Hard drives are the weak link of a computer. They are considered a secondary storage device and memory is primary. Hard drive data throughput (bandwidth or speed which data moves) ranges from about 50MB (mega bytes or million bytes) to about 200MB per second. RAM however is 3+GB (giga bytes or billion bytes) per second. This means that hard drives are 50+ times slower than RAM memory. Therefore when your computer has to read/write files to your hard drive things come to almost a stop for the very fast CPU. Hard drives have not been able to keep up with the growing demands of bandwidth. Also the hard drive is a mechanical device prone to premature failure and maintenance needs. SATA drives have only doubled the bandwidth to about 100MB per second. Solid-state drives are coming down in price and again have doubled the bandwidth to about 200MB per second. Therefore, solid state drives, with no moving parts, 1,500,000 hours of mean time between failures are the future for secondary storage needs. The bandwidth has more opportunity to improve without all the limitations of moving parts.

File information is stored on the drives in clusters (see figure). Clusters are made up of sectors that are on tracks/cylinders. It is important to understand that a sector is always 512 bytes and files are stored in clusters, which are made up of sectors. A test question is what is the smallest storage area on a drive? It is not a sector but a cluster. The number of sectors in a cluster can vary depending on how the drive was formatted. Large cluster sizes provide faster file reading/writing but can waste a lot of storage space. For the large hard drives we have today the cluster size (also called allocation unit size) is usually 4096 bytes or 8 sectors (512x8=4096). If you were to save a file that is only 1000 bytes you would lose 3096 bytes of storage space, because the smallest storage space is 4096 bytes (cluster size). Tracks/cylinders are also important to understand. A track is a concentric circle that is formatted on the drive and divided into sectors for data storage. Cylinders are more than one track (cylinders are formed from concentric circles). The total storage space of a drive can be figured if you know total number sectors. Remember, the sector is always 512 bytes. So it's easy to figure out storage space if you can figure out the total sectors on a drive. Fragmentation becomes a problem because files a stored end to end (contiguous) on the tracks. If you delete a file it leaves a hole in the track that will be filled with other files. Files are never the same size so two different holes might be used to store the next file. Now you have a fragmented file because the file is not in a nest little row, but scattered over the drive. As the hard drive is used fragmentation gets worse until the drive can no longer keep up with the demands and errors begin. This will cause the operating system to slow down, become unstable, and hang and/or crash (see video below). It is important to check your drives from time to time and defrag the drive as necessary. Defragging will speed up the computer and extend the hard drives life. Windows does not have any self-maintenance tools so installing a utility like Smart Defrag can be very helpful. Smart Defrag (free download) runs very nicely in the background and will defrag your drive during low CPU usage automatically. You will never know its doing it's job and keeping your drive running at its optimum.

Since reliability and speed are big concerns with hard drives RAID technology has helped to improve both concerns. RAID 0 allows drive spanning. This allows for faster read write by spreading the data through more than one channel. With just 2 drives you can increase the bandwidth considerably, but if one drive fails you lose all the data. RAID 1 allows for mirroring data between 2 drive but no bandwidth improvement. RAID 5 allows for improved reliability and speed improvement with 3 or more drives. RAID 10 is a combination of RAID 0 and 1 (1+0). Some motherboards have RAID features built-in. Microsoft has software utilities built-in to their server software.

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