This section explores the memory behavior of the PHP benchmarks through three characterizations—gross allocation behavior, heap composition, and object size demographics. We use this analysis to characterize the benchmarks and contrast them with the demographics of SPECjvm98 benchmarks [8, 9]. We choose SPECjvm98, as opposed to the real world more sophisticated Java DaCapo [10] benchmarks, because today’s PHP benchmarks and VM technology are at a similar, early point in their development, as were Java benchmarks and VM technology when SPECjvm98 was introduced.