Ram is not thread safe
Ram is a singleton, if it's being used from two threads, CME will happen.
https://github.com/objectionary/eo/blob/master/eo-runtime/src/main/java/EOorg/EOeolang/Ram.java
https://github.com/objectionary/eo/blob/master/eo-runtime/src/main/eo/org/eolang/ram.eo
diff --git a/eo-runtime/src/main/java/EOorg/EOeolang/Ram.java b/eo-runtime/src/main/java/EOorg/EOeolang/Ram.java
index c0520bfd7..a22e10ec2 100644
--- a/eo-runtime/src/main/java/EOorg/EOeolang/Ram.java
+++ b/eo-runtime/src/main/java/EOorg/EOeolang/Ram.java
@@ -32,8 +32,8 @@ import java.io.RandomAccessFile;
 import java.io.UncheckedIOException;
 import java.lang.management.ManagementFactory;
 import java.nio.file.Files;
-import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 import org.eolang.Dataized;
 import org.eolang.Phi;
 
@@ -51,7 +51,7 @@ public enum Ram {
     /**
      * Phi to File mapping.
      */
-    private final Map<Phi, RandomAccessFile> addresses = new HashMap<>();
+    private final Map<Phi, RandomAccessFile> addresses = new ConcurrentHashMap<>();
 
     /**
      * Read.
diff --git a/eo-runtime/src/test/java/EOorg/EOeolang/RamTest.java b/eo-runtime/src/test/java/EOorg/EOeolang/RamTest.java
index 6ec564bd4..5886561db 100644
--- a/eo-runtime/src/test/java/EOorg/EOeolang/RamTest.java
+++ b/eo-runtime/src/test/java/EOorg/EOeolang/RamTest.java
@@ -7,6 +7,8 @@ import org.eolang.PhWith;
 import org.eolang.Phi;
 import org.hamcrest.MatcherAssert;
 import org.hamcrest.Matchers;
+import org.junit.jupiter.api.parallel.Execution;
+import org.junit.jupiter.api.parallel.ExecutionMode;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.CsvSource;
 
@@ -14,6 +16,7 @@ import org.junit.jupiter.params.provider.CsvSource;
  * Test for {@link Ram}.
  * @since 1.0
  */
+@Execution(ExecutionMode.CONCURRENT)
 final class RamTest {
     @ParameterizedTest
     @CsvSource({
['eo-runtime/src/main/java/EOorg/EOeolang/Ram.java', 'eo-runtime/src/test/java/EOorg/EOeolang/RamTest.java']