Hard Drives (continued...)

Five Main Components
Platters - The aluminum alloy disks upon which data is stored. It's a magnetic media, somewhat akin to the surface preparation on a cassette tape. However, the surface of the platter is magnetically formatted (on both sides) into sectors and tracks where digital information is written.

Spindle - the platters or disks spin on the spindle, which is run by a motor on the drive. I guess you could say it's kind of like the axle on a wheel.

Read/Write Heads - The heads move across the platters to write data to, and read data from the platters. There's a read/write head for each side of each platter. Access is random, meaning that the heads can jump straight to the information they want without having to fast-forward or rewind past unneeded information.

Head Actuator - Controls the read/write heads. The heads are at the end of an actuator arm which is attached to the actuator.

Circuit board - Receives commands from the hard drive controller and translates them in order to move the head actuator, which moves the read/write head across the platters to the required position.

Organization
Low Level Formatting - Low-level formatting divides the surface of the disk into tracks and sectors. This sets up a kind of a grid so that the controller knows how to access each individual sector. For instance, it might store part of a file at 'head #2, track 40, sector 16'. It's almost like a 3D game of battleships.

It used to be necessary to individually low-level format the older drives before they could be used by your computer. This is no longer the case. On all the drives you'll see (unless you're working on a very old computer), low-level formatting is done at the factory. You may see a choice in your CMOS setup program called 'Low-Level Format'. I would suggest against using it. It's a dinosaur from days gone by.

There are, however, 3rd party programs which claim to safely low-level format IDE and EIDE hard drives. If you wish to try them, that's your choice. I'm certainly not one to discourage experimentation. Just take into consideration the value of the data you plan on storing on them afterwards, and the fact that the manufacturers recommend against it.

Tracks - When a read/write head is stationary, the area that spins directly under the head is called a track. There is the same number of tracks on both sides of each platter in a hard drive. Each track forms a complete circle, unlike a vinyl record, which has a single track that spirals to the center.

Cylinders - The read/write heads all move on the actuator arm together. So they're all positioned over the same track, on each side of each disk, simultaneously. The entire set of tracks moving under all the heads when they're stationary makes up a cylinder. If the platters in a drive each have 968 tracks, then there are 968 cylinders. Data is written from the outside cylinder inwards, using up space on each cylinder before the heads move to the next track, or next cylinder.

Sectors - Each track is divided up into 512 byte blocks called sectors. The data written to your drive is stored in these sectors, a cluster at a time.

Clusters - A defined number of sectors make up a cluster. The number of sectors in each cluster varies depending upon the size of the HD (Hard Drive) and how it's partitioned.

How come?
Well, a cluster is the smallest allocation unit that can be written to the hard drive. Your computer needs an index, or a map telling where each cluster is, and what's stored there. This index is called the File Allocation Table (more on the FAT later). The FAT has a limited size. In other words, it can only count so many clusters. It doesn't care how big the clusters are, but it can only count so many. So, as the size of the drive increases, the number of sectors in each cluster has to increase, to keep the number of clusters the same.

This means that if a cluster is made up of 32 sectors, even a 1 byte file is going to take up 16,384 bytes or 16K of storage space (32 X 512 bytes). Or, if you have a file that is 16,385 bytes, it's going to take up 2 clusters or 32K of storage space on your hard drive. Now if you increase the size of the drive, and each cluster now contains 64 sectors… You can see how this makes for a lot of wasted space on the HD. A single partitioned hard drive can waste up to 40% of its storage space, depending on the average size of the files stored there.

When 1Gig and 2Gig hard drives first came out, the way to get around this wasted space was to partition the drive into 2 or more logical drives. Each logical drive has it's own FAT which reduces the required number of sectors in each cluster, resulting in less wasted space. With Windows95 (SR-2) and Windows98, the 32-bit FAT was introduced which increases the number of clusters that can be mapped. For drives up to 8Gig, cluster size is only 4K, and the increases seem less dramatic after that (for now).

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