To run a program, it must first be loaded into memory (e.g. RAM)
Hard Dive (mechanical storage) vs SSD (electrical storage)
Memory is stored on a rotational platter that the head then seeks to to read/write
Electrical storage is generally faster and smaller
Not volatile storage (NVS) - memory that retains its information after losing power (Hard drives, etc.)
SSD (solid state drive) are faster than hard drives
Faster because they don’t rotate to get to a point on memory, and thus have no seek time
More expensive than HDDs, but consume lest power
Surface mounted on computer motherboards and acts as the main storage for mobile devices and some laptops
My thinkpad has a HDD (lsblk -o name, rota)
RAM drives - portions of RAM that are carved out as a block device and stored as a filesystem
/tmp, /dev/ram on linux
PCI Bus (Peripheral Component Interface) - A data bus connecting hardware components on a computer
A disk may have some bad blocks which are unusable. It keeps track of these bad blocks throughout its lifetime. Generally there are additional sectors that are logically replaced (what the OS sees) when these blocks go bad
It takes time to seek to and retrieve memory - we can reduce this latency with scheduling algorithms
Note: These only make sense for hard drives since the disk is physically spinning
Generally reads/writes in sequential order perform better on hard drives due to the lower seeking time
Linux deadline scheduler
Implements a CSCAN algorithm (start at the start of the disk, process to one end, then immediately come back) and maintains separate read and write queues
Each drive has a queue of operations. If it is busy, an IO request is appended to the queue
The OS must write it’s own data structures to the device before it can use it
First, Partitioning - Breaks the device up into one or more groups of blocks or pages
Each partition can be treated as a separate device
In Linux, if a drive is recognized, it’s partition info is read, and separate entries for the partitions are created in the /dev directory
The /etc/fstab configuration file then tells the OS to mount each partition containing a filesystem at a given point (mounting is just making the filesystem available to users - I’ve heard a lot of definitions of mounting and think this is the simplest)
Next, volumes are created from the partitions to be mounted (partitions are a logical device-specific thing, volumes are software)
Lastly, Logical formatting - The creation of a file system. The OS stores file-system data structures on the device (e.g. maps of free and allocated memory as well as an empty directory)
A bootable filesystem contains OS code (partition labeled for boot -> used to establish the root filesystem on which other devices are mounted in Linux)
Raw disk Special programs can access a partition as a sequential sequence of logical blocks with no file system data structures -> this is raw disk (and uses raw I/O) and is used for swap space
Raw I/O bypasses all file system services like prefetching, filenames, directories, etc.
Some databases use raw IO because they can specify exactly where things are stored
Bootstrap program is stored in flash memory (essentially EEPROM)
Generally the bootstrap loader (stored in flash memory) loads in a full bootstrap program into secondary storage
The bootstrap loader is grub for linux
The full bootstrap program is stored at a fix memory location - the bootstrap loader instructs the hardware to load the program into memory. The full program then loads the OS
MBR (Master Boot Record) - Where bootstrap code is stored
