Hardware and Virtual Machines

-It is a large number of computer processors / separate computers connected together …where they are simultaneously performing a set of coordinated computations // collaborative processing. -Network infrastructure -Communicate using a message interface.

-Uses many instruction formats. -Uses variable length instructions. -Makes use of different addressing modes. -Uses a few registers -Has a large instruction set. -Requires complex circuits. -Frequently uses cache. -Instructions (converted to sub-instructions that) may require many clock cycles –Programmable CU

-Uses simple instructions. -Uses fixed length instructions. -Instructions only require one clock cycle. -Uses many registers. -Makes use of pipelining -Hardwired CU

-Pipelining allows several instructions to be processed simultaneously. …therefore this increases the number of instructions completed per unit of time. -Each instruction stage is completed during one clock cycle. -No two instructions can execute their same stage of instruction. -E.g. While one instruction is coded the next is being fetched.

-SISD (Single Instruction Single Data) -SIMD (Single Instruction Multiple Data) -MISD -MIMD

-The emulation of a computer system / hardware and/or software … using a host computer system. -Using guest operating system(s) for emulation.

-Multiple guest operating systems / VMs can be used on the same computer. -Different instruction set architectures can be emulated on a single computer. - A virtual machine can crash without affecting the host machine. There are security benefits // Trying a piece of suspicious software and if it is / has a virus, it will only infect the virtual machine. -Cost savings due to not needing to purchase extra hardware. -Can run legacy applications that are currently incompatible.

-Using a virtual machine means execution of extra code…. -Non-VM installation may not perform in the same way. -Execution speed slower than non-VM system. -Problems in judging actual response times at time of maximum traffic needs fastest possible speed. -Particular hardware may be difficult to emulate . So that hardware can’t be tested using a virtual machine. - A virtual machine may be affected by any weaknesses of the host machine. -Costly and/or complex to maintain / implement / manage

It is used to: -Create/delete virtual machines. -Existing hardware made available to guest OS // hardware emulation -Ensures each virtual machine is protected from actions of another virtual machine.

-The operating system that is actually controlling the hardware

-An operating system run on the virtual machine //OS is being emulated -Guest OS runs under the host OS

-Once the processor detects the existence of an interrupt. -To discard all instructions in the pipelining except for the last instruction in the writeback stage.

-Pipelining is instruction level parallelism. -Execution of an instruction is split into a number of stages. -When the first stage for an instruction is completed, the first stage of the next instruction can start executing. -Another instruction can start executing before the previous one is finished. -Processing a number of instructions can be concurrent/simultaneous.

-There is only one processor. -The processor executes one set of instructions on one set of data.

-Many processors execute the same instruction using different data sets. -Many processors execute different instructions using the same data set. -Many processors execute different instructions using different data sets.

-Split into blocks of code. … that can be processed simultaneously … instead of sequentially. -Each block is processed by a different processor. -Which allows each of many processors to process the different blocks of code independently. -Requires both parallelism and coordination.

-Communication between processors is the issue. -Each processor needs a link to other processors. -Many processors require many of these links. -Challenging topology.

-Only one separate processor -Quad core computer system // processing unit shares the same bus.

-Instruction -Processor -Memory usage -Computer system.

-Guest OS handles the request as if it were running on its own physical machine. -Guest OS handles the request as usual. -I/O requests are translated by the virtual machine software. -Into instructions executable by the host OS -Host OS retrieves the data from the file. -Host OS passes the data into virtual machine software -The virtual machine passes the data to the guest OS. -Guest OS passes the data to the application.