Yes, prior to 4.x processes were strictly limited to 64kb code and 64kb data - essentially the equivalent to what MS-DOS programmers would call the small memory model only. There are a bunch of reasons for this, all of which stem from the fact every part of Mark Williams C and the assembler/linker toolchain hewed so closely to the exact model set by V6 UNIX - including the same .o and .a formats, hence the same limitations all down the line.

Since so much my previous work before joining work on Coherent was on embedded toolchains and DOS development, the fact that so little use anywhere was made of x86 segmentation was surprising to me, but I knew all the V6 internals well enough to adapt back.

Even in 4.0 where the COFF and the iBCS2 syscalls all worked, actually most of the userland still stayed as 16-bit small model since the aim was to keep most of the installation process the same, which was that essentially the first install floppy was a reasonably full live system. Obviously things grew a ton and during the evolution of 4.0 we slowly had to move the bulk of the 32-bit userland components off to packages in later floppies.