1U server

In computing, a pizza box is a style of case for computers or network switches. Cases of this type tend to be wide and flat, normally one or two rack units (1U or 2U, 1¾ or 3½ inch, 4.4 or 8.9 cm) in height, thus resembling pizza delivery boxes. ... The density of computing power and stackability of pizza box systems also made them attractive for use in data centers. Systems originally designed for desktop use were placed on shelves inside of 19‑inch racks, sometimes requiring that part of their cases be cut off in order for them to fit. ... Servers in this form factor, as well as higher-end Ethernet switches, are now designed for rack mounting. Rack mount 1U computers come in all types of configurations and depths. [Pizza box form factor. Wikipedia]