Around the AM4 socket, we see that the TOMAHAWK B350 features a 4+2 power phase design. To the right there is a 4pin CPU fan header, with an additional 4pin system fan header on the left. Note, there is no dedicated RGB LED header for the Ryzen 7 coolers.
MSI have implemented DDR4 BOOST technology, allowing a memory frequency of up to 3200MHz OC. The PCB has clearly marked which DIMM lanes to prioritise, though this is likely done as there is no colour coding as they are all black. Along the edge there are two more 4pin fan headers, one of which can output 2a for waterpumps. Just to the right of the 24pin ATX power socket there is a row of 4 LEDs for the EZ Debug feature.
The TOMAHAWK features a right angle USB 3.1 Gen1 connector, allowing for more convenient cable routing of the front panel connectors. Of the 4x SATA 6Gb/s ports, only two are right angle, which seems to be a little counter intuitive. To the left of the SATA ports, there is another 4pin fan header.
To the left there is a PCIe to PCI lane converter as MSI have intentionally added 2x legacy PCI slots for compatibility with older devices, this will be a positive for some, a negative for others. Additional internal headers include: Front panel audio, RGB LED header, 1x 4pin fan header, serial port, parallel port, TPM module connector, 2x USB 2.0 headers, a second USB 3.1 Gen1 header, and the front panel headers.
The audio solution is based around audio-grade capacitors, the Realtek ALC892 and some dedicated circuitry.
There is a single dedicated M.2 port that is seated underneath the primary 16x PCIe slot.
The rear IO consists of a single universal PS/2 port, 2x Gaming Device USB 2.0 ports, VGA, DVI-D, HDMI 1.4, 3x USB 3.1 Gen 1 (type A). 1x USB 3.1 Gen1 (Type C), LAN port, and 6x Gold plated OFC audio jacks.