Accessing Data

The process of accessing data has 4 steps. 1.  Seek _[32] 2.  Rotate 3.  Settle _[33] 4.  Data transfer

Step	Measured as:	Click to start and stop animations
1. seek move the head to proper[34] track	seek time (ms)
2. rotate rotate disk under the head to the correct sector	rotational delay (ms)
3. settle head lowers to disk; wait for vibrations from moving to stop (actually touches only on floppies)	settling time (ms)
4. data transfer    copy data to main memory	data transfer rate (kbs)

where ms stands for millisecond = .001 second and kbs is kilobytes per second.   Total time to transfer a kilobyte:

for floppies,	175 - 300 ms
for hard drive,	15 - 80 ms
new hard drives,           (Jan. 2000)	.0146 ms   (66.6 MB per sec). This is seriously fast!!

Clearly, getting data from a hard disk is immensely faster than from a floppy.

Caring for Data

Besides protecting the physical medium you are using to store data, you must also consider what you can do to safeguard the data itself. If the disk is kept from physical harm, but the data gets erased, you still have a major problem.   So what can you do to safeguard the data on which you rely??

Write protect	This keeps your files from being overwritten with new ones. For floppies, you do this physically:
	5¼" = cover the Write Protect notch[35] with tape
	3½" = open the Write Protect slide

For hard disks, make files Read-Only and/or Hidden to keep them from being overwritten. This is done by changing the file attributes using whatever system you have for managing files. This is useful only for files you won't be altering_[36] later.

Backup

Make multiple copies of important data often. The more important the files are, the more copies in more places you need.

Antivirus

Use an antivirus program continuously_[37]. Computer viruses are sneaky_[38] computer programs that can erase your data and even your whole system. Most viruses are merely_[39] annoying and are created as practical jokes. But there are a number of very damaging viruses out there.

Your computer gets a virus by downloading an infected file from the internet or your office network, or by first using a floppy in an infected computer and then accessing a file on that floppy with your own computer. This makes it difficult to keep a virus from spreading_[40].

Once you have disinfected your computer, it can get re-infected from a floppy that was used between the time you were infected with the virus and when you disinfected it. A number of nasty_[41] viruses hide for quite a while before doing their nasty things. So you can infect a lot of your own backups and other disks and spread the infection, all unknowingly_[42], to others. So run an antivirus program that actively looks for viruses all the time. Don't wait until you have symptoms. A lot of damage can be done before you figure out that you have a virus.