The first surface-mount package to replace small pin count (i.e.
8-16) DIP packages. They are also called "Gull Wing" packages,
referring to the shape of their pins. Lately, they are very popular
for higher pin count (up to 64 pins), mostly memory types of ICs.
At first packages with a 50mil (1.27mm) lead pitch dominated, but
over the last few years various higher density versions became popular.
These have acronyms such as SSOP, TSOP, TSSOP and so on, indicating
features such as smaller (shrunk)pitch or thin package height.
SOP Pitch: 1.27mm
SSOP Pitch: 0.4, 0.5 or 0.65mm
TSOPs: (See Link)