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+#let title = [
+  *Unit 3: Physical Layer*
+]
+#set text(12pt)
+#set page(
+  header: [ 
+    #box()[
+      _*Knowledge not shared, remains unknown.*_
+    ]
+    #h(1fr)
+    #box()[#title]
+  ],
+  numbering: "1 of 1",
+)
+#align(center, text(20pt)[
+  *#title*
+])
+#show table.cell.where(y: 0): strong
+#outline()
+#pagebreak()
+= Physical Layer Overview
+_Physical compute systems host applications that a provider offers as services to consumers and also execute the software used by the provider to manage the cloud infrastructure and deliver services._
+- Consists of compute, storage and network resources.
+- A provider offers compute systems to consumers to execute their own applications.
+- Storage systems store business data, and data generated or processed by them.
+- Networks connect various compute systems and storage systems with each other.
+- Networks can also connect various clouds to one another.
+= Compute
+_A compute system is a computing platform that runs platform and application software._
+- Consists of the following:
+  1. Processors
+  2. Memory
+  3. IO devices
+  4. OS
+  5. File system
+  6. Logical volume manager
+  7. Device drivers
+- Providers typically deploy on x86 hosts.
+- Compute systems provided in two main ways:
+  - *Shared hosting*: Multiple consumers share compute systems.
+  - *Dedicated hosting*: Individual consumers have decided compute systems.
+- Compute virtualization is usually used to create virtual compute.
+== Key components of compute system
+1. *Processor*
+  - IC that executes the instructions of software by performing:
+    - Arithmetical operations
+    - Logical operations
+    - Input/Output operations
+  - x86 is a common architecture used with 32 and 64 bit varients.
+  - Many have multiple cores capable of functioning as individual processors.
+2. *RAM*
+  - Volatile internal data storage
+  - Holds software programs and for execution and data used by the processor.
+3. *ROM*
+  - Semiconductor memory containing:
+    - Boot firmware
+    - Power management firmware
+    - Device specific firmware
+4. *Motherboard*
+  - PCB on which all compute systems connect
+  - Contains sockets to hold components
+  - Contains network ports, I/O ports, etc.
+  - May contain additional integrated componentsts such as GPU, NIC, and adapters to connect storage drives.
+5. *Chipset*
+  - Collection of microchips on a motherboard designed to perform specific functions.
+  - Two main types are:
+    - _Nothbridge_: Manages processor access to RAM and GPU
+    - _Southbridge_: Connects processor to peripheral ports
+== Software on Compute Systems
+#table(
+  columns: (auto,auto),
+  table.header([Methodology], [Description]),
+  [Self-service portal], [Enables consumers to view and request cloud services],
+  [Platform software], [Includes software that the provider offers through PaaS],
+  [Application software], [Includes application that the provider offers through SaaS],
+  [Virtualization software], [Enables resource pooling and creating of virtual resources],
+  [Cloud management software], [Enables a provider to manage the cloud infrastructure and services],
+  [Consumer software], [Includes a consumer's platform software and business applications]
+)
+== Types of compute systems
+=== Tower compute system
+- Built in an upright enclosure called "tower".
+- Has integrated power and cooling.
+- Require significant floorspace, complex cabling and generate a lot of noise.
+- Deploying in large environments may require substancial expenditure.
+=== Rack compute system
+- Designed to fit on a frame called "rack".
+- A rack is a standardized system enclosure containing multiple mounting slots called "bays", each holding a server with the help of screws.
+- A single rack contains multiple servers stacked.
+  - This simplifies network cabling, consolidates network equipment and reduces floorspace use.
+- Each rack has it's own power and cooling.
+- Administrators may use a console mounted on the rack to manage the computer systems.
+- Cumbersome to work with, generate a lot of heat, increased power costs. 
+=== Blade compute system
+- Electronic circuit board containing only core processing components.
+- Each is a self contained compute system dedicated to a single application.
+- Housed inside a blade enclosure which holds multiple blade servers.
+- Blade enclosures provide power, cooling, networking, management functions.
+- The modular design minimizes floorspace usage, increases compute density and scalability.
+- Best energy effeciency.
+- Simplifies compute infrastructure management.
+- High in cost and proprietary architecture.
+= Storage
+_Data created by individuals, businesses, and applications needs to be persistently stored so that it can be retrieved when required for processing or analysis. A storage system is a repository for saving and retrieving data._
+- Providers offer storage capacity along with compute systems, or as a service.
+- Storage as a service allows for data backup and long term data retention.
+- Cloud storage provides massive scalability and rapid elasticity.
+- Typically, a provider used virtualization to create storage pools that are shared by multiple consumers.
+== Types of Storage Devices
+#table(
+  columns: (auto, auto),
+  table.header([Type], [Description]),
+  [Magnetic disk drive], [
+    - Stores data on a circular disk wirh a ferromagnetic coating.
+    - Provides random read/write access.
+    - Most popular storage device with large storage capacity.
+  ], [Solid-State drive], [
+    - Stores data on a Semiconductor-based memory.
+    - Very low-latency per I/O, low power requirements, and very high throughput.
+  ], [Magnetic tape drive], [
+    - Stores data on a thin plastic film with a magnetic coating.
+    - Provides only sequential data access.
+    - Low-cost solution for long-term data storage.
+  ], [Optical disk drive], [
+    - Stores data on a polycarbonate disk with a reflective coating.
+    - Write once and read many capability: CD, DVD, BD.
+    - Low-cost solution for long-term storage.
+  ]
+)
+== Redundant Array of Independent Disks
+_RAID is a storage technology in which data is written in blocks across multiple disk drives that are combined into a logical unit called a RAID group._
+- Improves storage system performance as I/O is served simultaneously across multiple disks.
+- Implemented using a specialized hardware controller present on the host or the array.
+- Functions of RAID are:
+  1. Management and control of drive aggregations
+  2. Translations of I/O requests between logical and physical drives.
+  3. Data regeneration in the event of drive failures.
+=== Types of RAID
+==== Striping
+#figure(
+  image("./images/striping.png")
+)
+_Striping is a technique to spread data across multiple drives in order to use drives in parallel and increase performance as compared to the use of a single drive._
+- Each drive as a predefined numbwe of contiguously addressable blocks called a strip.
+- Stripe is a set of aligned strips that span across all the drives.
+- All strips in a stripe have the same number of blocks.
+- Does not provide any data protection.
+==== Mirroring
+#figure(
+  image("./images/mirroring.png")
+)
+_Mirroring is a technique in which the same data is stored simultainously in two different drives, resulting in two copies of data. This is called a "Mirrored Pair"._
+- Even if one fails, the data is safe in the surviving drive.
+- When a failed disk is replaced, the controller copies the data from the surviving drive to the mirrored pair.
+- Mirroring provides the following:
+  - Data redundency
+  - Fast recovery from disk failure
+- Twice the number of drives are required.
+- Increase in costs.
+- Mirroring used for mission critical operations.
+- Better read performance, worse write performance.
+==== Parity
+_Parity is a RAID technique to protect striped data from drive failure by performing a mathematical operation on individual strips and storing the result on a portion of the RAID group._
+- RAID controller finds parity using techniques like XOR.
+- Parity data can be stored on seperate drives or distributed across drives in a RAID group.
+- Parity is calculated everytime data is modified.