Conversion from 4 Teraoctets to Megabits

Information about the Teraoctet (To)

The teraoctet is a unit of digital information equal to one million million octets, or a thousand gigaoctets. Its symbol is To. It is the unit of the modern hard drive, and the point at which personal storage stopped being something anyone needed to manage carefully.

A teraoctet holds roughly two hundred and fifty thousand photographs from a phone, or two hundred hours of high-definition video, or a quarter of a million songs. For a person who is not a professional photographer or video editor, a single teraoctet is more storage than a lifetime of ordinary files will fill.

Consumer hard drives crossed one teraoctet in 2007 and now reach twenty or more. Solid-state drives arrived at the same capacities more slowly and at higher cost, but with far greater speed, and the two technologies now divide the market between capacity and performance rather than competing directly.

The teraoctet is where the decimal-binary discrepancy becomes visible enough to annoy. A drive sold as one teraoctet holds a million million octets exactly; the operating system divides by 1,024 four times and reports 0.909 tebioctets, which it usually labels as 931 gigaoctets. The shortfall appears to be 7 per cent, though nothing has actually been lost. At the petaoctet the same arithmetic produces a 12 per cent gap.

Backup and archiving live at this scale. A household's complete collection of photographs, documents and video typically fits in a few teraoctets, which is why external drives are sold in exactly that range. Cloud storage services price in teraoctets too, and the economics of keeping a second copy of everything only work because the unit price of storage has fallen faster than the quantity has grown.

In professional work the teraoctet is a daily quantity rather than a milestone. A day of filming in high resolution produces several teraoctets of raw footage. A genome sequencing run produces a few hundred gigaoctets, so a modest laboratory generates teraoctets a week. Both fields have had to build workflows around moving data that will not fit on any network in reasonable time.

One teraoctet equals 1,000,000,000,000 octets, 1,000 gigaoctets, 8 terabits, or about 0.9095 tebioctets.

Information about the Megabit (Mbit)

The megabit is a unit of digital information equal to one million bits. Its symbol is Mbit. It is the unit in which the speed of an internet connection is almost always advertised, which makes it one of the few data units that ordinary consumers encounter by name every time they choose a service.

A megabit is one million bits exactly, not 1,048,576. That distinction has practical consequences. A megabit holds 125,000 octets, which is 125 kilooctets, so a connection running at 100 megabits per second transfers about 12.5 megaoctets per second at best. A file listed as 500 megaoctets therefore takes a minimum of forty seconds, not the four the advertised number seems to promise.

That factor of eight is the reason so many people believe their connection is slower than they were sold. Nothing dishonest is happening: the industry quotes throughput in bits per second because that is what the physical layer actually carries, while file managers quote size in octets because that is how storage is organised. Both conventions are correct in their own domain, and the arithmetic between them is a division by eight.

Real throughput is lower still. Protocol headers, error correction and retransmission all consume capacity, and the usable share of a link is typically 90 to 95 per cent of its nominal rate. Wireless links lose more, because the medium is shared and interference forces retries. A connection advertised at 100 megabits per second commonly delivers 90 or so in practice, and less over a busy wireless network.

The numbers that define the eras are worth remembering. Early broadband offered 1 to 8 megabits per second, cable and fibre pushed that to 50 and 100, and gigabit services are now common in cities. High-definition video streaming needs roughly 5 megabits per second, ultra-high-definition roughly 25, and a video call between two 8, so a household's real requirement is usually far below what it buys.

In memory the megabit describes chip capacity. A 512-megabit memory chip holds 64 megaoctets, and several such chips make a module. Manufacturers count in bits because that is what the silicon holds; buyers count in octets because that is what the operating system reports.

One megabit equals 1,000,000 bits, 1,000 kilobits, 125 kilooctets, or about 0.9537 mebibits.