Chapter 7 Flashcards
hard drives
Traditional mechanical hard drives are magnetic hard drives. These hard drives have multiple hard metal surfaces called platters. Each platter typically holds data on both sides and has two read/write heads, one for the top and one for the bottom. The read/write heads float on a cushion of air without touching the platter surface. Data is written by using electromagnetism. A charge is applied to the read/write head creating a magnetic field. The metal hard drive platter has magnetic particles that are affected by the read/write head’s magnetic field allowing 1s and 0s to be “placed” or “induced” onto the drive, (Schmidt 253)
head crash
If a read/write head touches the platter, a head crash occurs. This is sometimes called HDI (head-to-disk interference), and it can damage the platters or the read/write head, causing corrupt data. (Schmidt 254)
cylinder and tracks
he hard drive surface is metallic and has concentric circles, each of which is called a track. Tracks are numbered starting with the outermost track, which is called track 0. One corresponding track on all surfaces of a hard drive is a cylinder. For example, cylinder 0 consists of all track 0s; all of the track 1s comprise cylinder 1, and so on. A track is a single circle on one platter. A cylinder is the same track on all platters (Schmidt 255)
sector
Each track is separated into sectors, with the circle divided into smaller pieces. Normally, each sector stores 512 bytes (Schmidt 256)
hard drive interface
A hard drive system must have a set of rules to operate. These rules specify the number of heads on the drive, what commands the drive responds to, the cables used with the drive, the number of devices supported, the number of data bits transferred at one time, and so on. These rules make up a standard called an interface that governs communication with the hard drive. There are two major hard drive interfaces: IDE (integrated drive electronics), also known as the ATA (AT Attachment) or EIDE (Enhanced IDE) standard, and SCSI (Small Computer System Interface). IDE is the most common in home and office computers. SCSI is commonly found in network servers. (Schmidt 257-258)
parallel communication of hard drives
Both IDE and SCSI started out as parallel architectures. This means that multiple bits are sent over multiple paths. This architecture requires precise timing as transfer rates increase. Also with both types of devices, multiple devices can attach to the same bus. With parallel IDE or PATA (Parallel ATA), it was only two devices and with SCSI it was more, but the concept is the same. When multiple devices share the same bus, they have to wait their turn to access the bus and there are configuration issues with which to contend (Schmidt 258)
serial communication of hard drives
Both the IDE and SCSI standards have a serial architecture available. The ATA serial device is known as a SATA (Serial ATA) device, and the serial SCSI serial device is known as a SAS (Serial Attached SCSI) device. A serial architecture is a point-to-point bus where each device has a single connection back to the controller. Bits are sent one at a time over a single link. More devices can attach to this type of architecture because it scales easier and configuration is much easier (Schmidt 258)
IDE
IDE (Integrated Drive Electronics) is not only for traditional mechanical hard drives but for other internal devices, such as tape, Zip, and optical drives. The original IDE standard was developed only f or hard drives and is officially known as ATA (AT Attachment). Later, other devices were supported by the standard and the standard evolved to ATA/ATAPI (AT Attachment Packet Interface). ATAPI increased support of devices such as CD/DVD and tape drives. There are two types of ATA—PATA (Parallel ATA) and SATA (Serial ATA). (Schmidt 259)
PATA
PATA is the older IDE/EIDE type, which uses a 40-pin cable that connects the hard drive to an adapter or the motherboard and transfers 16 bits of data at a time. Each cable normally has either two or three connectors. Many motherboards have both SATA and PATA IDE connectors (Schmidt 259)
ATA-5
The original IDE interface supported up to two drives and is also known as the ATA-1 Standard (AT Attachment Standard). The ATA-5 standard (also known as Ultra ATA/66 or ATA/66) was important because the PATA cable changed. A 40-pin cable is used with this standard as with the other standards, but the cable is different—it has 80 conductors. The 40 extra conductors are ground lines, which are situated between the existing 40 wires. These ground lines reduce crosstalk, improves the accuracy of data transfers, and allows faster speed. Signals from one wire can interfere with the signals on an adjacent wire; this is called crosstalk (Schmidt 260)
SATA types
The original IDE interface supported up to two drives and is also known as the ATA-1 Standard (AT Attachment Standard). The ATA-5 standard (also known as Ultra ATA/66 or ATA/66) was important because the PATA cable changed. A 40-pin cable is used with this standard as with the other standards, but the cable is different—it has 80 conductors. The 40 extra conductors are ground lines, which are situated between the existing 40 wires. These ground lines reduce crosstalk, improves the accuracy of data transfers, and allows faster speed. Signals from one wire can interfere with the signals on an adjacent wire; this is called crosstalk (Schmidt 260)
SATA
SATA is a point-to-point interface, which means that (1) each device connects to the host through a dedicated link (unlike the traditional parallel IDE where two devices share the host link), and (2) each device has the entire interface bandwidth. SATA uses a smaller, 7-pin cable that is more like a network cable than the traditional IDE ribbon cable. SATA supports both internal and external devices. (Schmidt 261)
eSATA
eSATA (External SATA) provides external device connectivity using the SATA standard. allows shielded cable lengths up to 6.56 feet (2 meters), with faster connections than USB 2.0 or most IEEE 1394 types. However, the standard eSATA connection does not provide power to external devices, but an eSATAp combo USB/eSATA port can provide power. (Schmidt 262)
SSD
SSDs (solid state drives) are storage devices that use nonvolatile flash memory technologies instead of hard drive technologies. SSDs connect to the computer through several types of interfaces: SATA, SAS, PCIe, USB, PATA, and SCSI. SSDs eliminate the number-one cause of hard drive failure: moving parts. SSDs typically use flash memory and can therefore be low heat producing, reliable, quiet, secure, long-lasting, and fast. (Schmidt 263)
SSD write amplification
Write amplification is the minimum amount of memory storage space affected by a write request. For example, if there is 4KB of information to be written and the SSD has a 128KB erase block, 128KB must be erased before the 4KB of information can be written. Writing takes longer than reading with SSDs. (Schmidt 263)
