The term "virtual machine" initially described a 1960s operating system concept: a software abstraction with the looks of a computer system's hardware (real machine). Forty years later, the term encompasses a large range of abstractions - for example, Java virtual machines that don't match an existing real machine. Despite the variations, in all definitions the virtual machine is a target for a programmer or compilation system. In other words, software is written to run on the virtual machine.
The history of computing has been characterized by continuous transformation resulting from the dramatic increases in performance and drops in price described by Moore's law. Computing "power" has migrated from centralized mainframes/servers to distributed systems and the commodity desktop. Despite these changes, system sharing remains an important tool for computing. From the multitasking, file-sharing, and virtual machines of the desktop environment to the large-scale sharing of server-class ISP hardware in collocation centers, safely sharing hardware between mutually untrusting parties requires addressing critical concerns of accidental and malicious damage.
Simulators are a form of "virtual machine" intended to address a simple problem: the absence of real hardware. Simulators for past systems address the loss of real hardware and preserve the usability of software after real hardware has vanished. Simulators for future systems address the variability of future hardware designs and facilitate the development of software before real hardware exists.
Many developers see buffer overflows as the biggest security threat to software and believe that there is a simple two-step process to secure software: switch from C or C++ to Java, then start using SSL (Secure Sockets Layer) to protect data communications. It turns out that this naïve tactic isn't sufficient. In this article, we explore why software security is harder than people expect, focusing on the example of SSL.
In today's competitive, fast-paced computing industry, successful software must increasingly be: (1) extensible to support successions of quick updates and additions to address new requirements and take advantage of emerging markets; (2) flexible to support a growing range of multimedia data types, traffic flows, and end-to-end QoS (quality of service) requirements; (3) portable to reduce the effort required to support applications on heterogeneous operating-system platforms and compilers; (4) reliable to ensure that applications are robust and tolerant to faults; (5) scalable to enable applications to handle larger numbers of clients simultaneously; and (6) affordable to ensure that the total ownership costs of software acquisition and evolution are not prohibitively high.
As a teenager, James Gosling came up with an idea for a little interpreter to solve a problem in a data analysis project he was working on at the time. Through the years, as a grad student and at Sun as creator of Java and the Java Virtual Machine, he has used several variations on that solution. "I came up with one answer once, and I have just been repeating it over and over again for a frightening number of years," he says.
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