Per Dornyei (2005) (55-9).
"...one of the most promising current directions in language aptitude studies", (55).
"working memory for language may be one (if not the) central component of this language aptitude". (Miyaki and Friedman, 1998 ).
Relying on Baddely and Hitch (1974 - no ref given) as reviewed in Baddely (2003), Dornyei reports a four part structure to working memory:
1 The phonological loop, the verbal component, responsible for storing verbal and acoustic information. It decays within 2 seconds, but loss is prevented by "subvocal rehearsal".
2 The visuospatial sketchpad, the visual counterpart to (1), used, eg, in everyday reading. Baddely suggests it also has a storage/processing component, which can translate verbal to visual information.
3 The central executive, "the most important and least understood aspect of working memory", it is the "supervisory attentional system". It's thought that "the executive processes are... the principal factors determining individual differences in 'working memory span'".
4 The episodic buffer, a recently added component, a storage counterpart to the central executive, combining information from various sources into "a multi-facted code or episode".
Baddely, A.D. (2003) Working memory and language: An overview. Journal of Communication Disorders, 36 189-208.
Miyake, A., & Friedman, D. (1998) Individual differences in second language proficiency: Working memory as language aptitude. In A.F Healy and L.E. Bourne (Eds.), Foreign Language Learning: Psycholinguistic studies on training and retention (pp 339 - 364) Mahwah, NJ: Lawrence Elbaum Associates.