Test 1- 22nd April Flashcards
What is the CPU?
- Central Processing Unit
- is the electronic circuitry that executes instructions comprising a computer program.
- the CPU performs basic arithmetic, logic, controlling, and input/output operations specified by the instructions in the program
- the processing power of the CPU depends on different characteristics like its clock speed, number of cores and cache size.
What does the CU do?
-Control Unit
- the control unit is in overall control of the CPU
- main job is to execute program instructions by following fetch-decode-execute cycle.
- it controls the flow of data inside the CPU (to registers, ALU, cache) and outside CPU (to main memory and input/output devices)
What does the ALU do?
-Arithmetic Logic Unit
- The ALU does all the calculations
- it completes simple addition + subtraction, compares the size of numbers and can do multiplication and divisions using repeated addition and subtraction.
- It performs logic operations such as AND, OR and NOT
- and binary shifts (computers use binary data)
- it contains the accumulator register.
What does the cache do?
- the cache is a very fast memory in the CPU
- it is slower than the registers but faster than RAM
- It stores regularly used data so that the CPU can access it quickly the next time its needed.
- When CPU requests data, it checks the cache first to see if data is there.
- if not, it will fetch from RAM.
- Cache have a very low capacity and are expensive compared to RAM and secondary storage.
- There are different levels of cache memory- L1, L2, L3.
- L1 is quickest but has lowest capacity, L2 is slower but has more capacity than L1, L3 is the slowest but has the highest capacity.
What is the function of the PC?
- Program Counter
- Holds the memory address of the instruction for each cycle.
What is the function of the MAR?
- Memory address register
- holds any memory address about to be used by the CPU.
- The address might point to data or a CPU instruction.
What is the function of the MDR?
- Memory data register
- holds the actual data or instruction.
- This may have been fetched from memory or be waiting to be written to memory.
What does the accumulator do?
-stores intermediate results of calculations in the ALU
Describe the fetch part of the “fetch-decode-execute” cycle:
Fetch Instructions:
1) Copy memory address from the PC to the MAR
2) Copy the instruction stored in MAR address to MDR
3) Increment (increase) the PC to point to the address of the next instruction, ready for next cycle.
Describe the decode part of the “fetch-decode-execute” cycle:
Decode Instructions:
- The instructions in MDR is decoded by CU.
- The CU may then prepare for the next step, e.g. by loading values into the MAR or MDR.
Describe the execute part of the “fetch-decode-execute” cycle:
Execute Instructions:
1) The instruction is performed.
2) This could be: load data from memory, write data to memory, do a calculation or logic operation, change address in PC or halt program.
Describe the full “fetch-decode-execute cycle”:
Fetch Instructions:
1) Copy memory address from the PC to the MAR
2) Copy the instruction stored in MAR address to MDR
3) Increment (increase) the PC to point to the address of the next instruction, ready for next cycle.
Decode Instructions:
- The instructions in MDR is decoded by CU.
- The CU may then prepare for the next step, e.g. by loading values into the MAR or MDR.
Execute Instructions:
1) The instruction is performed.
2) This could be: load data from memory, write data to memory, do a calculation or logic operation, change address in PC or halt program.
What is a LAN?
-Local Area Network:
- A LAN covers a small geographic area located on a single site
- all hardware for LAN is owned by the organisation that uses it.
- LANS can be wired (with Ethernet) or wireless (WiFi)
Explain some advantages of using LAN:
- Sharing files is easier- network users can access same files.
- They can work collaboratively on files
- You can share the same hardware (like printers) on a LAN
- Internet connection can be shared between every device connected to LAN
- You can communicate with LAN users cheaply and easily, e.g. with instant messaging.
- User accounts can be stored centrally, so users can log in from any device on the network.
What is a WAN?
-Wide Area Network:
- A WAN connects LANs that are in different geographical locations.
- Organisations have to hire infrastructure (communication lines) from telecommunication companies who own and manage the WAN.
- WAN is more expensive to set up than LAN.
- WANs may be connected using fibre optic or copper telephone lines, satellite links or radio links.
- The internet is one big WAN.
