Top 10 List of Week 09

1. Volatile vs Non Volatile Memory

2. Hard Disk Drives (HDD) Scheduling

First Come First Serve (FCFS) : This algorithm is fair as it allows all requests a chance but it does not provide the fastest possible service. To determine the number of head movements you would simply find the number of tracks it took to move from one request to the next.
SCAN : The head moves towards one direction while servicing all the requests in that direction until it reaches the end of the disk.
C-SCAN : It’s circular SCAN. Once it hits the end it jumps to the other end and moves in the same direction.
LOOK : In this algorithm, the head moves towards one direction while servicing all the requests in that direction until it reaches the last request. After that it starts moving towards the other direction.

3. Non-Volatile Memory (NVM) Scheduling

NVM doesn’t contain moving disk heads and commonly uses an FCFS policy, but modifies it into merge adjacent requests.

4. Error Detection and Correction

This is a fundamental aspect of many parts of computing. Error detection determines if there a problem has occurred by parity bit or cyclic redundancy check (CRC) which uses hash function to detect multiple bit errors. Error-correction code (ECC) not only detects, but can correct some errors (only soft errors).

5. Disk Formatting

Disk formatting is a process to configure the data-storage devices when we are going to use them for the very first time or we can say initial usage.We can perform disk formatting on both magnetic platter hard-drives and solid-state drives. Formatting process of disk:

Low-level Formatting : Physical Formatting
Partitioning : Divding hard-disk into multiple regions
High-level Fromatting : Writing

6. Boot Block

A computer needs an initial program to run, this initial program is called bootstrap. This program must initialize all aspects of the system. Bootstrap finds the OS kernel in disk and then loads the kernel into memory anf then jumps back to the initial address to begin excecuting. Bootstrap usually stored in ROM. The problem is that changing the bootstrap code basically requires changes in the ROM hardware chips. ecause of this reason, most system nowadays has the tiny bootstrap loader program in the boot whose only job is to bring the full bootstrap program from the disk. Meanwhile Full bootstrap program is stored in the boot blocks at a fixed location on the disk.

7. Bad Block

Because disks have moving parts and small tolerances, they are more prone to failure. Sometimes the failure/ damage is complete; in this case, the disk needs to be replaced. This is what we call bad block. There are 2 types of bad block:

Physical or Hard bad block : damage to the storage hardware
Soft or Logical bad block : the OS is unable to read data from a sector There are couple of ways to handle bad blocks, like manual and sector sparing/forwarding and sector slipping.

8. Swap-space Management

Swap space is the area on the disk where the swapped out processes are stored is called swap space.The goal of swap-space implementation is to provide the virtual memory the best throughput. There are two approach to implement swap-space, normal file-system and raw partition.

Normal file-system : easy to implement, but inefficient.
Raw partition : There is no presence of any file system in this place. Rather, a swap space storage manager is used to allocate and de-allocate the blocks.

9. Storage Attachment

Computers access secondary storage in 3 ways:

Host-Attached Storage : Accesed through local I/O ports.These ports use several technologies, the most common being SATA.
Network-Attached Storage : Provides access to storage accross a network. Clients access this storage via remote-procedure-call interface like NFS for UNIX or CIFS for Windows
Cloud Storage : Also provides access to storage accross a network, but clients access the storage via the Internet or another WAN to a remote data center that provides the storage.

10. RAID (Redundant Arrays of Independent Disks)

Because of the amount of storage required on large systems, and because storage devices fail in various ways, secondary storage devices are frequently made redundant via RAID algorithms. This algorithm which makes use of a combination of multiple disks instead of using a single disk for increased performance, data redundancy or both. Key evaluation points for a RAID algorithm:

Reliability
Availability
Performance
Capacity