One of the most popular interfaces used in the notebook PC world is the PC Card
interface, also sometimes called PCMCIA after the group that created it in the
late 1980s. This interface standard was created to allow for easier expansion of notebook
systems, which at that time had very few options for adding hardware at all. For
information on the PC Card interface as it relates to hard disks, see this page.
Despite the relatively small size of cards that adhere to the PC Card standard, hard
disk engineers have managed to create hard disks to fit. There are actually three PC Card
form factor sizes, defined by the PCMCIA in 1995. The width and depth of these devices is
exactly the same as that of a credit card, which I am sure is not a coincidence! They are
all 2.13" wide and 3.37" deep. The three sizes differ only in their height. Type
I devices are 3.3 mm thick; Type II devices are 5.0 mm thick, and Type III devices are
10.5 mm thick. Originally, the intention was for solid state devices like memory, modems
and the like to use the Type I and Type II devices, while the Type III devices were for
hard disks. Due to the extreme height limits of PC Cards, it is difficult to make hard
disks that will fit into the allowed space, and most PC Card hard disks are Type III.
However, advances in miniaturization have allowed some companies to now make hard disks
that actually fit into the Type II PC Card form factor as well. Since most laptops can
only accept either two Type I/II cards or a single Type III, this is a
significant advantage. Here's a summary table of the different sizes:
Form
Factor |
Width
(in) |
Depth
(in) |
Height
(in/mm) |
Application |
PC Card
Type I |
2.13 |
3.37 |
0.13 / 3.3 |
Not used for hard disks
(yet?) |
PC Card
Type II |
2.13 |
3.37 |
0.20 / 5.0 |
Smaller-capacity expansion
hard disks for laptops and consumer electronics |
PC Card
Type III |
2.13 |
3.37 |
0.41 / 10.5 |
Higher-capacity expansion hard
disks for laptops |
The 2.13" width of this form factor puts a hard limit on the platter size of these drives--even 2.5" platters are too
large. Most PC Card drives today use 1.8" platters. Interestingly, the first hard
drive to use the PC Card form factor was probably the Hewlett Packard Kittyhawk
drive, with much smaller 1.3" platters. This drive is a good example of a technology
being "ahead of its time". It was actually introduced way back in 1992, very
early on for such miniaturized technology. Unfortunately, at the time the market may not
have been big enough to provide HP with sufficient revenues to keep making it. The
Kittyhawk was used in early hand-helds and other small consumer electronic devices (even
printers!) for a while, but was eventually discontinued, and HP is no longer making hard
disk drives of any sort. If this technology had been introduced five years later, it may
have been a runaway success; certainly IBM is having great success with its
slightly-smaller Microdrive.
|
A CompactFlash card (left) and a PC Card (right).
The quarter is included for size context. Neither of
these is a hard disk (though the SanDisk is a solid-
state flash card "hard disk") but are the same size and
shape as hard drives of their respective form factor. |
Note: Many companies also
make "solid state drives" using the PC Card form factor. These perform the same
function as hard disk drives, but are not hard disks at all: they are actually flash
memory, a type of ROM. I discuss this in more detail
in the section on the CompactFlash form factor.
Interestingly, with a couple of exceptions, most of the smaller PC Card hard disks are
not made by the bigger, well-known hard disk companies, but rather smaller niche
companies. I am not sure what the reason is for this. I suspect that there just may not be
enough profit potential there for the big names to bother with this market, which is small
compared to the market for mainstream PC drives.
Next: CompactFlash
Form Factor
