Computer Hardware

RECALL: The Von Neumann Architecture

John von Neumann created a simplified computing model
- No separate memory for data and for instructions (harvard arch.)
- No ability to apply the same instruction to multiple data (GPUs)

Compromised of a CPU, memory, and input.output devices, possibly (secondary) storage

1. CPU
2. RAM
3. SDRAM
4. ROM
5. BIOS
6. PCI

1.CPU = Central Processing Unit
2. RAM = Random Access memory
3. SDRAM = Synchronous Dynamic RAM
- DDR, DDR2, DDR3, DDR4 - Double Data Rate SDRAM
4. ROM = Read Only Memory
5. BIOS = Basic Input Output System
6. PCI = Peripheral Component Interconnect
- Obsolete, replaced with PCI Express (PCIe)

Data Flow

Central Processing Unit - (CPU):

Decodes instructions and carries out the corresponding arithmetic, logic, or control operations

Sometimes replaceable (in desktops), often permanently soldered to motherboard

Processing speed

Computation occurs in “cycles”, some CPU instructions require more than one cycle

Base unit: Hz - measured cycles per second
- Recall: Hz is also used in sampling frequencies

Storage space

Data is represented in “bits”
Base unit: Byte = 8 bits

Is Measuring in base units impractical? if so what is done instead?

Measuring in base units are impractical in contemporary computing, so they are combined with metric (or binary) prefixes to represent larger magnitudes

Examples: gigahertz (GHz) or terabytes (TB)

CPU and Other Components

Outside the CPU:
Main memory
Data Bus
Control Bus

Inside the CPU:
Cache memory
ALU - Algorithmic Logic Unit
Control Unit
Registers

Note: Speed of a computer is referred to as a ‘clock speed’

Control unit (CU)

Coordinates the flow of instructions and data between the other components of the CPU, activates appropriate components

In other words, control unit carries out control functions
-Retrieving, writing and controlling other peripherals
*does not to calculations

Arithmetic logic unit (ALU)

Performs arithmetic, logical, and bit manipulation operations

Where instructions are applied to data

Registers

Stores values, such as the operands of the currently executing instruction, and results of operations, and memory addresses to across, e.g.,

Registers (ACC)

Accumulator

Stores data results from operations

Registers (PC)

Program Counter

Addresses are stored here

Registers (IR)

Instruction Register

Executed address (at the time) is stored here

Main Memory

Also known as dynamic random access memory (DRAM or just RAM)

A collection of temporary storage locations, each with a unique physical address

Used to store instructions and data for currently running programs

Could be an instruction, a natural number, a signed integer, a character, part of an image

Volatile Memory:

Erased once powered off

CPU + Memory:

The Fetch-Decode-Execute Cycle

Processing Speed:
- Computation occurs in cycles, some CPU instructions require more than one clock cycle to execute. However, fetching the next from RAM can take even longer!

CPU: Multiple Processing Cores

CPUs contain multiple cores, each with their own set of CU, registers, and ALU

Each core can run a separate thread of program execution

CPU: Other Features (Cache Memory)

Temporary storage for recently accessed data; faster to access than main memory (remember fetching?)

Has its own memory for quick access to data

CPU: Other Features (Turbo Boost)

Increasing the processing speed of one or more cores; typically requires disabling other cores to ensure continued stable operation

In other words, increases clock speed

CPU: Other Features (Hyper-threading)

Processing two unrelated instructions simultaneously in the same core; yields better performance than one ordinary core, but not as much as two real cores (due to overhead requirement of unrelated instructions)

- (Simply put): Each core can run a separate thread of program execution

Graphics Processing Unit (GPU)

A processor specialising in rendering 3D graphics

These operations do not require sophisticated computing cores, so 100s - 1000s of cores can exist in a single GPU
- Much faster than CPUs

Buses

Like a data highway that connects computer components

CPU-RAM bus

PCI-express bus connects CPU to other components
-Bus width varies from “x1” (1 bit, 1 “lane”) to “x32”
(32 bits)
- X32 version is rate, x16 is typically the
fastest available

Hard disk drive (HDD):

Mechanical in nature

Contains one or more spinning magnetic disks (platters)

Fixed storage (media cannot be separated from the drive)

Blue-Ray, DVD and CD:

Optical in nature ‘lasers are used to read the disks
Removable storage

Solid State versus Hard Disk Drives

SSDs: (SSD means no moving parts)

Resistant to physical shock
Lower data access time / Higher data transfer rates
More expensive
Capacities up to about 100 TB
Advantage: Limited (though high) number of writes

HDDs:

Sensitive to physical shock
Higher data access time / Lower data transfer rates
Less expensive
Capacities up to about 20 TB

Flash-Based Storage (fast)

Uses solid state memory chips

Non-volatile, so they retain state without a power source

Cells can only endure a limited number of writes

Different types of flash memory technology
Single level cell (SLC)
Multi level cell (MLC)
Three level cell (TLC)
Quad level cell (QLC)

Techniques for extending lifespan of cells:

Provisioning: include extra capacity to use when cells start to fail
Wear levelling: distribute writes so that all cells wear evenly

USB “thumb” drive, flash cards

removable , portable storage
Basic performance for occasionally reading/writing a few files

Solid state storage drive (SSD):

Fixed, internal storage
Improved performance for constantly reading/writing random files, performing error checking, and securing data

Solid State Hybrid Drive (SSHD):

A hard drive with some solid state flash memory for storage
All data is stored on the hard drive

Size discrepancies

Unit prefixes for data sizes are power of 2 not 10

Storage is organised into file allocation units
- Unit size can vary between file systems, 4 KB is typical
- A file will occupy as many allocation units as it needs to store its data, but units cannot be divided or shared

Operating systems usually show “file size” and “size on disk”

“File size” can be any number of bytes
“Size on disk” can only be in multiples of the allocation unit size

Display Monitor (Size)

Measures diagonally, reported in (approx) inches
For example a MacBook Air has a 13” monitor size

Display Monitor (Resolution:)

Dimensions of the display, reported as “(number of pixels wide) x (number of pixels tall)”

Typical resolution:
4K
Full HD
HD

Display Monitor (Density:)

Sometimes size and resolutions are combined in a single “pixels per inch” (ppi) measure

LCD and LED

Most modern displays use a Liquid Crystal Display (LCD) panel and Light Emitting Diodes (LEDs) to produce the image on screen
LCD panel forms an image
LEDs provide backlight

Panel technology characteristics (Twisted Nematic (TN))

Accurate reproduction of fast moving images (e.g., gaming)

Colours appear distorted when viewed from off-centre angles

Panel technology characteristics (In Plane Switching (IPS))

Better reproduction of colour, especially when viewed from angles

Used in most contemporary displays, especially mobile devices

Input

Input devices allow users to provide information to the computer

E.g., keyboards, mice, trackpads, game controllers, webcams, microphones

output

Output devices allow computers to communicate information to users

E.g., displays, printer, speakers

Hybrid

Hybrids devices facilitate both input and output

E.g.,touchscreens

Touch Screens

Built into display (Types): Testable - Know This
Resistive
Capacitive

Can augment existing display:
Infrared
Surface acoustic wave

Resistive touch screens (*Testable - Know This)

Composed of two transparent sheets, separated by a gap

The sheets have electric charges in orthogonal directions

Pressure on the screen causes the sheets to touch each other, sending a signal indicating the position of the touch

Resistive Advantages/ disadvantages

Advantage:
Pressure from any object will activate a touch event
Low cost

Disadvantage
Vulnerable to scratches/damage

Capacitive Touch Screens (*Testable - Know This)

An electric field exists over the surface of the screen

Touching the screen disrupts this field

Grid of electrodes behind the screen detect the position(s) of touch

Capacitive Advantages/ disadvantages

Advantage:
More durable than resistive touch screens
Able to detect multiple touch points

Disadvantage:
Touch only activated with bare finger or conductive material

Embedded Systems

Computers that perform a limited range of functions

Typically act as part of a larger interconnected system