Whether it be hard disk or floppy disk drives, the size of the drive, it's form factor, is determined by where it will be
installed, the drive bay of a computer or rack enclosure. Commonly used disk formats come from historic pseudo-standards
arbitrarily introduced by single manufacturers and were later formally standardized in industry wide standards. Form-factors
are named by their
width. Note that this name-giving width isn't the actual outder dimension but the size of the
internal platter, magnetic disk or removable diskette. Some form factors seem to follow a nestable scheme, where one larger
form factor would hold multiple instances of the next smaller form factor, similar to how ISO
paper sizes
are multiples in size of the next smaller sized sheet. But that's more an impression and only true for full-height /
half-height versions of a respective form-factor.
8.0-Inch
H/W/D: 4.624 in × 9.5 in × 14.25 in (117.5 mm × 241.3 mm × 362 mm)
4+5⁄8 inches (117.5 mm) high, 9+1⁄2 inches (241.3 mm) wide, and approximately 14+1⁄4 inches (361.9 mm) deep
The 8.0" drive and drive bay format was introduced by IBM and Tandy. When third-party manufacturers began to offer form-factor
and interface compatible drives, hard-disk-drives and floppy-disk-drives, the format began to "stick". (Actually the same happened
for the drive interface, the
ST-506 / ST-412 interface.) Shugart Associates,
which after a Xerox buyout returned as Shugart Technology and ultimately became Seagate Technology, adopted the format with the SA1000
model and offered later compatible drives like the ST506. Micropolis as well offered early rigid disk drives in this format,
drives from the
1220 and
1240 series.
5.25-Inch
Full-height:
H/W/D: 3.25 in × 5.75 in × 8 in (82.55 mm × 146.1 mm × 203 mm)
3+1⁄4 inches (82.6 mm) high, 5+3⁄4 inches (146.1 mm) wide, and up to 8 inches (203.2 mm) deep
This drive bay format is named after the size of a
5.25-inch floppy-disk that
would fit in a floppy-disk-drive made for such drive bays. The actual bay is 5.75-inches (146.1 mm) wide and the front opening
even 5.875-inches (149.2 mm) wide. By coincidence, this drive bay is more or less 8 inches deep, resembling the next larger
form-factor. Note that these dimensions are the
full-height drive dimensions (abbreviated as "FH", or "FHT"), which were used until mid 1980.
Micropolis manufactured a number of full-height 5.25-inch hard-disk-drives. In our
HDD support section
they are tagged with the "FHT" abbreviation. Sometimes you might find "FHHL" (full height, half length) devices.
Half-height:
H/W/D: 3.25 in × 5.75 in × 8 in (41.3 mm × 146.1 mm × 203.2 mm)
1+5⁄8 inches (41.3 mm) high by 5+3⁄4 inches (146.1 mm) wide, and up to 8 inches (203.2 mm) deep
Half-height (abbreviated as "HH", or "HHT") is, just as the name implies, a 5.25-inch drive bay utilized only half, so that two half-height devices can
usually fit in one full-height bay. Half-height used to be the standard housing dimensions for more modern 5.25-inch floppy disk
drives and "slimline" or "low-profile" hard-disk-drives of the late 1980s. Today, CD and DVD drives usually follow this form-factor
in width, but come in even shallower height factors, which in turn are then called slimline optical drives. In addition to Half Height, there's also
HHHL (half height, half length) and sometimes "SL" or "1/3HT", for slimmer drives than half-height. You can find many of these
abbreviations for drive-bay form-factors on the
Micropolis Hard Disk Drive Support pages.
3.5-Inch
H/W/D: 1.028 in × 4 in × 5.75 in (26.1 mm × 101.6 mm × 146 mm)
1.028 inches (26.1 mm) high, 4 inches (101.6 mm) wide, and up to 5.75 inches (146 mm) deep
3.5 inch drive form factor used to have a "full-height" version as well and manufacturer Rodime offered a 3.5 inch full-height
hard-drive in the early 1980s, but most drives, floppy and rigid disk, usually use the 3.5 inch half-height format which is 1 inch
high. While full-height drives were still common with HDDs during the 1990s, today the "low profile" 3.5-inch form-factor is the
most common one for 3.5-inch floppy disk drives and hard-drives - with hard-disks slowly fading towards 2.5-inch or smaller form
factors with solid-state memory.
Micropolis manufactured a number of drives fitting the 3.5-inch form-factor, in full height for example the large-capacity
Tomahawk drives from the
3391 series but also in half-height, like the
Micropolis Aries 2
or
lower capacity Tomahawks.
Note on abbeviations
Above, H/W/D means "Height, Width, Depth". In Micropolis technical documentation you may also find the L/W/H abbreviation for
"Length, Width, Height" which is more common in engineering, while H/W/D is more common in sales/product descriptions.
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