Contemporary Architectures

Question 1

Do all components in the computer affect performance?

Answer 1

Yes

Question 2

What are the measurements of the following: CPU, memory and cache and buses?

Answer 2

1. CPU - speed, number of registers
2. Memory & Cache - access time and bandwidth
3. Buses - transfer speed

Question 3

What’s Amdahl’s Law?

Answer 3

Potential speed up of a program using multiple processors compared to a single processor

Question 4

What’s the equation for speedup?

Answer 4

Time to execute program on a single processor / time to execute program on N parallel processors

Question 5

What’s the latency?

Answer 5

Time to solution for 1 instruction (response time)

Question 6

What’s the throughput?

Answer 6

Tasks per unit of time (bandwidth)

Question 7

Give an in-real-life example of latency:

Answer 7

Airplane takes one hour and has 1000 boxes - clock speed

Question 8

Give an in-real-life example of throughput:

Answer 8

Transport shiploads 100,000 boxes - pipelining

Question 9

How do you calculate performance?

Answer 9

1 / CPU time

Question 10

How do you calculate CPU time?

Answer 10

time / cycle, x cycles / instruction, x instructions / task

Question 11

What’s MIPS?

Answer 11

Million Instructions Per Second

Question 12

How do you calculate IPS?

Answer 12

sockets * (cores/socket) * clock * (instructions/cycle)

Question 13

What do IPS measure?

Answer 13

Non-numerical performance

Question 14

What’s a FLOPS?

Answer 14

Floating Point Operations Per Second

Question 15

How do you calculate FLOPS?

Answer 15

sockets * (cores/socket) * (cycles/second) * (FLOPS/cycle)

Question 16

How do you calculate availability in server metrics?

Answer 16

(total elapsed time - a sum of downtime) / total elapsed time

Question 17

How do you calculate reliability in server metrics?

Answer 17

(total elapsed time - a sum of downtime) / number of failures

Question 18

How badly power consumption matters? Explain

Answer 18

Larger and larger databases are taking far more power to run including embedded devices and their battery lives

Question 19

What is the benchmark?

Answer 19

Designed to mimic a particular type of workload on a component or system

Question 20

What are the two types of benchmark?

Answer 20

Synthetic benchmarks responsible for the workload and real-world which give better measurements

Question 21

What’s Goodhart’s Law of 1975?

Answer 21

When a measure becomes a target it ceases to be a good measure

Question 22

What’s quantitative RISC design?

Answer 22

Count frequencies of actual instruction use then reduce instruction set to optimise most common needs

Question 23

Which architecture is the most successful so far?

Answer 23

x86 that is part of CISC family, backward compatibility

Question 24

In 2018, what was the percentage of CPUs that made using RISC?

Answer 24

99%

Question 25

How many bit versions and what are they in RISC?

Answer 25

32, 64 and 128bit versions

Question 26

What are RISC style instructions?

Answer 26

1. Separate memory access from ALU
2. Specify output register
3. Improves pipelines

Question 27

What does X0 - X32 integer registers have?

Answer 27

Standard names for their uses e.g. argument passing

Question 28

What does 32 optional floating-point have?

Answer 28

Registers, control, status registers, stack pointer and no ALU exceptions but you can extend it by having multiplications or division

Question 29

What’s the model of the 1980s operating system?

Answer 29

Everyone has the same CPU, differentiated by computer design very useful for programmers

Question 30

What’s the model of the 1990s - onwards operating system?

Answer 30

Defines the platform, it’s for commercial use

Question 31

What’s CPU privileged mode?

Answer 31

Access to all memory and real addresses and uses stacks to save and restore user program contexts

Question 32

What’s CPU restricted mode?

Answer 32

Only for user programs, it prevents all access

Question 33

What’s an IRQ timer?

Answer 33

Switches to privileged mode than jumps back to the kernel code

Question 34

What’s a UEFI?

Answer 34

Unified Extended Firmware Interface which replaces old BIOS and it executes subroutines

Question 35

Explain what was a meltdown of CPU’s (2018)

Answer 35

One of two exploits discovered on a CPU bug in 2018, people could initially expose the security measures like steal customer’s data, but the vulnerability existed before we knew and to resolve the issue numerous patches were introduced