Register windows is an architectural technique that re- duces memory operations required to save and restore reg- isters across procedure calls. Its effectiveness depends on the size of the register file. Such register requirements are normally increased for out-of-order execution because it re- quires registers for the in-flight instructions, in addition to the architectural ones. However, a large register file has an important cost in terms of area and power and may even affect the cycle time. In this paper we propose two early register release techniques that leverages register windows to drastically reduce the register requirements, and hence reduce the register file cost. Contrary to the common belief that out-of-order processors with register windows would need a large physical register file, this paper shows that the physical register file size may be reduced to the bare mini- mum by using this novel microarchitecture. Moreover, our proposal has much lower hardware complexity than previ- ous approaches, and requires minimal changes to a conven- tional register window scheme. Performance studies show that the proposed technique can reduce the number of phys- ical registers to the same number as logical registers plus one (minimum number to guarantee forward progress) and still achieve almost the same performance as un unbounded register file.