Yes, in a shared memory system like the von Neumann architecture, instructions and data coexist in the same memory space, which means there is a theoretical risk that instructions could be misinterpreted as data or vice versa. However, modern systems implement several safeguards to prevent this. Firstly, programs are compiled with clear structure and designated memory regions for code and data. Compilers and linkers ensure that the CPU executes only memory locations intended to be instructions. Secondly, operating systems use memory protection features, such as setting permissions for each segment of memory. For example, some memory regions are marked as “read-only” or “execute-only” to stop data from being accidentally run as code. Additionally, technologies like the execute-disable (XD) bit prevent certain areas of memory from being executed even if they contain binary data. These mechanisms, combined with hardware-level features such as memory segmentation and virtual memory management, significantly reduce the risk of such misinterpretations.

In shared memory systems, memory addressing schemes are essential because the processor needs a method to distinguish and access specific memory locations where instructions and data are stored. Although instructions and data use the same address space, the processor treats them differently based on the stage of execution. During the fetch phase, the program counter holds the address of the next instruction to execute. This address is incremented sequentially, or updated by control flow instructions like jumps or branches. During the execution phase, the instruction itself might contain an operand that refers to a memory address holding data. For example, an instruction like “LOAD 0101” tells the CPU to fetch the data from address 0101. Therefore, while both use the same addressing scheme, the CPU distinguishes between them contextually: instruction addresses come from the program counter, and data addresses come from within the instruction's operands. This dual use of addresses allows flexible and powerful control of execution and memory access.

Caching plays a critical role in mitigating the performance limitations of shared memory systems, particularly addressing the von Neumann bottleneck. In these systems, the CPU must use the same bus to fetch both instructions and data, which can create a delay when both are needed at the same time. To alleviate this, modern processors use separate cache layers: an instruction cache (I-cache) and a data cache (D-cache). The instruction cache stores recently used instructions, allowing the CPU to quickly retrieve them without accessing main memory again. Similarly, the data cache holds recently accessed data values. This separation allows the CPU to fetch an instruction and access data concurrently, despite both being stored in the same RAM. Additionally, these caches are much faster than RAM, often made from static RAM (SRAM), which further enhances performance. Advanced processors may also include level 2 (L2) and level 3 (L3) caches, shared across cores, to further reduce latency and memory access time.

When a program modifies its own instructions—known as self-modifying code—it alters the contents of memory locations that hold its machine code. In early computing, this was used to optimise performance or reduce instruction count. In shared memory systems, self-modification is technically possible because both instructions and data are stored in the same memory and can be accessed and altered using the same instructions. However, in modern systems, this is heavily restricted due to security and stability concerns. Most operating systems now mark code segments as non-writable and executable, and data segments as writable but non-executable. Attempting to modify code segments typically results in a segmentation fault or access violation error. If modification is required—such as in Just-In-Time (JIT) compilers—the system will temporarily allow write access, modify the code, and then reset the memory protection. These protections are enforced through hardware and OS-level memory management units to prevent vulnerabilities like code injection or buffer overflow attacks.

Virtual memory systems manage shared memory by creating an abstraction where each program believes it has access to a continuous and isolated block of memory. This is achieved by mapping virtual addresses used by programs to physical addresses in RAM using a hardware component called the Memory Management Unit (MMU). In this model, instructions and data are still stored in the same physical memory, but virtual memory allows the operating system to assign separate logical regions for code and data, even within the same program. For example, the OS might allocate virtual addresses 0x0000–0x3FFF for executable code and 0x4000–0x8FFF for data. These mappings are recorded in page tables, and access rights can be assigned to each page—such as read, write, or execute. This allows the system to prevent a program from writing to its own code or executing data. Virtual memory also enables features like paging and swapping, where less-used memory contents are temporarily moved to disk to free up RAM, improving multitasking and memory efficiency.