From: Chris Muller,
In the 17 months since Squeak 4.5 was released, a huge development effort took place to create the next generation virtual-machine for the Squeak / Pharo / Newspeak family of programming systems. Squeak is the modern incarnation of the Smalltalk-80 programming environment originally developed at the Xerox PARC.
“Squeak 5” introduces this new VM and associated new memory model, collectively referred to as “Spur”. Presented  by Eliot Miranda and Clément Béra at the 2015 International Symposium on Memory Management, this new VM affords Squeak applications a significant boost in performance and memory management. Among other optimizations, the #become operation no longer requires a memory scan.
Object pinning and ephemerons are also now supported. The release notes  provide more details.
The new memory model requires a new image file format. Although this new format results in about a 15% increased memory requirement for the same number…