Atmospheric pressure. 1 atm = 101.3 kPa (that's kilo-pascals for the uninitiated).

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This write-up is dedicated to czeano

ATM is a packet-switching technology that uses 53-byte cells to support voice, video, data, and images. These cells, of which 48 bytes are data, allow for reduced delay and variance of jitter. It is broken up into four layers: Physical layer, Transmission Convergence layer, ATM layer, and ATM Adaption layer (AAL). The details of these layers and their sub-layers would require a much longer write-up, and I'm simply too busy playing Grim Fandango right now.

ATM can be used as a high-speed underlying technology for Frame Relay on campus networks, for example, or to interconnect high-speed LANs. ATM switches offer connection speeds up to OC-12 (622 Mbps) and desktop connections up to OC-3 (155 Mbps).

The ATM Forum was established in 1991, and you can find all kinds of ATM information at As a side note, whenever an ATM problem came up at work in the year 2000, even the best of us freaked out, because only a few clients recently had it implemented: "Do you know anything about ATM?" "No." "Do you know anything about ATM?" "No." And so on. Good times...

ATM is also an acronym for "At the Moment"; for example, "I haven't got any new books ATM."

Used almost exclusively on the Internet, due to its relative unpronounceableness.

It should be noted that the 53-byte size of an ATM-cell is due to the dumbest compromise in the history of telecommunication.

53 bytes is the sum of 48 bytes payload and 5 bytes overhead.

The telephony people involved with the ATM negociations wanted a 32 byte payload, because low payload means low transmission delay (You don't have to wait for a zillion bytes prior to send, you don't have to wait for a zillion bytes prior to send to the DAC).

The data people trusted the technology, and didn't want to waste 5 bytes every 32 payload bytes. So they wanted twice as much payload per cell.

The fighting was ended when they decided to make everybody happy : they took the mean between 32 bytes and 64 bytes and chose to use 48 bytes, which is a pleasure to implement, especially in hardware.

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