what is the storage capacity of a high-density 3.5' disk?

floppy or hard disk?

1.44 MB if it is a floppy disk. These have long been obsolete.

If it's a hard disk, as much as 1 TB (10^12 bytes) over 5 platters, or 200 GB per platter. But that number goes up constantly and may be higher than that number.

.

A bit variable, depending on who you talk to. What is on the label bears little resemblance to actual storage.

When the floppy came out, they were described as 360kb and the double sided ones were 720 kb. In due course, the High density disks appeared and were described as 1.44Mb. Shortly after they doubled the capacity to 2.88Mb. Special versions with dedicated drives also appeared with capacities as high as 240Mb (ls-240).

A problem is how the disk capacity is calculated. Unformatted, a HD disk has a capacity of 2Mb. The nominal formatted capacity printed on labels is "1.44 MB" which uses an incorrect definition of the megabyte that combines decimal (base 10) with binary (base 2) to yield 1.44×1000×1024 bytes (approximately 1.47 million bytes). This usage of the "Mega-" prefix is not compatible with the International System of Units prefixes. Using SI-compliant definitions, the capacity of a 3½-inch HD floppy is properly written as 1.47 Mb (base 10) or 1.41 Mb (base 2).

Variations in how the disk is formatted can change the capacity (formatted). The differences between formats can result in user data capacities ranging from approximately 1300 KB up to 1760 KB (1.80 MB) on a "standard" 3½-inch High Density floppy (and even up to near 2 MB with utilities like 2MGUI).

1.44MB

3.5 Inch Floppy Disk Capacity

The formated capacity of a 3.5" high density floppy diskette is 1.44MB or 720KB.