Sign In

Communications of the ACM

Research highlights

Technical Perspective: Unexpected Connections

Scalability is the capability of a parallel program to speed up its execution as we provide it with more CPUs. Back in 1967, Gene Amdahl noticed the sequential part of a parallel program had a disproportionate influence on scalability.1 Suppose that some program takes 100 s to run on a sequential processor. Now, let's run it on a parallel computer. If we are able to parallelize, say, 80% of the code, then with enough CPUs that 80% would take essentially zero time. However, the remaining sequential portion will not run any faster; this means the parallel program will always take at least 20 s to run, a maximum speed-up of only 5X. If we are able to parallelize 95% of the code, speedup is still limited to 20X, even with an infinite number of CPUs! This back-of-the-envelope calculation, known as Amdahl's Law, does not take into account other factors, such as increased memory size, but remains an important guideline.

In 1967, parallelism was a niche topic, but not any more. Improving program performance on today's clusters, clouds, and multicore computers requires the developer to pay serious attention to scalability. The inherent scalability of an interface is the focus of the following paper.


No entries found

Log in to Read the Full Article

Sign In

Sign in using your ACM Web Account username and password to access premium content if you are an ACM member, Communications subscriber or Digital Library subscriber.

Need Access?

Please select one of the options below for access to premium content and features.

Create a Web Account

If you are already an ACM member, Communications subscriber, or Digital Library subscriber, please set up a web account to access premium content on this site.

Join the ACM

Become a member to take full advantage of ACM's outstanding computing information resources, networking opportunities, and other benefits.

Subscribe to Communications of the ACM Magazine

Get full access to 50+ years of CACM content and receive the print version of the magazine monthly.

Purchase the Article

Non-members can purchase this article or a copy of the magazine in which it appears.
Sign In for Full Access
» Forgot Password? » Create an ACM Web Account