Computer Hard Drive

Introduction The hard drive of a computer is a device that stores all the software installed on a computer, as well as all the data files created and used by this software. This includes any documents you have created and downloaded, such as photos and music. The hard drive is a form of permanent storage, rather than temporary memory such as random-access memory (RAM).

Types of Hard Drives Technologies There are two general types of hard drives: hard disk drives (HDD), which use one or more rotating discs and rely on magnetic storage, and solid-state drives (SDD), which have no moving mechanical parts, but use flash memory like the kind found in USB flash drives. If you have a regular desktop computer, you most likely have a hard disk drive. Solid-state drives are used more typical for high-end, expensive laptops.

Hard Disk Drive

Solid State Drive

Basic Features of Hard Disk Capacity Revolutions Per Minute, (RPM) Form Factor Disk Buffer Interface Type

Capacity Capacity is the maximum amount of data a hard disk can store. Typical hard disk storage capacities today are either in gigabytes or terabytes. These sizes store enormous amounts of data and this is very useful when saving music and video, especially video files, which can get very large. In 2014 Seagate produced the world’s first 8 Terabytes Hard disk and in 2016 it produced the world’s largest disk i.e. 60TB SSD. Samsung produced a 15 SSD in 2015

Revolutions Per Minute (RPM) Within a hard disk case are round platters (the actual disks) that are attached to a spindle that spins. The disks are written to or read from while spinning. One revolution is how many times the platters make a complete rotation. Stored in sectors and tracks Disks in a HDD literally rotate thousands of times per minute. The greater the RPM, the faster data is read or written. 7200 RPM is typically what you will see in most computer hard drives.  High end server hard disk typically have 15,000 RPM

Hard Disk Drive

Solid State Drive

Form Factor: The form factor of a hard drive is the actual physical size of the case the platters are in. The main sizes are 3.5inches for desktop and 2.5inches for laptop It  doesn’t actually refer to the physical measurement of width or height of the drive, but refers to the size of the drive bay of the computer. 

Disk Buffer: It is a small amount of memory, usually 8, 16, or 32MB, which is set aside for the most frequently accessed files. When one of these frequently used files is selected, it is retrieved from the buffer and this reduces access time since the system does not have to search the entire drive for the data.   Again buffer, temporarily stores data while the data is the process of moving from one place to another, i.e. the input device to the output device

Interface Type The primary job of the hard disk controller or interface is to transmit and receive data to and from the drive. The different interface types limit how fast data can be moved from the drive to the system and offer different levels of performance The three main type of interface are Integrated Drive Electronics (IDE) Serial Advanced Technology Attachment (SATA) Small Computer Systems Interface( SCSI)

IDE (Integrated Drive Electronics): The IDE standard has been around for a very long time but as improvements were developed it later was called Enhanced IDE (EIDE) and even further developments brought about Advanced Technology Attachment (ATA). These drives connect to the motherboard via a flat, 40 or 80-wire cable to an IDE connector. It enables two drives to be attached on one cable. 

IDE Cable

IDE The speed of a hard drive is determined by how fast the interface can send data. The primary drive rates between 100 MB/s and 133 MB/s with 133 MB/s being the maximum. These hard disks are commonly described by the abbreviation "ATA" followed by the speed of its connector (ATA 100, ATA 133).  IDE drive connectors use a parallel bus, meaning multiple bits are transmitted simultaneously. To distinguish between Serial ATA drives, IDE disks are also referred to as PATA (the "P" stands for parallel). 

Serial Advanced Technology Attachment (SATA): SATA disk drives are the current standard and use a serial interface to transfer data, i.e. data is transmitted one bit at a time which is faster than sending several bits at a time as with IDE. Data travels along a single wire, reducing interference hence one path is used for sending and another for receiving. 

SATA The original SATA standard had a transfer rate of 150 Mb/s (SATA-150). Now SATA can transmit up to 3 Gb/s (SATA 2), and 6 Gb/s (SATA 3). SATA uses a 7-wire cable for connecting to the motherboard. 

Features of SATA Reduced cable size ( 7 wires instead of 40 or 80) Faster data transfer Hot swapping feature (replacing faulty component while system is running without disruption to the system) Hot plugging (addition of components while system is running to increase the functionality of the system)

SCSI Drive SCSI (Pronounced "scuzzy") stands for Small Computer Systems Interface, and was originally developed to replace IDE before SATA was developed. SCSI is much faster than IDE but are a little more troublesome to configure than IDE and SATA and generally tend to be more expensive. They however spin at a higher rate in comparison to IDE and SATA ones. IDE and SATA drives generally spin at 7,200 rpm, whereas SCSI drives spin at 10,000 to 15,000 rpm. 

SCSI Interface

External Hard Drive Hard disk drives can connect externally to a computer. The drive is placed in a case called an enclosure that contains a port(s) on the back for connecting to the computer via a cable. For quite some time enclosures used USB or Firewire ports. Now, many support any combination of USB, Firewire, and External SATA (eSATA) ports on the same encasement. External SATA is far faster than USB and Firewire. To use it, a computer must also have an eSATA connector. If it doesn't, a card can be purchased with the interface on it. Enclosures are manufactured to match the form factor of particular drive. 

Storage Area Network It’s a collection of hard disk in a self-contained unit. Typically used in a large network environment, SANs serve as pools of storage for the servers in the network. Compared to managing disks attached to each server, SANs improves system administration by treating all array of disk as a single resource makes disk maintenance and routine backups easier to schedule and control. To support disaster recovery, redundant SANs are deployed in separate locations, each as a copy of the other.

HP SAN System

Partitioning a Hard Drive Partitioning simply mean dividing a single hard disk into multiple logical drives such that each drive behaves like a single hard disk. There are 3 main types of partition Primary Partition It is where the operating system will be stored and booted from Extended Partition Primary partition that has been prepared to contain logical drives i.e. setting space aside to create logical drives later Logical Drives Partition created inside an extended partition

Formatting a hard drive Formatting means configuring the disk with a file system so that the operating system can store information on the disk. It also create tracks and sectors on the platters. A sector contains a fixed number of bytes. A file system is used by the operating system to organize and keep track of files.  Without a file system, information stored on a hard disk would be one large body of data with no way to tell where one piece of information stops and where the next begins. 

Types of Filing System in Windows New Technology Filing System (NTFS)  It supports long file names, large volumes, data security, and universal file sharing File Allocation Table (FAT32)  It an old system which is unable to deliver the same performance, reliability and scalability as NTFS.

Other Hard Disk Functionalities and Feature Disk Fragmentation process of locating the noncontiguous fragments of data into which a computer file may be divided as it is stored on a hard disk, and rearranging the fragments and restoring them into the whole file. Redundant Array of Independent Disk (RAID) Storing of the same data across 2 or more hard disks. E.g. RAID 0, RIAD 1, RAID 5, RAID 10 Disk Quota It is the allocation of a specific amount of disk space to individual users on a network

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