Wednesday, November 14, 2007

Hard disk drive characteristics

Capacity of a hard disk drive is usually quoted in gigabytes. Older HDDs quoted their smaller capacities in megabytes.

The data transfer rate at the inner zone ranges from 44.2 MB/s to 74.5 MB/s, while the transfer rate at the outer zone ranges from 74.0 MB/s to 111.4 MB/s. An HDD's random access time ranges from 5 ms to 15 ms.

The physical size of a hard disk drive is quoted in inches. The majority of HDDs used in desktops today are 3.5 inches (9 cm) wide, while the majority of those used in laptops are 2.5 inches (6 cm) wide. As of early 2007, manufacturers have started selling SATA and SAS 2.5 inch drives for use in servers and desktops.

An increasingly common form factor is the 1.8 inches (5 cm) ATA-7 LIF form factor used inside digital audio players and subnotebooks, which provide up to 160GB storage capacity at low power consumption and are highly shock-resistant. A previous 1.8 inches (5 cm) HDD standard exists, for 2–5 GB sized disks that fit directly into a PC card expansion slot. From these, the smaller 1 inch (3 cm) form factor was evolved, which is designed to fit the dimensions of CF Type II, which is also usually used as storage for portable devices including digital cameras. 1 inch was a de facto form factor led by IBM's Microdrive, but is now generically called 1 inch due to other manufacturers producing similar products. There is also a 0.85 inch form factor produced by Toshiba for use in mobile phones and similar applications, including SD/MMC slot compatible HDDs optimized for video storage on 4G handsets.

The size designations are more nomenclature than descriptive. The names refer to the width of the disk inserted into the drive rather than the actual width of the entire drive. A 5.25 inches (13 cm) drive has an actual width of 5.75 inches (15 cm), a 3.5 inches (9 cm) drive 4 inches (10 cm), a 2.5 inches (6 cm) drive 2.75 inches (7 cm). A 1.8 inches (5 cm) drive can have different widths, depending on its form factor. A PCMCIA drive has a width of 54 mm, while an ATA-7 LIF form factor drive has a width of 53.85 mm.

A hard disk is defined to be at "full height" if its height is 3.25 inches (8 cm). It is "half height" at a height of 1.625 inches (4 cm). A "slim height" or "low profile" HDD has a height of 1 inch (3 cm). "Ultra low profile" drives can have heights of 0.75 inches (19 mm), 0.67 inches (17 mm), 0.49 inches (12 mm) or 0.37 inches (9 mm).

2 comments:

Anonymous said...

Hi Niki. I am impressed with your blog on HDDs. More than just reading the content, I was also interested in the layout of your site. What I particularly like about the template you have chosen is that the width of your text is not fixed - ie, the text re-formats when you change the size of the browser window. I will now look for something like that myself.

Thanks, Henrik

bcstractor said...

Hi Where did you get the picture of the 62PC? I worked on the early designs of the rotary actuator for it in Hursley UK.