11866860
| Question | Answer |
| What is I/O speed | Data rate measured by bit per second |
| State one input, output and one I/O device | Keyboard is input and has a data rate of 0.01 laser printer is a output and has a data rate of 100 Wireless network is a I/O with a data rate of 50,000 KB/s |
| What is the CPU and i/O speed mismatch ? and why is there a mismatch> | 1 GHz microporcessor with 1 billion load/store insturctions per second, 4 million KB/s data rate I/O device data rates range from 0.01 to 200,000 KB/s Input: device may not be ready to send data as fast as the processor loads it Output: device not ready to accept data as fast as processor stores it |
| What do you need to make I/O work | Variety of peripherals, delivering different amounts of data at slower speeds than CPU and RAM Need to connect lots of devices, control them, and transfer data and a way to present them to user programs Need a I/O controller (interface) |
| Draw a I/O controller diagram | |
| What are the functions of the I/O controller | Recognizes messages from devices addressed to it & accepts commands from the CPU Provide buffer to hold data from memory until it can be transferred to device Copy this data to device Provide necessary registers and control for a direct memory transfer Control device and communicate with CPU |
| What is isolated I/O | When procesors have special input and output insturctions to access I/O device |
| What is memory-mapped input/output? | Users load for input, store for output used by MIPS |
| State the three techinques to make I/O work | 1. Programmed I/O (cpu controlled I/O) 2.Interrupt Driven I/O (I/O hardware signals CPU) 3. Direct Memory Access Controllers transfer data between main memory and device, bypassing CPU |
| State the method for polling/ programmed I/O running a insturction | Processor executes an I/O instruction by issuing a command to the appropriate I/O controller; Each device is given a unique identifier or address; I/O controller performs the requested action and sets the appropriate bits in I/O status registers; The processor periodically check the status of I/O controller until it finds the operation is completed; One word transfer per I/O instruction. |
| Define polling | The process of periodically checking the status of a I/O device to determine the need to server the device |
| Summarise polling | CPU has direct control over I/O • Sensing status; • Read/write commands; • Transferring data CPU waits for I/O controller to complete operation The simplest way for an IO device to communicatewith processor Wasteful to have processor spend most ofits time “spin-waiting” for I/O to be ready |
| What is interrupt driven | Interrupt the CPU while carrying out its program when the I/O device is ready and return to program when done with data transfer No repeated CPU checking of device |
| What is the read operation for the interrupt driven I/O | • CPU issues a read command to an I/O controller • The I/O controller gets data from a peripheral whilst CPU does other work • I/O controller interrupts CPU • CPU requests data • I/O controller transfers data |
| What are interrupt handlers? | the prgram that services the interrupt nown as the interrupt routine |
| What is context and why is it important in interrupt driven I/O? | It saves registers of the program before control is transferred to the interuppt handlers Important as it allows the porgam to carry on where it left off |
| What happens when there are multiple interrupts? | Each interrupt line has a priority Lower priority interrupt lines have to wait |
| What is the disadvantage of interrupt driven I/O? | Transfer rare is limited The CPU is tied up |
| What is Direct Memory Access? | It transfers large blocks of data to and from memory CPU is not involved in the transfer DMA controller takes over the CPU's role |
| What is a DMA controller? | a specialized controller that transfers data between an I/O device and memory independent of CPU. |
| How does the DMA controller work> | CPU instructs the DMA controller to read/write, device address, starting address of memory block for data and amount of data to be transferred DMA controller deals with transfer adn sends interrupt when finished |
| What ind of device does DMA work best on | High performance devices such as hard disks, graphics card network cards etc |
| What is a magnetic disk? | A computer memory where info is stored by a magnetising material on the surface of a rotating disk Provides nonvoltatile storage |
| Give a two examples of a magnetic disk | Floppy disks (slow, less dense, removable) Hard Disk Drives (faster, more dense, non-removable) , provides long-term cheap storage for files and a backup for main memory |
| What is optical storage? | Optical disc which is portable and is written and read by a laser |
| Name 4 forms of optical storage? | CD-ROM (audio) CD-Recordable DVD (multi-layer, high capacity of 4.7GB, WORM) Blu-ray Disc (dual later, capacity of 50GB) |
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