PiTray mini is a Model B liked carrier board for building cluster with Raspberry Pi Computed Module 4 (CM4). PiTray mini focuses on providing a neat and budget solution for CM4 applications. With the same outline and mounting holes with Raspberry Pi Model B, it can be stacked upon the existed cluster. CM4 got some advantages over Raspberry Pi 4B in industrial applications. With the variants that embed eMMC storage, no matter solo setup or cluster application would be much more reliable and fast on disk I/O. At the same time, since CM4 provides models without wifi and Bluetooth chip, the new cluster would be more efficient in energy consumption, the O/S could disable these modules to save its computing resource. What cluster builders look for is a minimal layout with solid module mounting with powering and Gigabit Ethernet. PiTray mini got all of that.
Moreover, PiTray mini acts as a good starter kit for CM4. For CM4 variants with eMMC, there is an eMMC boot switch on board that just makes it a lot easier to flash Operation System image to eMMC, no need to spend time to figure out which pins should be connected to make the job done. It also includes a micro SD card socket to support CM4 Lite (without eMMC and requires a micro SD card).
To fit Compute Module 4 on a business card size carrier, PiTray mini does not include DSI, CSI sockets, audio jack, dual micro HDMI or USB3.0 hub because they are seldom applied in cluster building. Instead, it provides only one USB2.0, full-size HDMI, and HAT connectors that come natively from the chip. So it would still work sufficiently and economically for HTPC maker, RetroPie fans, and the majority of regular Raspberry Pi users, offering a similar experience to Raspberry Pi Model B.