Unit I : Evaluation of Computer System
Computers have become a vital part of our life. This Chapter introduces you to the computer and the way computer works. Different parts of the computer and how they work is also covered in this chapter.
Unit II : Hard Disk Drive
Unit III : Optical Media
Unit IV : Processor
Unit V : Hardware & Networking
New Trends in HDD
In terms of their basic design, today’s hard disks aren’t a lot different than the 10 MB clunkers installed in the first IBM PC/XTs in the early 1980s. However, in terms of their capacity, storage, reliability and other characteristics, hard drives have probably improved more than any other PC component. Let’s take a look at some of the trends in various important hard disk characteristics:
- Areal Density: The areal density of hard disk platters continues to increase at an amazing rate even exceeding some of the optimistic predictions of a few years ago. Densities in the lab are now exceeding 1.3 Tbits/in2 (2015) and modern disks are now packing as much as 20 GB of data onto a single 3.5″ platter!
- Capacity: Hard disk capacity continues to not only increase, but increase at an accelerating rate. From 10 MB in 1981, we are now well over 1TB and 14TB drive has already developed in 2017.
- Spindle Speed: The move to faster and faster spindle speeds continues. Since increasing the spindle speed improves both random-access and sequential performance, this is likely to continue. Once the domain of high-end SCSI drives, 7200 RPM spindles are now standard on mainstream IDE/ATA drives. A 15,000 RPM SCSI drive was announced by Seagate in early 2000.
- Form Factor: The trend in form factors is downward: to smaller and smaller drives. 5.25″ drives have now all but disappeared from the mainstream PC market, with 3.5″ drives dominating the desktop and server segment. In the mobile world, 2.5″ drives are the standard with smaller sizes becoming more prevalent; IBM in 1999 announced its Microdrive which is a tiny 170 MB or 340 MB device only an inch in diameter and less than 0.25″ thick! Over the next few years, desktop and server drives are likely to transition to the 2.5″ form factor as well. The primary reasons for this “shrinking trend” include the enhanced rigidity of smaller platters, reduction of mass to enable faster spin speeds, and improved reliability due to enhanced ease of manufacturing.
- Performance: Both positioning and transfer performance factors are improving. The speed with which data can be pulled from the disk is increasing more rapidly than positioning performance is improving, suggesting that over the next few years addressing seek time and latency will be the areas of greatest value to hard disk engineers.
- Reliability: The reliability of hard disks is improving slowly as manufacturers refine their processes and add new reliability-enhancing features, but this characteristic is not changing nearly as rapidly as the others above. One reason is that the technology is constantly changing, and the performance envelope constantly being pushed; it’s much harder to improve the reliability of a product when it is changing rapidly.
- RAID: Once the province of only high-end servers, the use of multiple disk arrays to improve performance and reliability is becoming increasingly common, and is now even seen in consumer desktop machines. Over the next few years I predict that RAID will become the “next big thing” as the thirst for performance increases, and in five years we may see new PCs commonly shipping with multiple hard disks configured as an array.
- Interfaces: Despite the introduction to the PC world of new interfaces such as IEEE-1394 and USB (universal serial bus) the mainstream interfaces in the PC world are the same as they were through the 1990s: IDE/ATA and SCSI. The interfaces themselves continue to create new and improved standards with higher maximum transfer rates, to match the increase in performance of the hard disks themselves.
Improvement of HDD Characteristics over the time: (source Wikipedia)
|Parameter||Started with (1956)||Developed to (2017)|
|Capacity||3.75 Megabyteas||14 Terabytes|
|Physical Volume||68 feet3 /1.9 m3||2.1 inches3 /34 cm3|
|Weight||910 KG||62 Gram|
|Average access time||approx. 600 milliseconds||2.5 ms to 10 ms; RW RAM dependent|
|Price||US$9,200 per megabyte (1961)||US$0.032 per gigabyte by 2015|
|Data density||2,000 bits per square inch||1.3 terabits per square inch in 2015|
|Average lifespan||~2000 hrs MTBF||~2500000 hrs MTBF|
MTBF : Mean time between failures (MTBF) is the predicted elapsed time between inherent failures of a mechanical system, during normal system operation. MTBF can be calculated as the arithmetic mean (average) time between failures of a system.