About the Midterm
Midterm 1 will be Monday, October 7th. It will be held in the SB Union Auditorium to ensure enough space for everyone to be comfortable.
The test will cover all the material we have had in lecture prior to the midterm, covered by Chapters 1 to 6 of Shelly-Cashman-Waggoner. Reading the text to augment the on-line lecture notes is a good idea.
The level of the questions is likely to be at that of the short answer questions in the text. To study, I urge you to work through the ``What you should know'' and ``Test your knowledge'' sections of the book, as well as reviewing To study, I urge you to work through the ``What you should know'' and ``Test your knowledge'' sections of the book, as well as reviewing the lecture notes.
I will have an optional question/answer review session after class in the CS Seminar Room.
Secondary Storage Devices
Secondary storage devices serve the same role as a library does for reading. There is only room for one book at a time on our reading table (main memory), so we take out what we need.
The most important secondary storage devices are:
Floppy disks
Floppy disks used to be floppy - now they are encased in a hard shell, but inside the magnetic material is still flexible.
Magnets have north and south poles. All magnetic media work by controling the orientation of the magnetic field. North/south = 0/1.
Standard 3.5 inch diskettes hold 1.4 megabytes each, although even higher densities are possible.
Achieving higher densities requires both more sophisticated floppy disk drives with better magnetic heads, and also better quality ("double density") diskettes with the magnetic bits closer together.
Floppy disks are very fragile things - take care of them!
Formatting
Disks simply store patterns of bits, which can be accessed only by giving the appropriate address.
We seek to access what is on the disk by their file names. To do this, there must be a place on the disk which for each file name records where on the disk it is.
Setting up an initial file directory, and other disk organization information must be done by software. This process of organizing the raw bits is called formatting.
Making sense of the data on the disk requires the "disk controller software" to understand the specific disk format used. This is one reason why IBM PCs cannot easily read Apple diskettes and visa versa.
Hard Disks
Hard disks are much faster than floppy disks because they revolve around so much faster, say 3600-7200 revolutions per minute, vs. about 360 rpm.
Because hard disks are not removed and transported the way floppies are, there do not have to be a standard size. Each company tried for the biggest capacity they can get instead of having to satisfy a standard.
Hard disks for PCs have capacities up to about 4 megabytes, but even larger sizes exist on mainframes and supercomputers.
The disk head flies amazingly close over the surface of the disk, while the floppy disk head scrape the disk.
The time to get data from a spinning disk is a combination of seek time (how long does it take the head to get to the right track), latency time (how long does it take for the data to rotate under the head), and read time (how fast can we grab data as it rotates under us).
CD-ROMS
CD-ROMs are an optical, not magnetic media, with a capacity of 650MBs.
Bits are written on the disk using a laser, which etches a mark which does not reflect light for a 1.
CD-ROMs are write once, read many times, sometimes called WORM media. How useful would a WOM be?
CD-ROMs are read by shining a laser on the disk, and seeing if the light is reflected or not.
CD-ROM drives are sold according to speed.
Thus a 
drive is four times faster than the original slow media.
Magnetic Tapes
The highest capacity media are magnetic tapes, which usually used to backup or archive data.
Backup is a critical problem, especially for home and small business computers, because people usually keep the backups current. Then the disk crash comes.
Tapes are sequential access media, unlike disks, which is one reason they are so slow. To get a file at the end of the tape, you must scan through the entire tape!