A realistic model of computation called the block-move (BM) model is d
eveloped. The BM regards computation as a sequence of finite transduct
ions in memory, and operations are timed according to a memory cost pa
rameter mu. Unlike previous memory-cost models, the BM provides a rich
theory of linear time, and in contrast to what is known for Turing ma
chines (TMs), the BM is proved to be highly robust for linear time. Un
der a wide range of mu parameters, many forms of the BM model, ranging
from a fixed-wordsize random-access machine (RAM) down to a single fi
nite automaton iterating itself on a single tape, are shown to simulat
e each other up to constant factors in running time. The BM is proved
to enjoy efficient universal simulation, and to have a tight determini
stic time hierarchy. Relationships among BM and TM time complexity cla
sses are studied.