Each of the first 6 User Thread Memory Spaces are limited to 64KBytes (65536 Bytes). Thread 7 is larger and limited to 5x64KBytes (327680Bytes).
If subsequent Threads are unused it is possible permitted to overflow into their Thread Spaces. For example, if Threads #2 and #3 are not used is permissible to load a program of size 3 x 64KBytes (196608 bytes) into Thread #1. If you later want to use Threads #2 or #3 then Thread #1 should be halted before using them.