Hard Disk Drives
Hard disk drives are often referred to as “mass storage devices” – they can hold a large amount of data and in the context of this section, are “fixed” – installed in a PC. Later, we will discuss external hard disk drives. In early PCs, hard disk drives were measured in megabytes, now it’s mostly gigabytes, though manufacturers are breaking the terabyte level on some newer drives.
Figure 2: Hard Disk Drive
Figure 3: The Insides of a Hard Disk Drive
Hard drives come in many different physical sizes, speeds, and connector types. The guts of a hard drive are all basically the same: it contains one or more platters with a head which reads data. You will often hear speed described in RPM: 5400RPM, 7200RPM, 10,000RPM, and even 15,000RPM. The higher the number, the faster the drive spins the platter and can read data. Typically you will only see 10,000RPM (also called 10K) and 15,000RPM (15k) drives in servers or high-end workstations.
Speed is also measured by the data transfer speeds which is limited by the type of connector the hard drive uses. We will discuss speeds with each connector section.
Hot-Swappable
Most Hard Drives are fixed inside desktop PCs, but servers frequently contain hot-swappable hard drives. A hot-swappable drive is mounted inside a special drive cage which can be pulled out and replaced while the server is on. You don’t want to remove a hard drive from a desktop PC while it is still running!
Hot-swappable drives are important in servers as uptime is extremely important. Most server configurations use some sort of redundant drives (RAID technology) to have data spread across multiple drives. In a RAID 5 configuration, for example, you can have one drive fail and the data will be safe. A hot-swappable drive can be replaced and rebuilt in the array without shutting down the server. You won’t need to know all of this for the exam, but be familiar with the term hot-swappable and what it means.
Hard Drive Connectors
In a couple of sections, we will discuss several different connector types on the motherboard or add-on cards for connecting drives. In this section, we are going to discuss those connector and cable types in detail so you can understand them for the exam. There are basically three types of connector types you need to be aware of for the exam: IDE (EIDE), SATA, and SCSI.
IDE (EIDE/PATA)
For years, IDE and its successor EIDE were the most popular drive adapter types on the market. It is still in use and is frequently used to connect CD-ROM and DVD-ROM drives even if your system has SATA or SCSI for the hard drives.
Figure 4: IDE Ribbon Cable
Figure 5: IDE Rounded Cable
IDE refers to the ATA technology specification. Another name for the ATA disk drive technology is Parallel ATA, or PATA, compared with our next drive connector type Serial ATA (SATA).
Figure 6: 4 Pin Molex Power Connector - ATA Drives
ATA has several different versions which all use the connector and cables shown above.
ATA: Commonly referred to as an IDE connection, ATA supports a maximum of 2 drives. It is a 16-bit interface.
ATA-2: Sold as Fast ATA or Enhanced IDE (EIDE), ATA-2 supports block transfers and logical block addressing.
Ultra-ATA: Supports speeds of 33 Megabits per second.
ATA/66: Developed by Quantum and supported by Intel, doubles ATA throughput to 66 Mbps.
ATA/100: Most frequently used today – supports up to 100 Mbps.
SATA (Serial ATA)
Serial ATA is an evolution of the Parallel ATA connectors we discussed above (in the form of IDE). Serial ATA cables are smaller allowing for easier airflow in computers. Additionally, they are faster than ATA with speeds at 150 Megabytes per second and 300 Megabytes per second (1.5 Gbits and 3.0 Gbits respectively).
Figure 7: SATA Connection Cable
With a much higher data transfer rates, you can take advantage of faster hard drives with SATA. My workstation has a 150GB 10,000 RPM Seagate Cheetah drive as the boot drive – very fast!
SATA also supports hot pluggable drives while Parallel ATA does not. For this reason, SATA has replaced some of the lead SCSI has in the server market, allowing server vendors to reduce some cost in their server systems.
Figure 8: SATA Power Connector
Whereas the ATA drives use a 4 pin molex power connector, most SATA drives use a new flat style power cable.
SCSI
Small Computer System Interface, or SCSI, has been around for a long time in the computer industry. Once the only interface on Apple Macintosh systems and still used in a variety of servers and workstations, SCSI is a very reliable and fast connector which is frequently used in RAID configurations with multiple hard drives for redundancy.
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