanners most commonly found?
In the in-counter units in supermarkets
where are camera based readers used?
age verification by scanning individual driving licenses
Event ticketing where tickets can be issued electronically then scanned off a phone screen
Phones can scan a QR code which can display a catalogue of movies or DVDs or play an MP3 when scanned
Disadvantage and advantage of using a CCD digital camera for scanning barcodes?
Power consumption is extremely high
but they are more reliable as the technology has been used for years
List 8 output devices
LCD monitors, OLED screens, laser printers, inkjet printers, 3-D printers, speakers, multimedia projectors and actuators
3 Advantages of OLED screens over LCDs
they made of plastic
they are much thinner
they are brighter and need no backlighting, so they consume less power which translates to longer battery life in portable devices
When to use a laser printer and when to use an inkjet printer
use a laser one where a lot of text needs to be printed and an inkjet printer to produce high quality photograph images
what are actuators? Give 3 examples where they’re used
they are motors that are commonly used in conjunction with sensors to control the system.
For example, opening a window or valve, stopping or starting a pump and turning a wheel
characteristics of magnetic storage
it uses rotating platter, coated with magnetic material and iron particles are polarised to become either north or south state south states which represents zero and one
The disc is divided into tracks in concentric circles and each track is subdivided into sectors
data is to or written to disc as it passes under the drive head
Hard disk disadvantages
not portable
prone to breaking down
Hard disk advantages
Large capacity so suitable for desktop
How does an optical disc work?
it uses a high powered laser to burn sections on the surface, making them less reflective
a lower power laser is used to read the disc by shining light onto the surface on a sensor is used to measure the amount of light reflected back
how does a read only disc work?
During manufacture, the CD has pits and lands on its surface
at the point where a pit starts or ends light is not reflected so well, so reflective and non-reflective areas are read as ones and zeros
what is RAM used for?
it’s used to store programs and data that are currently being used
it’s volatile
What is ROM used for?
it’s used to hold information that needs to be permanently in memory, for example, the BIOS, and in embedded systems where the software doesn’t change
Why is there a need for virtual storage?
storing files and applications on local servers at the same physical site as they are used is becoming less common due to security threats
Advantages of using virtual storage
Reduced hardware costs
improved reliability and performance
the flexibility to scale storage requirements up and down as needs change over time
Disadvantages of virtual storage
you will need a full Internet connection to access all of your files
You may need a backup plan in place with your storage provider to keep your data safe in the event of hardware failure
there can be an increasing fee, depending on the volume of storage used
there may be less functionality of the files
