STORAGE – HARD DRIVES AND FLOPPIES
Floppy Drives
In the study of a hard drive the first place to look is at floppy drive technology. Even though floppy drives are old and obsolete they are still around in a few computers and there is a relationship between a floppy and a hard drive. Looking back at older computers you may remember having an A drive and a B drive. A drive was in some cases the boot drive and required a disk to boot; however, that is going way back. A drive was a 3.5" drive and held 1.44 MB of storage. Both A & B hooked to the motherboard via a data cable with a 34 pin connector. On these older computers both A & B were connected by the same data cable; however, newer computers will only have one cable and just the 3.5 floppy drive. Drive B was a 5.25" floppy and since they were both hooked to the motherboard by the same data cable, the distinction of these two floppies was made by the BIOS. The 5.25" drive has gone the way of the Dinosaurs and is no longer available on most computers. The cable used was identifiable by a twist in the cable for drive A and number 1 pin had a color along the edge of the cable.
In preparing the floppy for use you need to know a little about its construction. Inside that disk is a flat, blank, magnetically coated plastic cylinder with nothing on it. There are no groves, no sectors, and no writing. In order to use this cylinder we must prepare it or make it ready to accept data by a process called formatting. The first thing done is to format the disk by inserting it into the proper drive, going to the DOS prompt (A ://>) and typing the command in the line telling the computer to prepare this disk for use. When you hit enter it will begin its work of creating circles or tracks and sections called sectors on the disk. When it is finished a high density disk will have 80 circles or tracks on each side of the disk and 18 sectors on each side and the circles will be numbered 0 through 79 and the sectors numbered 0 through 18. All sectors will store the same amount of data. The data is written to the disk in binary code of 1's and 0's with each bit being magnetized. I normally do formatting from the dos prompt but you can also format from a shortcut in Windows Explorer. All material is written using magnetism for the binary code 1's and 0's and a different magnetic code for the spaces. When it is read the computer uses a magnetic read/write head mechanism in the floppy drive. There is some difference in the method used by a floppy drive as opposed to a hard drive. The floppy drive head lightly touch the surface of the disk while the disk is rotating at 360 revolutions per minute. The floppy drive has two heads, one on top of the cylinder and one beneath and they move back and forth in unison. A hard drive works the same way but the drive heads never touch the disk.
Let's dig a little deeper in this hole of knowledge. Sectors can be grouped as one or more sectors together making up a cluster. A cluster is the smallest unit of space on a disk used for storage and just like your office at home you need a filing system to keep everything organized. On your computer that filing system is a "FAT" or File Allocation Table and on some newer units it will be a NTFS or New Technology File System used on Windows NT, 2000, and XP. NTFS provided better security and more storage than FATs.
Now that we have a File Allocation System we need some explanations about the system. The first sector in the file cabinet is the boot record and it tells us how many sectors the disk has and how many sectors are allocated per cluster and how many bits are in each FAT entry. It will also advise of the version of DOS or Windows used in the formatting process of the disk.
If your floppy drive has a problem the idea now is to replace it because the price has made repairing of floppy drives obsolete. I am not going to go into detail here on replacing the floppy. It is very simple and directions for your computer can be found on the internet in Google. One word of caution, if you do decide to replace a defective floppy don't forget about electro static discharge (ESD) and make sure you are properly grounded before entering the case. In the beginning of this discussion I stated the floppy drive and hard drive were similar. In fact they are very similar. Where a floppy has one Mylar disk a hard drive will have two and possibly more.
HARD DRIVE
Let me emphasize hard drives are fragile and should be handled gently. If you listen to your hard drive as it spins up and hear crunching or unusual sounds, prepare to install a new hard drive. The platters or disk spin in unison and all that I have seen were housed in a metal case. Inside this case are firmware chips and devices to read and write information to the platters or disks. Just like floppies the key to a hard drive is magnetism. Material is written to the platters by a magnetic spot and this is one reason nothing with magnetism should ever get close to your hard drive or for that matter the computer. Magnetism can totally destroy the data on a hard drive in microseconds. Another similarity to a floppy is if you have multiple platters data is written to both sides. Similar to a floppy data is written to the platter beginning from the outside of the circle and continuing to the inside and even though it would seem the sectors are smaller they all contain the same amount of data. This does not hold true with newer units because a new technology was introduced called zone bit recording. Even though it differs from the older drives each sector still holds 512 bits of information. Just like the floppy, hard drives are disposable and when sectors begin to fade or go bad, pull the drive out and replace with a new one. Just be sure to try and recover as much of your data as possible. Hard drives eventually fail and will begin rendering "Bad Sector or Sector Not Found" errors and this is usually caused by fading of the low-level formatting done by the factory whereby it set track and sector markings. As the computer ages these lines gradually fade to the point of eventual failure errors. They have a life expectancy of, "the life of the drive."
Older computers built during the first 1990 years were rather primitive and their controllers couldn't handle complicated arrangements that changed between tracks. As a result, every track had the same number of sectors. This wasted a great deal of space but since all sectors held the same number of bytes, it was easy to calculate the size of the hard drive. If you knew how many tracks, heads, and sectors were on the hard drive you could simply multiply the number of heads, by tracks, by sectors, by 512 bytes and this gave you the size of the hard drive. An example is (855 X 7 X 17 X 512.) then you must divide by 1024 and divide again by 1024 to convert to MB and this gives the size of the drive. I remember my first 25 MB computer and at that time in 1993 it was state of the art. Today it would not have enough memory to install even the smallest available PC operating system.
