Hard Disk Drives (HDD)
Clusters.
A cluster is a group of multiple sectors. Clusters are also known as allocation units and are the smallest element of a drive to which an operating system can write.
Read/write head
A hard drive will have one read/write head for each platter side. This drive has two platters and four read/write heads.
PATA Connectors and Cables
All PATA connectors are 40-pin rectangular connectors, and they are the same on both the hard drive and the motherboard. Motherboards that support PATA typically have two connectors named IDE 1 and IDE 2 (or sometimes IDE 0 and IDE 1),Each ribbon cable includes three connectors—one for the motherboard IDE connection and two for the drives. In the figure, the two IDE connectors (IDE 1 and IDE 2) The maximum length of an IDE cable is 18 inches
SATA 3
Bit speed: 6.0 Gbit/s Byte speed: 600 MBps Names: SATA 6G, SATA 6Gb/s, SATA 6Gbit/s, SATA 600
Master and Slave Configuration
Each IDE connection supports two drives, and these are commonly identified as master and slave drives. The system will try to boot to the master drive, but it doesn't automatically know which drive to select. Instead, you have to manipulate jumpers on the drive to let the system know which drive is the master and which is the slave.
Tracks.
Each platter is logically divided into multiple tracks, which are circular areas on the disk. When the head is positioned over a track, it can read or write data on the track as the platter spins.
Files.
Files are written to clusters. If the file is bigger than a single cluster, the file is written to multiple clusters. Ideally, a file will be written to clusters that are next to each other, or contiguous clusters. However, if other data is already written on an adjoining cluster, the file is fragmented and written to another available cluster
Platters.
Hard drives have multiple spinning platters, and each platter can be written to on both sides.
RAID Not Found
Hardware RAID systems often come as external RAID enclosures, and when you first hook them up to a system, they might not be recognized. The most common reason is that the operating system doesn't have the drivers needed to use it. In this case, the solution is simple. Locate the drivers and install them. For new RAID systems, the manufacturer will include drivers. Follow the instructions that came with the device to install them. If it's not a new system, you can usually download the correct drivers from the manufacturer's website.
RAID Stops Working
If a RAID-0 has a failure in any single drive, it will stop working completely. You'll need to replace the drive, rebuild the array, and restore the data from a backup. However, other RAID arrays have built-in redundancy, so you usually won't see this symptom unless more than one drive fails.
ATA-6
Max Speed: 100 MBps Also called UDMA/100 and Ultra ATA/100 Maximum drive size increased to 144 PB
ATA-7
Max Speed: 133 MBps Also called UDMA/133 and Ultra ATA/133
ATA-4
Max Speed: 33 MBps Also called UDMA/33 and Ultra ATA/33
ATA-5
Max Speed: 66 MBps Also called UDMA/66 and Ultra ATA/66
PATA Speeds
PATA drives use direct memory access (DMA) transfers. DMA allows a device to directly access memory without the central processing unit (CPU), freeing up the CPU for other tasks. Ultra DMA (UDMA) appeared in ATA version 4 (ATA-4) and supported data transfers as high as 44 megabytes per second (MBps
HDD Physical Components
Platters. Read/write head. Actuator. Actuator arm and axis.
SATA Power Connectors and Cables
SATA power connectors have 15 pins, but the cables have only five wires. The color coding for the wires is as follows: Orange—3.3 V to pins 1, 2, and 3. Black—Ground to pins 4, 5, and 6. Red—5 V to pins 7, 8, and 9. Black—Ground for pins 10, 11, and 12. Pin 11 can be used to delay the startup of the drive or to indicate drive activity. Yellow—12 V to pins 13, 14, and 15.
SCSI ID
SCSI devices are controlled by a SCSI controller. Each device, including the controller, is assigned a SCSI identifier (SCSI ID) using numbers from 0 to 15. The controller is normally assigned the highest priority SCSI ID of 7.
SCSI
Small Computer System Interface (SCSI, pronounced scuzzy) is a drive interface standard that has been around as long as the earliest ATA standards. It has traditionally provided higher performance compared to the PATA drives, but it is more expensive and not widely used on desktop computers.
Ultra-160
Speed: bytes per second 160 MBps Speed: bits per second 1.28 Gbit/s
Ultra-320
Speed: bytes per second 320 MBps Speed: bits per second 2.56 Gbit/s
Ultra-640
Speed: bytes per second 640MBps Speed: bits per second 5.12 Gbit/s
Actuator arm and axis.
The actuator arm is moved back and forth by pivoting around the actuator axis. This positions the read/write head on different areas of the platter.
Actuator.
The actuator controls the movement of the arm.
Hard Drive Speeds
The rotational speed of the drive helps determine how quick it will be overall. Common speeds are 5,400, 7,200, 10,000, and 15,000 rpm. Drives with 7,200 rpm are used in standard desktop computers
Sectors
Tracks are logically separated into track sectors. A sector can be between 512 bytes and 2 KB in size.
Logical components:
Tracks. Sectors. Clusters. Files.
SCSI-2.
Uses a 25-pin, 50-pin, or 68-pin cable. This was first called fast SCSI because it could transfer data at 10 MBps, twice as fast as SCSI-1. It originally used an 8-bit bus. Fast-Wide SCSI is an update that uses a 16-bit bus and supports 16 devices with transfer rates of 20 MBps.
SCSI-3
Uses a 50-pin, 68-pin, or 80-pin cable. The most common cable is an 80-pin Single Connector Attachment (SCA). SCSI-3 is also called Ultra SCSI and includes several different versions
Read/Write Failure
When clusters on a hard drive fail, a hard drive is unable to read or write data to the cluster.Whenever you see errors related to hard disk reads and writes, it's safe to assume that there are problems with clusters on the drive. easy to overcome on Windowsbased systems, using simple tools such as chkdsk and Check Disk
BSOD
a stop error or blue screen of death (BSOD) from a hard drive or RAID problem. If it occurs, the most common reason is because the operating system doesn't have the correct driver for the drive. The most common solution is to boot into Safe Mode and install the correct driver.
Cable Select
allows the system to identify the drive based on which connector is used
SATA 1
bit speed: 1.5 Gbit/s Byte speed: 150 MBps Names: SATA 1.5G, SATA 1.5Gb/s, SATA 1.5Gbit/s, SATA 150
SATA 2
bit speed: 3.0 Gbit/s Byte speed: 300 MBps Names: SATA 3G, SATA 3Gb/s, SATA 3Gbit/s, SATA 300
SCSI-1
called narrow SCSI. Uses a 50-pin cable with a maximum transfer rate of 5 MBps. Narrow SCSI uses an 8-bit bus and supports a maximum of 8 devices
seek time
efers to the average amount of time it takes to move the read/write head from one track to another track, and lower seek times are better
PATA Power
hard drives use a standard four-pin Molex connector A four-wire cable from the power supply uses the following colors: Yellow 12 V Black ground (two middle wires) Red 5 V
SATA Data Connectors and Cables
include only seven wires, and cables can be as long as 1 meter (about 3.3 feet) A distinctive characteristic of SATA cables is that they have an L-shaped connector, which works as a key. Each drive is connected to a single SATA connector on the motherboard
Loud Clicking Noise
indicates that as the platter is spinning,it's hitting something it shouldn't. technicians often refer to it as a hard drive back up the data as quickly as possible and replace it.
Slow Performance
most common reason for a hard drive's performance to slow down is fragmentation the defrag and Disk Defragmenter tools that can check a disk for excessive fragmentation and that can defragment drives when they need it.
SCSI ID Priority Order
priority order from highest to lowest is as follows: ■ 7, 6, 5, 4, 3, 2, 1, 0, 15, 14, 13, 12, 11, 10, 9, and 8.
SATA
replaced PATA drives in almost all new systems. The newest version, SATA 6G, can transfer as much as 600 MBps. In contrast, PATA ATA-7 tops out at 133 MBps.
Failure to Boot/Operating System Not Found
system won't boot at all or gives an error indicating that it can't find the operating system, it could be that the bootable drive failed you'll need to replace it and rebuild the system. most common reason is that the system is trying to boot to a device that does not have a bootable operating system. If the system has floppy or optical drives, remove any disks/discs and then try to reboot. You might also need to check the BIOS to ensure that the system is configured to boot from the hard drive. If you see this problem after a system was recently worked on or a drive was replaced, double-check the cabling and jumpers.
Ultra SCSI
versions of SCSI-3. Each of these use a 16-bit bus and can support as many as 16 devices.
