(projectively extended real number system) was dropped from the later formal issue of IEEE 754-1985. The 80287 retained projective closure as an option, but the 80387 and subsequent floating-point processors (including the 80187) only supported affine closure. Coprocessor interface The 8087 differed from subsequent Intel coprocessors in that it was directly connected to the address and data buses. The 8087 looked for instructions that commenced with the "11011" sequence and acted on them, immediately requesting DMA from the main CPU as necessary to access memory operands longer than one word (16 bits), then immediately releasing bus control back to the main CPU. The coprocessor did not hold up execution of the program until the coprocessor instruction was complete, and the program had to explicitly synchronize the two processors, as explained above (in the "Design and development" section). There was a potential crash problem if the coprocessor instruction failed to decode to one that the coprocessor understood. Intel's later coprocessors did not connect to the buses in the same way, but received instructions through the main processor I/O ports. This yielded an execution time penalty, but the potential crash problem was avoided because the main processor would ignore the instruction if the coprocessor refused to accept it. The 8087 was able to detect whether it was connected to an 8088 or an 8086 by monitoring the data bus during the reset cycle. The 8087 was, in theory, capable of working concurrently while the 8086/8 processes additional instructions. In practice, there was the potential for program failure if the coprocessor issued a new instruction before the last one had completed. The assembler would automatically insert an FWAIT instruction after every coprocessor opcode, forcing the 8086/8 to halt execution until the 8087 signalled that it had finished. This limitation was removed from later designs. Models and second sources Intel 8087 coprocessors were fabricated in two variants: one with ceramic side-brazed DIP (CerDIP) and one in hermetic DIP (PDIP), and were designed to operate in the following temperature ranges: C, D, QC and QD prefixes: 0 °C to +70 °C (commercial use). LC, LD, TC and TD prefixes: −40 °C to +85 °C (industrial use). MC and MD prefixes: −55 °C to +125 °C (military use). All models of the 8087 had a 40-pin DIP package and operated on 5 volts, consuming around 2.4 watts. Unlike later Intel coprocessors, the 8087 had to run