Looking at the Russian Wikipedia for the EVM S5-21, the specs are quite good:
Microcomputer based on a single-chip 16-bit N-MOP microprocessor K586VM1 (old name K586IK1). The developer of the microprocessor is A. V. Palagin.
- Processor "Electronics MS2716". Processor K586VM1.
- Bit depth - 16 bits
- The number of basic commands is 31, the command system is the same for the Electronics S5 family
- Clock frequency - 2 MHz
- Speed - approximately 200 thousand register-register commands per second
- 16 general purpose registers for each of 16 tasks
- Addressable memory - 32K 16-bit words (64 KB)
- Built-in RAM - 512 bytes (four K586RU1 chips with a capacity of 256 4-bit words each)
- Built-in ROM - 4096 bytes (two K586RE1 chips with a capacity of 1024 16-bit words, 350 ns access time)
- 64 parallel channels, four K586BB1 chips, each with a tunable 8-bit structure and two 8-bit I/O channels
- Eight K155IE7 chips forming a frequency grid
- Power consumption - no more than 20 W
The processor can execute the “core” of 16 instructions in hardware, the remaining 15 instructions are executed in firmware. Total number of teams with modifications - 256
The processor module "Electronics S5-21" contains two MPI channels , the first channel is used for communication with local input-output devices, and the second one is used for machine-to-machine communication in multiprocessor complexes and for communication with shared devices.
Also looking at the photo of board, this is several generations ahead of the two boards in your question.
So definitely not a peripheral, and I'd assume they come from a much earlier, totally unrelated system, if they are cards from a computer at all.
From the integration density, the first one looks similar to the Flip Chip modules that made up the earlier PDP minicomputers.
Since you wrote in the comments "only going for the S5 21 board": The Russian Wikipedia also mentions the main parallel interface (MPI), and on the page for that states:
The main parallel interface ( MPI ) is a standard that defines a set of lines and procedures for exchanging a processor and peripheral modules inside a computer using a combined (multiplex) address and data bus. The standard provides for an exchange rate of up to 5.6 MB / s with a transmitted data width of 8 or 16 bits and an address width of 16 to 24 bits and was focused on use in systems of low and medium performance. The requirements of the standard are set out in OST 11.305.903-80 and GOST 26765.51-86.
Electronics S5 computers , starting with Electronics S5-21, use the MPI as a bus for communicating with external devices. The Elektronika S5-21 model has two separate MPI channels: one for communication with local devices, the second for organizing machine-to-machine communication and connecting shared external devices when organizing multi-machine complexes. Connector - GRPMSh-1-61.
It also lists the signals. If these are the external connectors of your board, you'll probably need a digital signal analyzer to make sense of the signals (in particular if they are trying to read from external ROM during boot), and then you'll need something to simulate the missing cards. Quite a project.