CIS 1110A - Computer Operating Systems and Maintenance
This lesson discusses hard drives and other data storage
devices. Objectives important to this lesson:
How a hard drive works
How a computer uses a hard drive
Choosing and installing a hard drive
Optical,solid state, and flash drives
The chapter opens with a description of hard drives. First, a
little history. A long time ago, in a galaxy far away... there
were hard disks and floppy disks.
Floppy disks were portable mylar disks,
typically in plastic jackets, that were coated with iron or
cobalt oxide. They had to be loaded into floppy drives to be
read (rhymes with red) or written to by a computer. In the image
below, the disk in the black jacket is 8 inches in diameter.
Those were used for a while in systems like Lannier word
processors. The disk with the orange/coral jacket is a 5.25 inch
disk. The blue disk on the right has a hard jacket with a
shutter. It is a 3.5 inch disk. 3.5 inch disks were sturdier
than the other two sizes, but they were still called floppies.
Only the 5.25 and the 3.5 inch sizes were used much in personal
computers. (There is a lot more to it than this, but that's
enough for the moment. Want more? Click the picture.) Without
their jackets, floppy disks were not useful. A thin plastic disk
is just floppy, vulnerable, and unuseful.
Hard disks are the actual metal platters,
usually made of aluminum, mounted on a spindle inside a hard
drive, which is the actual storage device. Metal
disks can be spun faster than thin plastic disks, so data access
is faster on hard drives. The text mentions that common spin
rates for hard drives are 5400, 7200,
10,000, and 15,000 RPM (revolutions per minute). The two rates
show in bold are the most common for personal computers.
Hard drives have come in a lot of sizes, some of which are shown
in the open drive cases below. (By the way, opening the cases ruins
In the image above, you may think you see transparent disks in
the open hard drives in the foreground. What you really see are
very shiny disks that are reflecting the
table and the objects around them. Note that the visible disk in
the large drive in the background is no
longer shiny. It has been oxidized by
contact with air, making the disk useless. The others will be
useless soon, Don't open a hard drive! They are vacuum sealed
for a reason.
Floppy and hard drives save data on their disks with magnetic
read/write heads, similar to way tape recorders work. Data on
disks is arranged in tracks and sectors.
The yellow circle in the image on the right represents one
track on a disk, the one closest to the outer edge.
One sector in another track is shown in blue.
Sectors are numbered units of storage in which data can be read
or written. The number of sectors on a disk varies from type to
(In the picture on the right, the number of sectors per track
and the number of tracks have been reduced to make the image
clearer. The picture is a metaphor, not an exact
The text mentions that desktops commonly use 3.5 inch wide
hard drives, and laptops often use 2.5 inch wide drives
A hard drive must have one read/write head for each side of
each platter (actual disk) in the drive. The heads are
mounted on an actuator, which is a mechanical
arm that moves across the disk like the arm on a record
turntable. (If you have never owned one, and have never seen
one, go see a movie! Here is an illustration
on Wikipedia.) The heads actually fly just above (and below) the
platters like hovercraft. If a head were to hit a hair or a dust
particle at the rotational speeds listed above (imagine being on
the disk, speeding toward the head...) there would be an actual
crash as the head hit the media surface. This is why hard
drives are sealed air-tight: to avoid dust, hair, etc.
entering the drive.
Solid state drives (SSDs) are becoming common
options. They do not use disks. Instead, they use non-volatile
memory to hold data. The text explains that the type of memory
used is called NAND, which stands for the logic term "Not AND".
This make little sense in the context of the chapter, so I will
refer you to a quick lesson in computer logic that I wrote for
another class: https://stevevincent.info/CS231_2015_8.htm
There is a saying about hard drives that is a warning to computer
users: all hard drives die. They eventually wear
out. The text expands on this warning, telling us that all
SSDs die. No, they are not magic. They will eventually
fail when enough data write operations cause
their transistors to go bad. A rule of thumb from our author is to
assume there is a reason that SSDs only have five year warranties.
In 2020, you may see three major kinds of SSDs::
2.5 inch case-mounted devices that fit into 2.5 inch hard
drive bays; these typically use SATA connections which means
they can't transfer data faster than a SATA HDD
M.2 drives that fit into M.2 motherboard slots, and on
M.2/PCIe slot adapter cards; these typically have faster NVMe
data interfaces (see below), but some do not. Some cards only
access the SATA interface through the M.2 slot
PCIe cards with built-in SSD cards
When SSDs are placed on PCIe cards, whether by the manufacturer
or by the user, the SSDs and the
cards should use an NVMe (Non-Volatile Memory Express) interface
through the PCIe slot. This is explained in the video below. Not
all SSDs use NVMe, so buy carefully.
The text turns to a discussion of hard drive interfaces, which
includes some of the facts above.
IDE - The author discusses only one type of
ATA interface, the Parallel Advanced
Technology Attachment (parallel meant that data passed through
multiple lines simultaneously) version called Integrated
Device Electronics (IDE), which meant that the
necessary controller card for the drive was attached to the
drive. These drives were a standard several years. The text
explains that early IDE drives used 40 conductor cables, and
later drives used 80 conductor cables. Both of these cables were
parallel ATA (PATA) cables. An 80 conductor cable
actually had 40 pins, just like the 40 conductor cables. The
other 40 wires were grounds to reduce crosstalk (signal
crossover) from the other data wires. The grey ribbon cable
shown in the image on the right is an IDE cable. It would have
had a connector for the motherboard on one end, a connector for
a drive on the other, and often it had a connector for a second
drive near the middle of the cable. (You hoped the two drives
were mounted close to each other in the case.)
SCSI - Small Computer System
Interface drives were never very popular, but they
were interesting. The text explains that SCSI was called a bus,
and that you would typically attach one device to a SCSI
controller card, then run a cable from that device to the next
device you are putting on the bus, and so on up to a limit
dictated by the card you were using. The first time I used this
interface was to install a SCSI card in my computer so I could
use it with a flatbed scanner. The text explains that this
interface is no longer included in personal computers.
SATA - Serial ATA interface
is a common interface for hard drives and other devices. The
red/orange cable shown in the image on the right is a 7 pin SATA
data cable. The text mentions three data bandwidths available on
three versions of SATA:
SATA 1 - 1.5 Gbps
SATA 2 - 3 Gbps
SATA 3 - 6 Gbps
The text wants you to know that SATA data cables typically
have 7 pins, and SATA power cables have 15 pins
SATA 3.2 allows SATA devices to work with PCIe to triple the
bandwidth of SATA 3, and using wider connectors; this is not
seen much since data passed through NVMe flows faster
eSATA is a standard for connecting an external device to a
computer's SATA bus. It uses a different connector.
NVMe - we discussed this in the notes above,
but the text has more details. This video addresses classic
M.2/SATA and M.2/NVMe
The text discusses choosing between the varieties of hard drives
and installing them safely. This section goes on through page 240,
and you should browse through it carefully the first several times
you try to do each variation. Here are some notes on considering
capacity - how much space do you want? All things being equal
(which they are not) bigger drives cost more.
rotational speed - how fast does it spin? Faster drives are
often faster at accessing data, but they are also typically
noisier, hotter, and more expensive. Typical speeds currently
available are 5400 rpm and 7200 rpm drives.
technology used - This refers to the list above. The lower in
the list, the newer and more expensive the technology, which
often means better performance. However, make sure that the
technology you want will work with your motherboard.
cache size - the bigger the cache the better the drive, and
the more costly
average seek time - in other words, on average, how long does
it take the drive just to find the data you ask for? Smaller
numbers are better
On page 241, the text discusses another A+ objective: file
systems used by storage devices. Most hard drives (and floppy
disks, for that matter) require several steps to make them ready
to use the file system used by the other devices in your computer.
RAID file systems are challenging, but most users never need that
complication. This is a short version of what to do, based on
Install the new hardware
Tell the BIOS/UEFI about the new hardware
Start Windows, and let it assign a drive letter/pointer/volume
label to the device (The usual label for the first hard drive is
Format the drive in File Explorer. When doing this, consult
the list of file systems at the bottom of page 241.
Optical discs (yes, it is spelled that way for
optical media) is a storage category that includes CDs (Compact
Discs), DVDs (Digital Video Discs), and BDs
(Blu-ray discs). There is a chart on page 243 showing
the growth of storage capacity across various disc versions.
Optical drives are confusing without a chart to
make sure you are not ignoring important details. The author
suggests that you study the chart on pages 244 and 245. Pretend
you are advising a friend about which product to buy, based on
The chapter continues with a section on replacing internal
optical drives, but it is only about a page long. It goes on to
discuss flash memory and Secure
Digital (SD) cards. A table of SD cards appears on
page 249, but they are not shown at the same scale. The
soft-spoken presenter in the next video makes the form factors,
speed ratings, and misleading product claims clear.
Read the chapter, and the next one for next week.
Complete the assignments and class discussion made in
this module, which are due by 6pm next week.