Chapter 15: Hardware And Virtual Machines Flashcards
Explain RISC, 4 - 7 marks
Reduced Instruction Set Computers
- Uses simple, fixed-length instructions, fewer instruction formats & addressing modes
- Instruction only require one clock cycle
- Uses many general purpose registers and a hard-wired CPU
- Makes use of pipelining - executes instructions in parallel, where the output of one instruction is the input of the next
- Makes more use of RAM than cache
- Design emphasis is on software
- Processor chips require fewer transistor
What is Pipelining (1 mark)
Allows several instructions to be processed simultaneously
- Pipelining is used to increase instruction that is passed through the F-E cycle
Process of Pipelining
Instructions are divided into subtasks
- Instruction fetch
- Instruction decode
- operand fetch
- opcode
- result store
Each subtask is completed during one clock cycle
No 2 instructions can execute at their same stage at the same clock cycle
- The second instruction begins in the second clock cycle, while the first instruction has moved on to its second subtask etc.
Explain CISC - 5 marks
Complex Instruction Set Computers
- Uses many instruction formates
- Makes use of different addressing modes
- Uses few registers and a programmable CPU
- Multi-cycle: Instruction may need many clock cycles
- Requires complex circuits and frequently uses cache (uses less RAM)
Interrupt Handling in both RISC and CISC
- Process detects an interrupt at the start/end of FE cycle
- The program is paused and the contents of the registers are stored in a stack
- Appropriate ISR routine is called and executed
- After the interrupt has been serviced/ resolved the data are restored from stack to the registers, returning them to their original status
Effect of Pipelining
This only in RISC
- Adds additional complexity: Since pipelining means instructions are processed at the same time, if theres an interrupt, it would be messy
- All currently operating instructions are discarded except for the last one - the interrupt handling routine is applied to the remaining instruction
—> the last one meaning the one at the last stage of its process
- Once the interrupt has been serviced the processor can restart with the next instruction in the sequence
4 Different Computer Architectures
SISD, SIMD, MISD, MIMD
Explain SISD
Single Instruction Single Data
- One processor executes a single instruction using the same data set
- Data is taken from one single source and only a single instruction is performed on it
Explain SIMD
Single Instruction Multiple Data
- One single instruction on multiple different data sets simultaneously
- Instructions can be performed sequentially, using pipelining
Parallel computers with multiple processors
Explain MISD
Multiple Instruction Single Data
- Multiple instructions are used on the same set of data
- Each processor works on the same data set independently
- Parallel computers with multiple processors
Explain MIMD
Multiple Instruction Multiple Data
- Many processors that operate independently
- Any processors can execute different instructions on different data sets
Explain Massively Parallel Computers
- Its a kind of network infrastructure
- a large number of computer or separate computers connected together -> simultaneously performing a set of coordinated computations
- communicates using a message interface (send messages between each other)
Virtual Machines - Define/ Explain (2 marks)
They are an emulation of a computer using a host computer system
- uses guess OS for emulation
Benefits of Virtual machines (2 - 4 marks)
- Cost Saving - new system can be tried on virtual machines without needing to buy new hardware
- Security - if a virus is downloaded on the emulated system, it only affects the VM not the host
- Can emulate old software on a newer system using compatible guest OS
Limitations of Virtual Machines
- The cannot emulate some hardware
- Using VM puts more load on the host computer system - makes the host less efficient, increases processing time and uses more RAM
- Increases the maintenance expenses as both host and VM must be maintained
(And more)
Host OS (relating to virtual machines)
- The normal OS used by the host machine
- Has control of all the resources of the host machine/ computer
- Provides UI to operate the VM
- Actually runs the VM
Roles of Guest OS
- OS that runs within VM
- Controls the virtual hardware and software during emulation - access actual hardware through host
- Provides UI for the emulated software
Half Adder/ Full Adder
