Sun's Niagara line of processors had similar numbers of threads (64/128), but they often had lacklustre performance. With this amount of parallelism, it becomes

Sun's Niagara line of processors had similar numbers of threads (64/128), but they often had lacklustre performance. With this amount of parallelism, it becomes very difficult to keep all the threads busy, even for highly scalable programs. You'd get hit by all kinds of problems, like blockages due to memory throughput, or shared resources (IIRC the Niagara threads shared FPUs and other processing blocks, so to get them all running 100% of the time you'd have to manage the workload of your tasks insanely carefully) On top of that, so much stuff just doesn't scale well. On the early Niagaras, even ssh-ing into the machine was noticeably slow. Oh? your crypto doesn't use all 64 threads? Hard luck!