CPS100 • Introduction to Computers

Lakeland College • Japan Campus


As explained previously, "storage" is a general term for the keeping of data in a more permanent way (non-volatile). Any device which can remember data even when not receiving power is called "storage."

Most storage is used in "drives." A drive is a device that records and reads data on a storage medium. The part of the device which keeps the data can be called media. Many drives use removable media, meaning that you can remove one disk and put in another.

Floppy Disks

We'll begin with a legacy type of storage: floppy disks. "Floppy" means limp, loose, and bendable. This may confuse younger people because the floppy disks most people know are made of hard plastic which does not bend well.

There were three widely used types of floppy disks: 8-inch, 5.25-inch, and 3.5-inch. All three used flexible circular mylar sheets which could hold magnetic information (thus the name "floppy").

Description Description

The8-inch (20 cm) disks were released in the early 1970's and could only hold about 80 KB of data at first. Later versions could hold more than a megabyte. However, these disks were very large and clumsy.

The 5.25-inch (13 cm) floppy is more well-known, as it was introduced with the first popular personal computers in 1977. At first it had capacities of about 160 KB, but later 360 KB, 720 KB, and even 1.2 MB versions were released.

Finally, the 3.5-inch floppy was released in the early 1980's, but became popular only when the first Macintosh computer was released in 1984. It was the first floppy which could fit in your pocket, and which had a hard plastic case. At first it had capacities of 400 KB and 800 KB, but was best-known for the "HD" version which could hold 1.44 MB.

Floppy disks began to disappear in 1998 when Apple introduced the iMac, one of the first popular computers without a floppy drive. Floppies remained common on Windows PCs for many years afterwards.

Optical Discs

Optical discs (not "disks") are hard plastic discs which store data when a laser beam burns microscopic holes on a layer inside the plastic. Thus, we say that we burn a disc when we record data on it.

There are three basic types of optical media: ROM (read-only memory), which is made with data printed on it and can only be played; R (recordable), which is blank and can only be burned once; and RW (rewritable), which is blank and can be recorded, erased, and re-recorded on many times.

layers on an optical disc

Most optical discs today are single-sided, but many also have multiple layers of data. For example, there is a DVD type called DVD-R DL (DVD-Recordable Dual-Layer) which has two layers. Blu-ray discs come in 1-layer, 2-layer, and 4-layer types. Adding layers adds capacity.

Lineup of optical disc types

The first generation of optical discs were Laserdiscs, giant 30-cm discs released in 1978 and used mostly for movies. Even when double-sided, some movies required two discs (3 sides), and the movie would have to pause while you removed the disc and flipped it or replaced it. These discs were never used in personal computers.

in 1982, Compact Discs (CDs) were released as a new music media, to replace vinyl records and cassette tapes. At 12 cm, they were a much more reasonable size than their Laserdisc cousins. They have a capacity of 700 MB. They were not used for data storage on personal computers until the late 1980's.

In the mid-1990's, DVDs (Digital Versatile Disc, Digital Video Disc) were released. Just as CDs were designed for music, DVDs were initially intended for movies. However, they were picked up for use in personal computers by 1997. There are many types of DVD, but the most common type can hold up to 4.7 GB of data.

When popular video was making the switch to HDTV, it was clear that DVDs could not hold enough data to save a movie in Full HD resolution. A new disc type was needed. In 2006, Blu-Ray was released, able to hold 25 GB, 50 GB, or even 100 GB on a disc. This was quickly adopted for computers, and many Windows computers today come with built-in Blu-ray drives. Blu-ray discs can save more data because they use a higher-frequency laser, thus the "blu" in the name.

Apple never adopted Blu-ray, and has even begun to drop optical drives from several of its computer models. While optical discs are cheap and can last a long time, they are slow and difficult to use. Today, they are used less for storage, being replaced by USB flash drives and cloud storage.

Name Released Capacity Used for: Bigger than:
CD 1982 700 MB Music, data 1 CD = 500 floppy disks
DVD Late 90's 4.7 GB + Video, data 1 DVD = @ 7 CDs
Blu-ray 2006 25 GB + Video, data 1 Blu-ray = @ 5 DVDs

Type Read-only Recordable Re-Writable

HDD (Hard Disk Drive)

When PCs were first introduced in the late 1970's, HDDs were incredibly expensive, so only floppy drives were used. A decade later, by the end of the 1980's, HDDs had dropped in price so that most PCs had an internal hard drive. Today, most computers still have hard drives, but they are beginning to disappear, being replaced by SSDs.

The advantage of HDDs is that they are cheap and can hold huge amounts of data. HDD capacities from 1 TB to 3 TB are common. 1 TB HDDs begin at about $50, or 20 GB for $1. Hard drives are also fairly reliable.

However, HDDs are also very slow, as they are not solid-state. The metal disks inside spin at speeds such as 120 times per second. To save energy, they stop spinning when they are not being used. It takes time to spin up and spin down. Furthermore, metal arms must move back and forth across the disks to read and write data, causing further delays. Finally, HDDs tends to be heavy, are noisy, and are too large and bulky for slimmer computer designs.


Flash memory is a type of solid-state chip which is non-volatile, and thus falls under the category of storage. It is fast, small, and reliable, and recently has become fairly cheap. You can buy a 32 GB USB flash drive for ¥1850, which comes out to about 1.7 GB for $1. That is more than 10 times more expensive than HDD storage, but the size and convenience of flash drives makes them highly popular.

Flash storage became widely used because of iPods, iPhones, iPads, and digital cameras. All are extremely popular and all use flash memory. Huge orders for flash memory for these devices has drive the cost of flash storage down to remarkably lower prices than before.

The first iPods actually used very small HDDs, but these were very inconvenient. HDDs have moving parts, and if you shake an HDD during use, it can damage the disk. The HDDs in iPods used to stop spinning whenever there was too much movement. However, since many people like to listen to music while jogging or exercising, this became a significant problem. Soon, iPods began to switch to flash memory, beginning with the smaller iPod Nano.

Flash storage does have a disadvantage aside from price: it wears out. After perhaps 10,000 write-and-erase cycles, a memory cell in flash can go bad. However, newer flash drives have the ability to detect and avoid damaged cells (called "wear leveling"), and will simply avoid using them. Thus, it is possible to use a flash drive millions of times before it stops working.

In addition to USB drives, flash memory has many card forms. The most popular seems to be SD cards. Also used are Micro SD, Compact Flash (CF), Memory Stick, and others. Many computers, printers, and other devices have built-in flash card readers.


SSD (Solid State Drive)

SSDs are an emerging technology. They are based on the same flash chips used in USB flash drives.

The SSD is beginning to replace the HDD. Despite still being very expensive, SSDs have two major advantages. First, they are fast. If your computer has an SSD, it will probably boot up twice as fast as a similar computer with an HDD. Second, SSDs are small and can be made into almost any shape; this is required for new ultra-slim computers.

Currently, SSD drives cost about the same per gigabyte as USB flash media, about 1.7 GB per $1. This makes them significantly more expensive than HDDs for computers. However, because SSDs are much faster and allow for super-slim notebook designs, they are becoming more and more popular despite the price.

There is a way to have both the speed of an SSD and the capacity of an HDD, using a technique called SSD caching (Apple calls it a "fusion" drive). Both an SSD and an HDD are used together, but commonly-used data is stored on the SSD, while less-used data is stored on the HDD.


Historically, prices for storage have dropped, sometimes very quickly. I remember buying a HDD in the early 1990's; it cost $300 for a 105 MB drive, almost $3 per megabyte. You may recall that today, HDDs cost about $1 per 20 GB—about 60,000 times cheaper over 20 years!

Similarly, I can recall USB flash memory at much higher prices. For example, about ten years ago, a 128 MB USB flash could cost $30, or about $240 per gigabyte. Today, a 32 GB drive costs about $20, about $0.60 per gigabyte—about 400 times cheaper.

However, prices have been stalled over the past few years. In 2011, there were massive floods in Thailand, where many HDD factories were located; the prices of HDDs went up, and are only just now beginning to drop below 2011 levels.

Strangely, for the past 1 year, flash memory prices have stayed about the same, and SSDs have actually increased a little.

The Cloud

A new form of storage is becoming popular: the Cloud. Cloud storage is remote storage, accessed over an Internet connection. A company has a data farm (or "data center"), a building filled with HDDs connected to high-speed web servers. The company allows users to save whatever data they like using the facility.

Cloud storage has become popular especially due to mobile devices, or the fact that one person may have multiple devices. For example, I have a desktop computer, a laptop, a tablet, and a smartphone. It is difficult to keep the same data up-to-date on all my devices. However, if I keep my data on a cloud, all my devices can access the same data, and therefore keep in sync.

A calendar synced over the cloud

The disadvantage of the cloud is obvious: speed. Even with a fast Internet connection, it is much slower to access data over the Internet than it is to get it from a drive connected to your computer.

The advantages of using cloud storage are significant, however. Besides syncing data on all of your devices, cloud storage allows you to access data from any computer connected to the Internet. It is also more secure, as data centers regularly back up data, and data losses are rare.

Currently, many companies offer large amounts of free cloud storage. Apple offers iCloud accounts with 5 GB free storage. Google, however, offers its GMail users up to 30 GB of free cloud storage, and does not limit the number of accounts you can use. Flickr recently increased free cloud storage of photos to 1 terabyte.

Terms to Know

storagethe keeping of data in a permanent way on non-volatile media.
drivea device which reads and writes data on a storage medium.
mediaa specific form of storage, e.g. a CD, floppy, or HDD; plural of "medium."
removable mediastorage media which can be removed from the drive; HDDs and SSDs are not removable media.
floppy disksan outdated storage medium with capacity limited to 1.4 MB at largest.
optical storagestorage where data is saved on a plastic disc using a laser.
burnto record on an optical disc.
CD, DVD, Blu-Raycurrent optical media, with standard capacities of 700 MB, 4.7 GB, and 25 GB respectively.
-ROM, -R, -RWread-only, recordable, and re-writable, respectively (on Blu-rays, it is -ROM, -R, and -RE).
layerssome optical media allow for two or more layers of data, thus increasing capacity.
HDDhard disk drive, a magnetic, non-volatile, non-solid-state, non-removable storage media.
flasha non-volatile solid-state media.
SSDSolid State Drive; a form of flash storage used in place of HDDs.
SSD cachingusing HDDs and SSDs in combination to achieve fast speeds and high capacities.
the cloudInternet-accessed remote storage.
data farma facility with massive numbers of storage devices, able to keep great amounts of data, often for cloud services.
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