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Computer Science > Hardware > Flashcards

Hardware Flashcards

1
Q

What are embedded systems?

A

An embedded system is a computer system built within a larger device.

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2
Q

Three examples of an embedded system

A

Washing machine, digital camera and GPS systems

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3
Q

What is the task of the embedded system?

A

It includes both hardware and software and its purpose is to control the device and to allow a user to interact with it. They tend to have one, or a limited number of tasks that they can perform.

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4
Q

What are the advantages of embedded systems?

A

Their limited number of functions means they are cheaper to design and build.
They tend to require less power. Some devices run from batteries.
They do not need much processing power. They can be built using cheaper, less powerful processors.

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5
Q

What is the Von Neumann architecture?

A

data and instructions are both stored as binary digits

data and instructions are both stored in primary memory

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6
Q

What are the 6 main CPU components?

A

The central processing unit (CPU) consists of six main components:

control unit (CU)
arithmetic logic unit (ALU)
registers
cache
buses
clock
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7
Q

What are the 3 functions of the control unit?

A

The CU provides several functions:

it fetches, decodes and executes instructions
it issues control signals that control hardware
it moves data around the system

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8
Q

What are the 2 main functions of the Arithmetic Logic Unit?

A

The ALU has two main functions:

It performs arithmetic and logical operations (decisions). The ALU is where calculations are done and where decisions are made.
It acts as a gateway between primary memory and secondary storage . Data transferred between them passes through the ALU.

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9
Q

What are registers?

A

Registers are small amounts of high-speed memory contained within the CPU.

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10
Q

What does the program counter do?

A

program counter - holds the memory address of the next instruction to be fetched from primary memory

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11
Q

What does the memory address register do?

A

memory address register (MAR) - holds the address of the current instruction that is to be fetched from memory, or the address in memory to which data is to be transferred

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12
Q

What does the memory data register do?

A

memory data register (MDR) - holds the contents found at the address held in the MAR, or data which is to be transferred to primary memory

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13
Q

What does the Accumulator do?

A

accumulator (ACC) – holds the data being processed and the results of processing

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14
Q

What does the current instruction register do?

A

current instruction register (CIR) - holds the instruction that is currently being decoded and executed

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15
Q

What is cache?

A

Cache is a small amount of high-speed random access memory (RAM) built directly within the processor. It is used to temporarily hold data and instructions that the processor is likely to reuse.

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16
Q

What is the clock?

A

The CPU contains a clock which is used to coordinate all of the computer’s components. The clock sends out a regular electrical pulse which synchronises (keeps in time) all the components.

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17
Q

What is clock speed?

A

The frequency of the pulses is known as the clock speed. Clock speed is measured in hertz. The higher the frequency, the more instructions can be performed in any given moment of time.

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18
Q

What is a bus?

A

A bus is a high-speed internal connection. Buses are used to send control signals and data between the processor and other components.

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19
Q

What are the three buses?

A

Three types of bus are used:

Address bus - carries memory addresses from the processor to other components such as primary memory and input/output devices.
Data bus - carries the actual data between the processor and other components.
Control bus - carries control signals from the processor to other components. The control bus also carries the clock’s pulses.

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20
Q

What is the fetch decode and execute cycle?

A

In the fetch part of the cycle, instructions and data are moved from the random access memory to the central processing unit. In the execute part of the cycle, the control unit decodes or interprets the instructions and decides what action to perform. These instructions are then carried out.

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21
Q

Factors that affect CPU’s peformance

A

clock speed
cache size
number of cores

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22
Q

How does Clock speed effect the CPU’s performance?

A

The higher the clock speed, the greater the number of instructions and some can be overclocked to make them run at higher clock speed than the factory set rate = lead to overheating + shortening of life + crashing or permanent damage to the system. You need a high performance cooling system are needed

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23
Q

How does the number of cores affect CPU performance?

A

Each core can process data independently of the rest so more instructions can be carried at once the more cores with PCs and smartphones having 4+ // software needs to be designed to use multicore processing so not all processing tasks are split equally leading to one core waiting for other cores

24
Q

How does the size of cache affect the performance of CPU?

A

A larger cache gives the CPU faster access to more data it needs to process so will able to perform better

25
Q

What is a multi-core processor?

A

A multi-core processor has more than one CPU.

26
Q

What are the advantages of using multi-core processors?

A

The advantages of multiple core processors over single core processors are:
* the cores can work together on the same program; this is called parallel
processing
* the cores can work on different programs at the same time; this is called multi tasking

27
Q

What is secondary storage?

A

Secondary storage is non-volatile, long-term storage.

28
Q

What is primary storage?

A

The primary memory such as random access memory (RAM) and cache is used to hold data that is being processed. (Volatile)

29
Q

Why is primary storage needed?

A

Primary storage devices have a direct connection to the CPU core and some of them are built into the CPU chip itself.
Primary storage devices are extremely fast and so the CPU can run at top speed. Trying to run a program directly from secondary storage such as a hard disk would not allow the CPU to run at anywhere near of what it is capable of.

30
Q

What are some examples of main memory?

A

Random Access Memory (RAM)
ROM chips
Cache
CPU registers

31
Q

What is RAM?

A

RAM is used as main memory. It acts as a temporary store for program instructions and data. It can only store things temporarily because it is volatile - it must constantly be powered or it will lose any data it is holding.
It is useful as a temporary store because any data or instructions in RAM can be accessed in any order, i.e. it can be accessed non sequentially. This is why it is called Random Access Memory.
Because the CPU can access any memory location at any time, programs held in RAM can run very quickly.

32
Q

What is ROM?

A

Read Only Memory (ROM) is a type of primary storage because it is directly accessed by the CPU. Just like RAM, memory locations in ROM can be accessed in any order.

33
Q

What is the difference between ROM and RAM?

A

ROM is Read Only Memory which means that its data content cannot be changed, overwritten or removed by a running program, whereas RAM is read/write memory which means that the contents can be altered.
Secondly, unlike RAM, ROM is non volatile, meaning it keeps its data when there is no power supply.
Thirdly, ROM may be just a few megabytes but usually GBs of RAM
Next, ROM is used to hold basic computer hardware settings and in the past it held the BIOS to boot up the computer while RAM is used as main memory to hold both data and programs
Lastly, ROM chips are usually located on the motherboard or printed circuit board such as a graphics card. They are not removable as they are soldered into the motherboard whereas RAM chips are located in removable memory modules that are slotted into sockets on the motherboard. This means they can be easily removed and updated.

34
Q

What does the ROM hold?

A

It contains the instructions called BIOS (Basic Input Output System) a computer needs to properly boot up. As soon as the computer is powered on the CPU read the instructions from ROM and tells the CPU to perform self checks+ set up the computer + see what hardware is present and copy the operating system into RAM

35
Q

When is Virtual memory needed?

A

When RAM gets too full, the computer operating system can help out by temporarily marking sections of secondary storage for the CPU to store data on. These sections are called virtual memory.

36
Q

What does Virtual Memory do?

A

Let’s say the CPU needs to use a block of data but it is sitting in virtual memory. First of all the operating system works out which data is the least-used in RAM at that instant. It then stores that chunk of data in virtual memory located on the hard disk and clears it from RAM. This gives enough room to re-load the needed data from virtual memory. This moving back-and-forth between RAM and virtual memory continues as long as there isn’t enough RAM to store all the data needed by the set of running applications.

37
Q

Is virtual memory volatile and why?

A

Virtual memory is effectively volatile even though the data is stored on hard disk. If the computer is turned off, the operating system loses track of the content of virtual memory and so starts with a clean slate once more. Even though the CPU can use virtual memory - it is very slow compared to RAM.

38
Q

How does Virtual memory affect performance?

A

Even though the CPU can use virtual memory - it is very slow compared to RAM. This is because the transfer rates between secondary storage is much slower than RAM slowing the whole process down

39
Q

What is a problem that occurs when virtual memory is being used too heavily?

A

Disk Thrashing is a problem that may occur when virtual memory is being used too heavily. As main memory fills up, then more and more pages need to be swapped in and out of virtual memory. This swapping leads to a very high rate of hard disk access leading to wear and tear on the disk and a slow-down in overall performance.

40
Q

What is the solution to disk thrashing?

A

The solution is to either fit more RAM or reduce the amount of applications being used at the same time.

41
Q

What are the three main types of secondary storage?

A

Secondary storage devices are generally separated into three types:

magnetic storage devices, such as hard disk drives
optical storage devices, such as CD, DVD and Blu-ray discs
solid state storage devices, such as solid state drives and USB memory sticks

42
Q

How does a magnetic storage devices work?

A

Magnetic devices such as hard disk drives use magnetic fields to magnetise tiny individual sections of a metal spinning disk. Each tiny section represents one bit. A magnetised section represents a binary ‘1’ and a demagnetised section represents a binary ‘0’. These sections are so tiny that disks can contain terabytes (TB) of data.

As the disk is spinning, a read/write head moves across its surface. To write data, the head magnetises or demagnetises a section of the disk that is spinning under it. To read data, the head makes a note of whether the section is magnetised or not.

43
Q

What are the pros of magnetic devices?

A

-Huge capacity, offers up to several terabytes per device.
-Low cost per gigabyte - magnetic tape is the cheapest, but hard disk is very low as well.
-Hard Disk offers high speed data access
-Hard Disk offers random access to data
-Magnetic tape can hold its data for up to thirty years in the correct environment.

44
Q

What are the cons of magnetic devices?

A

-Not as portable as other technologies. But external hard disks are commonly available, but they need to be treated carefully.
-Hard disk has mechanical moving parts, so less rugged than solid state storage.
-Data can be lost near strong magnetic fields, such as being too near an audio speaker.
-Magnetic tape uses serial data access and so is very slow.
-Data read \ write is not as fast as flash technology

45
Q

How do optical devices work?

A

Optical devices use a laser to scan the surface of a spinning disc made from metal and plastic. The disc surface is divided into tracks, with each track containing many flat areas and hollows. The flat areas are known as lands and the hollows as pits.

When the laser shines on the disc surface, lands reflect the light back, whereas pits scatter the laser beam. A sensor looks for the reflected light. Reflected light (lands) represents a binary ‘1’, and no reflection (pits) represents a binary ‘0’.

46
Q

What are the three types of optical storage and an explanation of each?

A

ROMmedia have data pre-written on them. The data cannot be overwritten. Music, films, software and games are often distributed this way.
R media are blank. An optical device writes data to them by shining a laser onto the disc. The laser burns pits to represent ‘0’s. The media can only be written to once, but read many times. Copies of data are often made using these media.
RW works in a similar way to R, except that the disc can be written to more than once.

47
Q

What are the pros of optical storage?

A

-Cheap if less than 10GB needs to be stored per media item.
- Very portable compared to hard disk
- Ideally sized (5 - 50GB) for storing movies and videos. Which is why they were created in the first place.
- Immune to magnetic fields.

48
Q

What are the cons of optical storage?

A

-Not cheap if terabytes need to be stored
-Not as portable as Flash media
-Slow to write (burn) to and much slower than hard disk to access.
-Easily scratched
-Cannot write over stored data (Sometimes)

49
Q

What is solid state storage?

A

Solid state devices use non-volatile random access memory (RAM) to store data indefinitely.

50
Q

What are the pros of solid state storage?

A
  • Faster than hard disk as no mechanical parts need to be moved to read / write data.
  • Large capacity, especially in the form of a solid state drive.
  • Solid State Drives are silent unlike hard disks
  • No moving parts there is less chance of losing data
  • Very portable in the form of SD memory cards and USB memory sticks.
51
Q

What are the cons of solid state storage?

A
  • Less durable than a hard disk as it has a limited number of erase \ write cycles - maybe a 100,000 cycles before it wears out.
  • Solid State Drives are expensive compared to a hard disk of similar capacity.
  • The storage capacity is less than a HDD
52
Q

What to consider before buying an storage device?

A

Cost - what is the cost per gigabyte (GB)?
Capacity - how much data can the medium hold?
Speed of access - how quickly can data be transferred to and from the medium?
Portability - how portable is the medium? Does it need to be portable?
Durability - how robust is the medium, and how robust will it need to be?
Reliability - how resilient and long-lasting is the medium?

SPCCDR

53
Q

What is a problem that occurs when virtual memory is being used too heavily?

A

Disk Thrashing is a problem that may occur when virtual memory is being used too heavily. As main memory fills up, then more and more pages need to be swapped in and out of virtual memory. This swapping leads to a very high rate of hard disk access leading to wear and tear on the disk and a slow-down in overall performance.

54
Q

What is the typical storage for optical devices?

A

Compact Disk (CD) = 700MB
Single layer DVD = 4.7GB
Double layer DVD = 8.5GB
Blue-rays = 25GB

55
Q

What is the typical storage for flash devices?

A

SD memory cards = to 64 GB and more
USB Memory stick = to 64 GB and more
Solid State Drives (SSD) = 300GB - 1TB

56
Q

What is typical storage for Magnetic storage devices?

A

Hard Disk = 300GB - 6TB
Magnetic Tape = to 185 TB and more // typically used for data archiving

Computer Science (9 decks)

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