What is the CPU?
The CPU executes programs, which are stored as
numbers representing Machine Language Instructions
What is the Control Unit (CU) and what cycle does it preform?
Control Unit – controls all parts of the computer system. It manages the four basic operations of the Fetch Execute Cycle.
What does the Arithmetic Logic Unit (ALU) do?
The ALU must perform the command, performing Arithmetic (+,*,,/) or Logic (and, or,…) operations. The result of the operation is placed in the ACCUMULATOR (a CPU register). Then the CU might send a result back to the RAM.
Stages of data retrival
- The Memory Address Register contains the address (location) of a byte in the memory.
- This is transmitted over the Address Bus.
- After that the RAM finds the data and sends it back over the Data Bus,
- and the value is stored in the Memory Data Regiter.
CPU and Memory diagram
What types of registers are there?
MIMAP
- Memory Address Register
- Instruction Register
- Memory Data Register
- Accumulator
- Program Counter
What does the Program Counter do?
Program Counter: Stores the address of the next instruction
What does the Memory Address Register do?
Memory Address Register: Stores the address in memory that is to read or written.
What does Memory Data Register Do?
Memory Data Register: Stores the data in memory that has been read or is to be written.
What does the instruction register do?
Instruction Register: Stores the current instruction being processed.
What does the Accumulator do?
Accumulator: A set of general purpose registers used for storing temporary intermediate results of the CPU’s calculations.
What is done in the Fetch Phase?
- The PC (Program Counter) stores the address of the next instruction in memory.
- The contents of the PC are copied to the MAR and the PC is incremented.
- The address is put onto the address bus.
- The data at that address is read into the MDR.
- The data returns on the data bus.
What is done in the Decode Phase?
- The instruction carried by the MDR is copied to the IR (Instruction Register)
- The instruction is translated into a format that the ALU can understand.
What is done in the Execute Phase?
- The ALU carries out the operation, e.g. ADD, MUL, CMP, JMP, STO, etc.
What is done in the Store Phase (optional)?
This is almost exactly the same as the Fetch phase, except that the control bus carries a “write” signal instead of a “read” signal. Therefore, instead of reading the data stored at the MAR address into the MDR, the data stored in the MDR is written to the location at the MAR address.
What is an operating system?
Software that controls the execution of programs and that may provide services such as resource allocation, scheduling, input/output control, and data management.
Functions of an Operating System?
- A collection of programs
- Input/Output (IO) control
- File management
- Software/hardware interface
- Memory management
- User interface
- Scheduling
- Program execution control
- Security
What is primary memory?
RAM and ROM
What is secondary memory/storage?
- Disk storage
- Magnetic tape
- USB flash drives
- SSD
Difference between RAM and ROM?
- RAM: Random Access Memory. Holds data and instructions from running programs.
- ROM: Non-volatile memory, used to hold the operating system’s bootstrap loader (small start-up program) or BIOS.
- ROM cannot be modified
What are registers (memory)?
Smallest, fastest memory, used to hold data that the CPU is
currently working.
What is the cache?
Small, fast memory, used to hold very frequently used data.
Operating system memory management tasks?
- Multi-tasking environment: keeping the memory space of each process safe from other running processes (see Security)
- Multi-user environment: keeping the memory space (primary and secondary) of each user safe from other users (see Security)
- Allocating and deallocating memory for each process
- Paging: Dividing virtual memory up into equal- sized blocks (pages). Paging allows OSs to allocate non-contiguous chunks of memory to the same process, thus reducing fragmentation problems
- Virtual memory: The use of secondary memory as if it were primary memory. By creating virtual memory, the OS make it easier for programs to reference memory because they don’t need to worry about the complications of the underlying physical structure of memory and disk (another example of abstraction)
Types of applications?
- Word processor: Text document management
- Spreadsheet: Mathematical and financial calculations
- Database: Organisation of information
- Email: Electronic mail
- Web browser: Viewing HTML pages
- Graphics processing: Editing, cropping and enhancing images
- Computer-Aided Design (CAD): Creating and editing designs for engineering or manufacturing
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