CIS 1110A - Computer Operating Systems and Maintenance


Module 5

This lesson discusses hard drives and other data storage devices. Objectives important to this lesson:

  1. How a hard drive works
  2. How a computer uses a hard drive
  3. Choosing and installing a hard drive
  4. Optical,solid state, and flash drives
  5. Troubleshooting
  6. Current assignments

Concepts:

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.

    floppy disks

  • 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 the drives.)

    Historical Hard Drives

    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.

    • Yellow Track
    • Blue sector
    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 type. .

    (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 representation.)

  • 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 features:

  • 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 Windows:

  1. Install the new hardware
  2. Tell the BIOS/UEFI about the new hardware
  3. Start Windows, and let it assign a drive letter/pointer/volume label to the device (The usual label for the first hard drive is C:)
  4. 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 performance expectations.

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.



Assignments

  1. Read the chapter, and the next one for next week.
  2. Complete the assignments and class discussion made in this module, which are due by 6pm next week.