diff --git a/Q6-cache/Makefile b/Q6-cache/Makefile
new file mode 100644
index 0000000..54d8fc1
--- /dev/null
+++ b/Q6-cache/Makefile
@@ -0,0 +1,32 @@
+SHELL := /bin/bash
+
+######################################################################
+### EXECUTABLES
+
+CC    = gcc
+FLAGS = -O3 -Wall -std=gnu99
+RM    = rm -rf
+LINK  = -lm
+
+######################################################################
+### TARGET FILES
+
+MAIN = matmul
+
+######################################################################
+### CLEAN-UP FILES
+
+FILES_CLEAN = $(MAIN) *~
+
+######################################################################
+### COMMANDS -- ! DO NOT CHANGE BELOW !
+
+all: $(MAIN)
+
+$(MAIN): $(MAIN).c
+	$(CC) $(FLAGS) $(DEFS) $^ -o $@ $(LINK)
+
+clean:
+	$(RM) $(FILES_CLEAN) *.o *~
+
+.PHONY: $(MAIN)
diff --git a/Q6-cache/matmul.c b/Q6-cache/matmul.c
new file mode 100644
index 0000000..38685cd
--- /dev/null
+++ b/Q6-cache/matmul.c
@@ -0,0 +1,110 @@
+/*!
+  \file   matmul.c
+  \brief  Matrix multiplication implementation.
+
+  \author Nikos Pitsianis
+  \author Dimitris Floros
+  \date   2020-05-05
+*/
+
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+#include <sys/time.h>
+#include <assert.h>
+
+#define MAX_ITER 10
+#define sub2ind(i,j,n) (j) + (i)*(n)
+
+/*
+ * matrixMult - Matrix multiplication
+ */
+void matrixMult(float * const C,            /* output matrix */
+                float const * const A,      /* first matrix */
+                float const * const B,      /* second matrix */
+                int const n) {              /* number of rows/cols */
+
+  for (int i = 0; i < n; i++) {             /* rows */
+    for (int j = 0; j < n; j++) {           /* cols */
+
+      /* initialize output value */
+      C[ sub2ind(i,j,n) ] = 0;
+
+      for (int k = 0; k < n; k++) {         /* accumulate products */
+        C[ sub2ind(i,j,n) ] +=
+          A[ sub2ind(i,k,n) ] * B[ sub2ind(k,j,n) ];
+      }
+      
+    }
+  }
+      
+} // end function 'matrixMult'
+
+/*
+ * matrixInitAdd:
+ *  Initialize matrix with random indices and return the matrix
+ *  pointer.
+ *                 
+ */
+float * matrixInit(int const n) {
+
+  float *M = (float *) malloc( n*n*sizeof(float) );
+  
+  for (int i = 0; i < n; i++)              /* rows */
+    for (int j = 0; j < n; j++)            /* cols */
+      M[ sub2ind(i,j,n) ] = (float)rand()/(float)(RAND_MAX);
+
+  return M;
+  
+} // end function 'matrixInitAdd'
+
+int main(int argc, char **argv)
+{
+
+  struct timeval start, end;    /* time structs */
+  double time = 0.0;            /* execution time in ms */
+  float *A, *B, *C;             /* matrix declarations */
+  int n;                        /* matrix size */
+
+  /* read matrix size (or use default) */
+  if (argc != 2){
+    fprintf( stderr, "Uasge:\n %s n\n   where n is the matrix size.\n",
+             argv[0]);
+    exit(1);
+  }
+  n = atoi( argv[1] );
+  
+  /* initialize matrices */
+  A = matrixInit( n );
+  B = matrixInit( n );
+  C = (float *) malloc( n*n*sizeof(float) );
+  
+  /* compute matrix multiplication */
+  for (int it = 0; it < MAX_ITER; it++) {
+    gettimeofday(&start, NULL);
+    matrixMult( C, A, B, n );
+    gettimeofday(&end, NULL);
+
+    time = ( (end.tv_sec  - start.tv_sec)  * 1000.0 +  /* sec to ms */
+             (end.tv_usec - start.tv_usec) / 1000.0 ); /* us to ms */
+               
+    printf("Iter: %d Time: %f ms\n", it, time);
+  }
+
+  /* we noeed to use the result -- verify it */
+  for (int i = 0; i < n; i++) {             /* rows */
+    for (int j = 0; j < n; j++) {           /* cols */
+
+      float gold = 0;
+
+      for (int k = 0; k < n; k++) {         /* accumulate products */
+        gold += A[ sub2ind(i,k,n) ] * B[ sub2ind(k,j,n) ];
+      }
+
+      assert( (gold - C[sub2ind(i,j,n)]) < 1e-3 );
+      
+    }
+  }
+}
+