Input/Output Flashcards
what is a device controller?
electronic circuit capable of operating a device using binary signals
to start an I/O operation, the driver ________
writes the opcode into the opcode register
Prior to starting an I/O operation, the busy flag must be ______
FALSE
When interrupts are used, the driver process is blocked while _______
data is being transferred between the device and controller buffer
a DMA controller is a ___________
hardware device capable of reading and writing to main memory
a DMA transfers data between _______
a device controller and main memory
when is polling more useful than interrupts?
in real time systems where only 1 process is running
The CPU time needed to process an I/O instruction is unpredictable with _____.
polling
The buffer in a device controller decouples _____.
the device from the driver
what is “cooked” input mode?
special characters do not appear in the buffer
what is a disk block cache?
a set of main memory buffers that contain the most recently accessed disk blocks
how are disk block caches organized?
hashing is used
The list of free buffers is not accessed when _____.
a currently resident block is accessed
what is the seek time?
the time to move the r/w head to the track containing the desired data
what is rotational delay?
the time to wait for the desired data item to pass under the r/w head
what is data transfer time?
the time to transfer the desired number of bits to or from the disk
what is peak data transfer rate?
the rate data can be streamed once positioned
what is sustained data rate?
the rate which data can be streamed including seek times and rotational delay
Data on a magnetic disk is accessed in units of _____.
Sectors
The time to seek from one track to another depends on the _____.
number of tracks on the disk
what is shortest seek time first algorithm?
prioritizes data access requests based on the shortest seek time
what is the scan scheduling algorithm?
basically works like an elevator going up and down servicing requests at every track in order. kinda like round robin
what is a parity bit?
a bit added to a string of bits to ensure that the total number of 1’s is even or odd
what is the difference between sector forwarding and sector slipping?
sector forwarding is a remapping…sector slipping is a shift to move away from the bad sector
