Capacity and access speed:
PC hard disk drive capacity (measured in GB). The vertical axis is logarithmic, so the accurate line corresponds to exponential growth.
By using rigid disks and sealing the unit permit much tighter tolerances than in a floppy disk drive. As a result, hard disk drives can store more data than floppy disk drives and may access and transmit it quicker.
The exponential increases in data access speeds of HDDs and disk space and have enabled the commercial viability of consumer products that need large storage capacities, such as digital audio players and digital video recorders and.
The major way to decrease access time is to amplify rotational speed, so reducing rotational delay, though the major way to increase and storage capacity and throughput is to increase areal density. Based on historic trends, analysts guess a future growth in HDD bit compactness (and therefore capacity) of about 40% per year. Access times have not kept up having throughput increases, which themselves have not kept up with increase in storage capacity.
First 3.5″ HDD marketed as capable to store 1 TB was the Hitachi Desk star 7K1000. It have 5 platters at about 200 GB each, providing 1 TB (935.5 GiB) of usable space; note the dissimilarity among its capacity in decimal units (1 TB = 1012 bytes) and binary units (1 TiB = 1024 GiB = 240 bytes).