Both. Double precision numbers have more bits for the exponent (so the range of values is increased) and more bits in the mantissa (so the precision is increased).
Floating point on MIPS was originally done in a separate chip called coprocessor 1 also called the FPA (Floating Point Accelerator). Modern MIPS chips include floating point operations on the main processor chip. But the instructions sometimes act as if there were still a separate chip.
MIPS has 32 single precision (32 bit) floating point registers.
$f0is not special (it can hold any bit pattern, not just zero).
(Memory Test: ) Why is
$f0 not hard-wired to contain a floating point zero,
$0 is hard-wired to contain an integer zero?