We Need 25 More

The joke hinges on a classic data storage pun. 999 megabytes is just shy of 1 gigabyte (1000 MB), so the band hasn't "gotten a gig" yet. It's like watching a storage progress bar stuck at 99.9% - technically running, but not quite there. Storage engineers probably tell this joke at data center happy hours right before everyone silently finishes their drinks.