By Kasper Jade

Published: 09:35 AM EST

Apple this week began informing its direct sales channels that several of its desktop-based Mac offerings have entered a period of constraint, further hinting that Mac hardware updates are on the horizon. [Updated with additional info on Mac mini.]

For example, Apple Retail on Monday issued an advisory to its stateside brick-and-mortar shops in which it noted that further orders for many of its existing desktop SKUs would go unhonored and that stores should not expect those models to be restocked.

More specifically, the Mac maker made the remarks in respect to all four retail configurations of its all-in-one aluminum iMac line and the low-end $599 Mac mini, which sports half the memory and roughly one-third the storage capacity of its pricier cousin.

Word of the restrictions arrive on the heels of several reports from AppleInsider's indicating that the Cupertino-based company is preparing to unveil the first makeover to its iMac (1, 2) and MacBook (1, 2) product families since the 2007 and 2006 calendar years, respectively.

Given Apple's penchant for favoring its direct channels with product inventory over those of its partners, the move implies that production of the aforementioned iMac and Mac mini models has ceased completely. Up until this week, Apple retail stores have continued to facilitate sales of those models while many resellers could not.

For instance, Amazon.com, one of the company's largest authorized Mac dealers, ran out of all four iMac configurations and both Mac mini configurations earlier this month and has shown no signs that a restocking is in order.

Although the reseller continues to list availability of the four current iMac models and two Mac mini models, its website indicates that orders for those systems won't be filled from its own inventory, but from those of partners like J&R Music and Computer Word, DataVision, Techno Intelligence, and PowerMax.

While AppleInsider has been fairly vocal over the past few months regarding Apple's plans to refresh its iMac and plastic MacBook offerings, little attention has been given to the diminutive Mac mini line. That said, it has received a handful of reports to suggest those updates may be quietly accompanied by more modest refreshes to the Mac mini line consisting primarily of component and CPU upgrades.

Update: We've received some additional confirmation that the low-end Mac mini SKU has indeed been discontinued. Volume partners wishing to place orders are being told that availability should improve in the next few weeks.

For more on Apple's upcoming Mac hardware announcements see:

Apple ready and waiting with redesigned iMac line

Apple close to unveiling all-new MacBook line

Apple to retain, redesign plastic MacBook family

Apple's next iMacs rumored with compelling new features

Apple may extend antiglare display option to more Macs

Briefly: more affordable iMacs from Apple expected by fall

Apple to introduce more affordable Macs, sources say