Each atom record has ~60 bytes (x, y, z, occupancy, bond list, resid, segid, atom name, plus higher-level structure information about secondary structure, connected fragments, etc.) We had our own display list, so another (x, y, z, r, color-index) per atom, giving 20 more bytes. We probably used a GL/OpenGL display list for the sphere, and immediate mode to render that display list for each point, so all-in-all about 100 bytes per atom, which just barely fits in 128 MB.
That was also all single-threaded, with a ~0.1 Hz frame rate. Again, in the 1990s.
I wanted to see what more recent projects have done. Google Scholar found "cellVIEW: a Tool for Illustrative and Multi-Scale Rendering of Large Biomolecular Datasets" (2017) at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5747374/ which says
> The most widely known visualization softwares are: VMD [HDS96], Chimera [PGH04], Pymol [DeL02], PMV [S99], ePMV [JAG11]. These tools, however, are not designed to render a large number of atoms at interactive frame-rates and with full-atomic details (Van der Walls or CPK spherical representation). Megamol [GKM15] is a state-of-the-art prototyping and visualization framework designed for particle-based data and which currently outperforms any other molecular visualisation software or generic visualization frameworks such VTK/Paraview [SLM04]. The system is able to render up to 100 million atoms at 10 fps on commodity hardware, which represents, in terms of size, a large virus or a small bacterium.
Following that is a section on Related Work:
> With their new improvement they managed to obtain 3.6 fps in full HD resolution for 25 billion atoms on a NVidia GTX 580, while Lindow et al. managed to get around 3 fps for 10 billions atoms in HD resolution on a NVIDIA GTX 285. Le Muzic et al. [LMPSV14], introduced another technique for fast rendering of large particle-based datasets using the GPU rasterization pipeline instead. They were able to render up to 30 billions of atoms at 10 fps in full HD resolution on a NVidia GTX Titan
Checking up on VMD, in "Atomic detail visualization of photosynthetic membranes with GPU-accelerated ray tracing" from 2016:
> VMD has achieved direct-to-HMD rendering rates limited by the HMD display hardware (75 frames per second on Oculus Rift DK2) for moderate complexity scenes containing on the order of one million atoms, with direct lighting and a small number of ambient occlusion lighting samples.
Those citations are 6-7 years ago, which make me scratch my head wondering why ChimeraX can't handle a picornavirus.