Samenvatting Basics of computer systems and networks
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Course
Basics of computer systems and networks
Institution
Universiteit Leiden (UL)
Very comprehensive and clear notes on the Basics of computer systems and networks course. This course does not use a book, so you can finish this summary in one go.
Hoorcollege 1 - Basics of Computer Systems and Networks
Multiple choice en deels open vragen – 100% van het cijfer. Alleen vragen over dingen die in tekst in
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Course overview
What happens exactly in your computer, when you type ‘google.com’ in your browser, and you
press Enter?
Normaal – Google komt omhoog en je kunt het gebruiken.
Doel van dit vak – Alle lagen van een computer ontdekken en wat er dus precies gebeurt als
je iets intypt.
Operating systems
Er zijn verschillende systemen, die allemaal net iets anders werken en net ergens anders op gericht
zijn.
Zonder operating system kun je de hardware van je computer niet gebruiken.
What is a computer?
“An electronic device for storing and processing data, typically in binary form, according to
instructions given to it in a variable program.” – Oxford Dictionary
Where do we find computers?
,Organization of modern computer systems
Before understanding eachh component, let’s get familiar with metric.
Question: Computers only understands 0 and 1, why?
Answer: Electricity! If there is current in wire or a unit, it's considered as 1, and if not, it's
considered as 0.
o We are focusing on electrical computers in this course, many of the statements are
not valid for quantum computers.
Computer system metrics
Electricity current = 1
Electricity current = 0
In terms of computer science:
o 1 is equal to true/ on.
o 0 is equal to false/ off.
Bit: a unit of data that can be 0 (false) or 1 (true).
Byte: A pack of 8 bits is a byte.
o Why 8 bits in 1 byte?
o Why 6 bits is not 1 byte?
o Why 10 bits is not 1 byte?
In ancient times, 6 bits was 1 byte.
But that was too small, so they decided to use 8.
Also 8 is a power of 2 8 = 2^3
In computer hardware, it’s usually better for hardware to have metrics in powers of 3.
The reason is that every bite van have the state of 1 or 0 and it’s actually like having numbers
in base 2 format. To maximize a number in base 2, it would be better to have the hardware
bits in power of 2.
,Kb versus KB
Lowercase b = Bit
o Kb = Kilo Bit
o 1Kb = 1000 Bits
Uppercase B = Byte
o KB = Kilo Byte
o 1KB = 1000 Bytes
8 Kb = 1KB
Bigger bit/ byte metrics
Some examples of storage required for different files
Phone camera photo stored as JPEG: ~5 MB
3 minute song in MP3 format: ~5MB
Word document with 40 pages of text: ~5MB
PDF file of a bachelor thesis: ~9MB
Phone software update: ~500 MB
A 2 hour movie full HD: ~ 2GB
Call Of Duty: Modern Warfare: ~235GB
CERN Large Hadron Collider data: ~280 PB
Adding time
Adding time metric to KB will result in KBps
KBps = Kilo Byte per second
MBps = Mega Byte per second
o If you have an internet connection with the speed of 100MBps, you can download
100MB file in 1 second.
, However, internet providers usually like to advertise the network speed with Mbps instead of MBps.
So if you have a 100 Mbps internet connection, your download speed will be:
= 12,5 MBps
And downloading a 100 MB file will take 8 seconds.
CPU (Central Processing Unit)
The brain of the computer.
Is extremely fast in processing data.
Accept bits, processes them, and the outputs are also bits.
Advantage: Super fast.
Disadvantage: Storage limitation.
Main memory – Random Access Memory (RAM)
CPU is good at processing, but it has a very limited storage capacity. Ram on the other hand,
is a temporary storage solution to aid CPU for storing data.
RAM is typically referred to as the computer’s working memory.
Advantage: Super fast.
Disadvantage: Expensive, not permanent.
How does the CPU communicates with RAM?
BUS is an electronic device for storing and processing data, typically in binary form, according to
instructions given to it in variable program.
How to store data permanently?
Storage device (HDD, SDD).
Data is stored even when the computer is not powered on.
Why don’t we simply replace RAM by storage devices?
Basically because of speed and cost.
o But even with newer SSDs, there are still issues.
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