His Master's thesis was titled A Performance Study of the Acorn RISC Machine, in which he exposed shortcomings of the early ARM designs.
[2] Jaggar joined Cambridge-based ARM in June 1991, as a programmer and initially developed the ARMulator instruction set simulator.
Secondly it suffered from poor code density, typical of a RISC instruction set, and therefore to reach its maximum performance required an expensive memory system, in terms of both cost and power consumption.
[9] The Thumb compressed instruction set was first implemented in the ubiquitous ARM7TDMI which underpinned the successful ARM licensing business model for many years.
[13] Jaggar received the 2019 James Clerk Maxwell Medal from the IEEE and RSE with fellow ARM engineer David Flynn for "contributions to the development of novel Reduced Instruction Set Computer (RISC) architectures adopted in 100 billion+ microprocessor cores worldwide".