Sun on Monday is set to light up its long-delayed public computing grid allowing users to book central processing unit hours with a credit card through a Web-based portal, company officials said.The company first promised to turn on the public grid last year, but has delayed the roll out. Reasons for the delay depend on whom you ask at Sun, but have included security issues, development hurdles and a redirected focus on Sun's enterprise grid computing efforts.In the past year, Sun has referred to the public grid both as the "retail grid" and the "SMB (small to midsize business) grid." While the target market is not yet clear, the gist of it is that users can visit a Web site, sign up for grid services via PayPal and load their programs to be processed on Sun's infrastructure."Sun has been promising a publicly accessible grid for a long time now, but I've seen the interface for the public grid and it appears they're about ready to turn the public side on" said analyst Jonathan Eunice, of Illuminata. "But the real trick for Sun is getting it up and available as opposed to having a glorious interface. Where is it? That's the issue."However, Eunice noted one advantage of the delayed launch is that Sun has "now done a fair amount of work on the enterprise side, and they've gained a bit of experience in how to scale it up and build it up as stresses occur and resource needs grow."Sun says for the past eight months it has been offering grid services for enterprise customers that want to outsource large computational workloads. But unlike the public grid, these enterprise-geared services are purchased through Sun sales channels and involve typical corporate contractual agreements. HP and IBM also offer similar computing services.The infrastructure is mostly the same behind Sun's enterprise and public grid offerings, except that enterprise grid users have the option to use Linux while public grid users will exclusively run on Sun's Solaris 10 operating system, said Aisling MacRunnels, senior director of utility computing for Sun.Enterprise users also have the option to block out a specific amount of grid resources for a specific period of time in advance and have a dedicated machine they can use to access the grid with a VPN-type connection, as opposed to going through the Internet for the public grid.So, who will use the public grid?"There are a couple of models that are easy to imagine," Eunice said. For example, architects could use the grid services to quickly generate rendered models to show walkthroughs to clients, he said.Sun has about a dozen beta customers willing to speak as references for the public grid after the launch next week, but officials wouldn't say if that's the total number of beta users. The company did say that during beta testing it demonstrated that it could support 2,000 concurrent users.Sun will charge public grid users $1-per CPU-per hour. Sun had previously said there would be a 4-hour minimum required, but now the company says "a buck will do" as a minimum.New accounts could take up to 24 hours to process, as it has to check names against a U.S. federal list of prohibited users, Sun said. This isn't the first time Sun has indicated that the federal government has some oversight into its grid efforts -- it recently said that federal restrictions prohibit it from offering grid resources globally."This type of use case is new and we do expect regulations will evolve with utility computing and we will continue to support those standards as they evolve," MacRunnels said. "We will be rolling out to the U.S. first, with other countries to follow. The plan is to roll out to the U.K. in about six months and we're in discussions with partners in other countries in Europe and Asia."