Unit 3 Computer Architecture & Storage Flashcards
What does the CPU do?
The CPU processes instructions
When you run a program, it is the
CPU which processes the
instructions and data that are input
The results are then output
What are the 2 major components of the CPU?
Arithmetic logic unit(ALU) and Control unit (CU)
What is a register?
A register is a very fast
memory location in the
CPU itself
Name all CPU registers and state their purpose.
Program Counter (PC)
holds the address of the next instruction to be executed
Memory Address Register (MAR)
Holds the memory address of where data or instructions are to be fetched
Memory Data Register (MDR)
Stores the data or instruction which has been fetched from memory
Current Instruction Register (CIR)
holds the instruction currently being executed or decoded
Accumulator (ACC)
holds the result of an instruction before it is transferred
to memory
What is the purpose of the control unit?
The control unit coordinates and controls
all of the activities taking place within
the CPU
It decodes instructions and executes them
It receives signals from the system clock
What does the ALU do?
The ALU or Arithmetic Logic Unit is where the actual
arithmetic operations are done
It also carries out logical operations such as those including
AND, OR and NOT
How does the fetch-decode-execute cycle work?
The CPU operates by repeating
three operations:
FETCH – causes the next
instruction and any data
involved to be fetched from
main memory
DECODE – decodes the
instruction
EXECUTE – the instruction
is executed
This process is then repeated…
What does the program counter do?
The Program Counter holds
the address of the next
instruction to be executed
What does the accumulator do?
Accumulator
The accumulator (ACC) is
where arithmetic and logic
results are temporarily stored,
much like the M+ function on
a calculator
What do the MAR and MDR do?
The MAR holds the memory address of where instructions are to be fetched from memory
The MDR holds the actual instruction, and the data that has been fetched.
What does the CIR do?
The current instruction register holds the instruction that is being executed or decoded at the moment
What affects CPU performance?
Clock speed
Processor cores
Cache
What is clock speed?
Everything in a computer happens on the pulse of
the internal clock
Therefore, the faster the clock speed, the faster the
instructions are processed
How do multi-core processors work?
A dual-core processor has two processors in the
same integrated circuit, linked together
A dual-core processor has the potential to perform two
instructions at the same time
This allows twice as many instructions to be executed,
however, it doesn’t always perform at this rate as software
may not be able to take full advantage of both cores
WHy can multi core be faster than single core?
A quad-core processor working on many different
tasks simultaneously, under ideal conditions can be
up to four times faster than a single-core processor
How does cache memory work?
Cache is a small amount of very
fast, expensive memory in the CPU
It can be accessed faster than
regular main memory (RAM)
What are the levels of cache mamory?
Level 1 cache is extremely fast but small (between 2-256KB),
located on the CPU. Each core will have its own
Level 1 cache
Level 2 cache is usually also given to each core. It is very
fast, but a little slower than Level 1 cache. The typical size is
256KB-8MB
Level 3 cache is the slowest type of cache, but still faster
than RAM. It is usually located on the CPU and stores
4MB-50MB. The cache is shared between all the cores on
the processor
What are the benefits of cache?
The data used most often by the CPU is held in
Level 1 cache so is available extremely quickly
In most systems, Level 1 cache is used about 50% of the time,
with Level 2 cache being accessed about 90% of the time
This greatly reduces the time that the CPU has to wait for data
from main memory
The size of the Level 2 cache is a major factor in
determining the performance of the CPU
What are buses?
A bus is a set of parallel wires connecting two or
more components of the computer
What are the 3 buses that make up the system bus?
Address Bus: stores the address of the memory or device
controller to be read from or written to
Data Bus: carries data throughout the computer system
Control Bus: uses control signals to control all activities
within the CPU
What are external buses?
The CPU is also
connected to the external
Input-output device
controllers by means of
the system bus
What are instruction sets?
Instruction sets are all the possible instructions that
are able to be decoded and executed by a CPU
What are operands and operators?
An operator performs an operation (calculation) on the
operand(s)
The operands are the values used
What are opcodes and operands?
When programming a processor a special language
called assembly code is used
The program is then assembled into a binary form known as
machine code – this is what is run by the processor
The assembly code (and machine code) make use of
opcodes and operands
The opcode is the instruction and the operands are the values
that the instruction works on
What is a microprocessor?
A microprocessor is an integrated circuit that is all
contained on a single chip
CPUs are one type of microprocessor, they include Pentium
microprocessors and ARM microprocessors
Microcontrollers contain not only the
microprocessor, but also RAM and
ROM or flash memory for volatile and
non-volatile storage – this allows
for an entire computer to
be contained on one chip
What is an embedded system?
An embedded computer is a single microprocessor
that includes RAM, ROM and a CPU
What embedded systems do cars use?
Some examples of embedded systems in
cars include:
Cruise control
Engine cooling fan
Interior fans and temperature
Interior lighting
Rear cameras and remote parking
Infotainment systems (entertainment / information / satnav)
Engine control unit (ECU)
What is the cloud?
The cloud is another name for services
offered via the Internet
The name comes from network diagrams
that use a cloud symbol to represent
the Internet
The cloud can be split into two
major areas:
Cloud storage
Cloud computing
What is cloud storage?
Cloud storage allows users to
store files and data on
the Internet
The files are accessed remotely
by users
Data may be stored in
multiple locations
What are some cloud storage features?
Further features include:
Synchronisation of devices
with the cloud storage
24/7 Availability
Redundancy
Multiple file versions
Only pay for storage used
Scalability
What is redundancy?
Storage redundancy is where multiple copies of files
are stored in different locations
In local storage this is normally carried out by having multiple
copies of files on two different hard drives in one server
In cloud storage the locations that store redundant files may
be anywhere in the world
What is scalability?
Scalability is the ability of the storage system or
cloud computing resources to increase in size
A home PC doesn’t have scalable storage. It may be possible
to have two or three hard disks, but not two or three hundred
Cloud storage normally charges for the amount of
storage used
Increasing offline storage usually requires
the purchase of new disks
What are data centres?
Data centres are buildings that
are dedicated to storing
physical servers
Each server will contain an array
of hard drives
Professional engineers will manage
the computers
The buildings will have temperature
control and air conditioning
Uptimes for data centres are often
better than 99.99%
Explain data transfer speeds
When a file is used that is on cloud storage it must
first be downloaded
With a fast connection and a small office document this may
happen in a few seconds
However, with files such as those used in video editing it may
take hours to open or save files to cloud storage
Local storage is very fast to transfer data
A local SATA solid state drive can read and write data at
around 500 MB per second
A typical UK internet connection operates at around 70 Mb/s
giving speeds of less than 10 MB per second
What are the types of memory used in computers?
RAM
CPU Registers
ROM
Cache
Virtual memory
What are the types of primary storage?
There are many types of memory used in computers
In the Von Neumann architecture, primary storage is directly
accessed by the CPU and is needed to store programs that
are currently running
The two types used as primary storage are:
RAM (Random Access Memory)
ROM (Read Only Memory)
How does RAM work?
RAM stores programs or data that are running
or open
It is directly accessed by the CPU
When your computer is turned off, data stored in RAM is lost
RAM is volatile as it loses data if the power is off
All your programs and data are stored permanently
on your hard drive
When you turn your PC on, what data is stored on the RAM?
None, it is volatile memory.
Explain programs and data in terms of RAM
When applications or programs are
loaded, they are copied into RAM from
the hard drive
Documents and files (data) that are used with
those programs are also opened by copying
them into RAM
RAM starts to fill up as all these
programs, documents and files are copied
What is virtual memory?
Virtual memory is part of the
hard drive used as an extension
to RAM
A page of data is a fixed-length
block of virtual memory
When pages of data are moved
between RAM and hard disk this is
known as swapping or paging
Name adv and disadv of virtual memory
Uses cheap secondary storage on the hard drive
Prevents error messages saying ‘out of memory’ – the
programs and files will still open
Disadvantages
Accessing virtual memory is very slow
To access data, the existing data in RAM needs to be copied
to the virtual memory, then data in virtual memory needs to be
copied to RAM
What is ROM?
Some data needs to be permanently held in primary
storage, even when a computer has no power
Read-only memory (ROM) is used to store this data
Data is read from ROM, but cannot be written to it
It is non-volatile as the data isn’t lost if the power is off
What does ROM store?
ROM is used in modern computers to store:
The initial program that is run when the computer is turned on
This is known as the bootstrap
It tells the computer where it will find the operating system on
the hard drive
It also stores the Basic Input/Output System (BIOS)
The BIOS can run without a hard drive or other secondary
storage being present
It controls basic technical configuration of the computer such
as the processor speed and system time
Ram vs rom differences
Ram typically 8-32GB ROM typically 4-8mb
RAM stores running programs and OS while ROM stores bootrstrap and BIOS.
RAM and ROM both have read ability.
ROM does not have the write ability.
ROM is non volatile.
What is secondary storage used for?
It has many different uses – for example:
Programs and data are stored on hard drive
Blu-rays may be used to distribute films
Memory sticks may be used to transport data from one place
to another
Magnetic tape or external hard drives may be used for backup
SD cards can be used for additional storage on cameras
and smartphones – this is used for music, video and photos
Name 2 types of secondary storage
SSD, HDD
Types of storage methods
Magnetic: Mechanical parts move over the disks
surface to read and write data magnetically, or a
drive head reads a magnetic tape
Optical: Lasers read and write data using light
Solid State: Data is recorded onto solid memory
chips without any moving parts
What are magnetic disks?
Basic features:
Disk contains concentric
circles called tracks
Each track is divided
into sectors
Disk heads mounted on
mechanical arms read
and write the data
Advantages and disadvantages of magnetic storage
Advantages:
Cheap, large storage capacities, relatively fast write speed
Disadvantages:
Lots of mechanical parts, durability an issue, sealed unit due
to disk head and platter precision and not very portable
Uses:
Personal computers, storage of large quantities of data
Capacity:
500GB - 12TB or greater
What is optical sotrage?
Basic features:
Data is stored as pits and
lands burnt or pressed into a
spiral track circulating
outwards from the centre
A laser beam passes over the
pits and lands the level of
reflection is measured
From this signal, 0s and 1s
can be derived
Optical storage adv and disadv
Advantages:
Cheap, very easily portable, takes up little space physically
Disadvantages:
Less storage capacity compared to other types
Easily damaged / scratched, requires a CD reader
Slow write speeds
Uses:
Songs, videos and other multi-media storage, backup and
archiving of data
Capacity:
CD-ROM – up to 720 MB
DVD – up to 8.4 GB (dual layered disk)
Blu-Ray – up to 50 GB (dual layered disk)
What is SSD?
Basic features:
Solid-state disks use
non-volatile flash memory to
store information
Very fast read/write speeds as
it doesn’t need to wait for a
disk to spin to the correct
location and an arm to move
No mechanical or moving
parts meaning these disks are
very durable
Adv and disadv of SSD
Advantages:
Highly durable, no moving parts, very fast read/write speeds,
no noisy fan or drive arm, faster start up times
Disadvantages:
More expensive than magnetic hard disks, similar storage
capacity as magnetic disks
Uses:
Higher end computers
Laptops
Smartphones and tablets
Capacity:
100GB – 16TB
What are the two types of flash memory?
NOR flash memory is used for programs
Reading from NOR flash is random access like RAM
It is used to store code such as the BIOS and possibly an
operating system and code is executed directly by the CPU
NAND memory is used for data storage
NAND memory works like other secondary storage
Data is first copied to RAM before it is accessed by the CPU
How does flash memory store data?
A floating gate may store or not store electrons
If no electrons are present in the floating gate the current will
flow, representing a 1
If electrons are stored in the floating gate, the current doesn’t
flow, representing a 0
What is the isolation layer in flash memory?
The isolation layers are semiconductors known
as transistors
In order to write to the flash memory cell, the electrons need
to pass through the isolation layer
The electrons only move through this layer when writing
Normally, they remain trapped in the floating gate
How does flash memory write data?
The control gate is used to move electrons into or
out of the floating gate
A negative voltage forces electrons out of the floating gate
A positive voltage forces electrons into the floating gate
