and galactocentric positions. This is usually compared to the integrated $V$-band luminosity of the parent galaxy’s halo (as a measure of its unclustered field star population) through the so-called specific frequency (Harris & van den Bergh 1981): $$S_N\equiv {\cal N}_{\rm tot}\times10^{0.4(M_V^T+15)} \propto
{\cal N}_{\rm tot}/L_{V,{\rm gal}}\ .
\label{eq:21}$$ Even though any observational derivation of $S_N$ necessarily involves (possibly large) extrapolations of data that directly count only the brightest clusters in some spatially limited subset of a GCS, these estimates tend usually to be surprisingly robust. To date, specific frequencies have been obtained for of order 100 galaxies, some 80% of which are early-type systems (see the compilations of Harris 1991; Durrell et al. 1996; Kissler-Patig 1997; Blakeslee 1997; Blakeslee, Tonry, & Metzger 1997; Harris et al. 1998). Given this bias in the observational database, some of what follows will make use of results that are really specific to elliptical galaxies; spirals are brought more explicitly into the discussion in §4 below.

Specific frequency is easily related to the total masses of a galaxy’s GCS and of its unclustered halo stars, if both the mean mass of the individual globulars in the system and the mass-to-light ratio of the overall [*stellar*]{} 