Why was it hard to program Cray machines ?
There has always been lots of Unix src code sloshing round on the net since well before Linux and the admirable open src code movement was invented. However there were a couple of things about Cray machines that made porting codes to Cray machines tricky. We won’t get into what you had to do to your algorithm to get the best out of a Cray machine but just examine a few things that made the conversion of codes to Cray machines interesting. Firstly there was the word size, one rather large size fitted all, integers and floats were represented in 64 bits, whereas most other machines used 16 or 32 bit for ints and floats. This would not cause a problem in well written codes unless assumption were made about the range of an integer or the relative sizes of integers to character data types. Cray PVP machines are word addressable, the T3D and T3E are byte addressable machines. Although the compilers used transparent word division to mimic byte addressable constructs on PVP machines, advanced
