Exam 1

Question 1

Code Motion

Answer 1

Code motion is when you reduce the frequency that a computation is performed. Especially moving code out of loop

Question 2

Strength Reduction

Answer 2

Reduction in strength is when you replace a costly operation with a simpler one. Ie, replacing multiplication with addition.

Question 3

In-Lining

Answer 3

In-lining is an optimization technique that may be used to improve performance when a small function is called from within a high iteration loop

Question 4

Loop-unrolling

Answer 4

Loop unrolling is when you move code outside of a loop and expand it to minimize the number of instructions that are executed; the performance improvement comes from the fact that fewer instrs are being executed

Question 5

Superscalar architecture

Answer 5

Can issue and execute multiple instructions in one cycle; they’re retrieved from a sequential instruction stream and are usually scheduled dynamically. Can take advantage of instruction level parallelism

Question 6

Speculative execution

Answer 6

Speculative execution is an optimization where the system performs a task way ahead of time, that may or may not be needed, in order to prevent a delay from occurring when and if the work is actually needed.

Question 7

RAS and CAS

Answer 7

Row Address Strobe

Column Address Strobe

Question 8

Platters

Answer 8

Construct the disk; consist of two sides called surfaces

Question 9

Surfaces

Answer 9

Make up platters and are coated with magnetic recording material

Question 10

Cylinders

Answer 10

The collection of tracks on all the surfaces that are equidistant from the center of the spindle

Question 11

Rotational rate

Answer 11

Measured in RPM; how fast the spindle spins on the platter

Question 12

Track

Answer 12

Located on surfaces in concentric rings

Question 13

Sector

Answer 13

How each individual track is partitioned

Question 14

Recording density

Answer 14

(bits/in) The number of bits that can be squeezed into a 1 inch segment of the track

Question 15

Track density

Answer 15

(tracks/in) The number of tracks that can be sequeezed into a 1-inch segment of the radius extending from the center of the platter

Question 16

Areal density

Answer 16

The product of the recording density and the track density

Question 17

Disk capacity

Answer 17

bytes/sector * average # sectors/track * # tracks/surface * #surfaces/platter * # platters/disk

Question 18

Seek time

Answer 18

The time required to move the arm over the track that contains the target sector

Question 19

Rotational latency

Answer 19

Once the head is in position over the track, the amount of time it takes for the first bit of the target sector to pass under the head

Question 20

Transfer time

Answer 20

1/RPM * 1/average # sector/track * 60 secs/1 min

Question 21

Cache Block

Answer 21

The data in the cache

Question 22

Cache line

Answer 22

cache size/block size

Question 23

Cach Sets

Answer 23

number of lines/lines per set

Question 24

Cache associativity

Answer 24

of lines per set

Question 25

Direct-mapped cache

Answer 25

Each main memory address maps to exactly one cache block Advantages: Simple technique and the mapping scheme is easy to implement. Disadvantages: Each block of main memory maps to a fixed location in the cache; therefore, if two different blocks map to the same location in cache and they are continually referenced, the two blocks will be continually swapped in and out (known as thrashing)

Question 26

Fully associative cache

Answer 26

Permits data to be stored in any cache block, instead of forcing each memory address into one particular block. Advantages: Much better hit rate Disadvantages: Slower access time

Question 27

Write-through

Answer 27

Write immediately to memory

Question 28

Write-allocate

Answer 28

Load into cache, update line in cache

Question 29

Write-back

Answer 29

Defer write to memory until replacement of line; need a dirty bit

Question 30

No-write-allocate

Answer 30

Writes straight to memory, does not load into cache

Question 31

What happens when you increase cache size?

Answer 31

Decrease miss rate, increase hit time

Question 32

What happens when you increase block size?

Answer 32

decrease miss rate, increase miss penalty

Question 33

What happens when you increase associativity?

Answer 33

decrease miss rate, increase hit time, increase miss penalty

Question 34

Trap

Answer 34

The type of exception that occurs intentionally as a result of executing an instruction. Example: User program opens a file

Question 35

Interrupts

Answer 35

The type of exception that is generated by an I/O device. Example: I/O device completes request

Question 36

Fault

Answer 36

If a process causes an access to data or instruction that is not currently in main memory. Example: Read of a instruction not currently in main memory

Question 37

Abort

Answer 37

If a process causes an access to corrupted data or instructions. Example: Hardware error

Question 38

Concurrent processing

Answer 38

Single processor executes multiple processes concurrently. Register values for nonexecuting process saved in memory

Question 39

Logical control flow

Answer 39

Each program seems to have exclusive use of the CPU, provided by kernel mechanism called context switching.

Question 40

Private virtual address space

Answer 40

Each program seems to have exclusive use of main memory. Provided by kernel mechanism called virtual memory

Question 41

Context switch

Answer 41

Processes are managed by a shared chunk of memory resident OS code called the kernel. Important: the kernel is not a separate process, but rather runs as part of some existing process. Control flow passes from one process to another via a context switch

Question 42

errno

Answer 42

On error, Linux system-level functions typically return -1 and set global variable errno to indicate cause.

Question 43

exit()

Answer 43

Terminates with an exit status of status. Convention: normal return status is 0, nonzero on error. Another way to explicitly set the exit status is to return an integer value from the main routine

Question 44

zombie

Answer 44

When process terminates, it still consumes system resources. Examples: Exit status, various OS tables. Called a “zombie”. Living corpse, half alive and half dead

Question 45

Rotation time

Answer 45

1/RPM * 60 secs/1 minute

Question 46

Seek time

Answer 46

60 seconds/RPM