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diff --git a/x86-bare-metal/mbr-pure-zig/bios.zig b/x86-bare-metal/mbr-pure-zig/bios.zig
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+/// BIOS starts with video mode 0h.
+///   * 80x25 text mode
+///   * 16 colors (4bit)
+/// http://www.ctyme.com/intr/rb-0069.htm
+pub const COLS = 80;
+pub const ROWS = 25;
+
+/// BIOS CALL - video teletype output.
+/// http://www.ctyme.com/intr/rb-0106.htm
+pub fn putc(c: u8) void {
+    // ah=0eh (call nr)
+    // al=c   (ascii char to write)
+    const ax = (@as(u16, 0xe) << 8) | c;
+
+    _ = asm volatile (
+        \\int $0x10
+        : // No outputs.
+        : [a] "{ax}" (ax), // BIOS call number + char to write.
+        : "cc"
+    );
+
+    // On linefeed also write a carriage return to move to column 0.
+    if (c == '\n') {
+        putc('\r');
+    }
+}
+
+/// BIOS CALL - video set cursor position.
+/// http://www.ctyme.com/intr/rb-0087.htm
+pub fn set_pos(r: u8) void {
+    // dh=r (cursor row)
+    // dl=0 (cursor col)
+    const dx = @as(u16, r) << 8 | 0;
+
+    _ = asm volatile (
+        \\int $0x10
+        : // No outputs.
+        : [a] "{ax}" (0x200), // BIOS call number.
+          [b] "{bx}" (0x0), // Page number.
+          [d] "{dx}" (dx), // Position.
+        : "cc"
+    );
+}
+
+/// BIOS CALL - video scroll up
+/// http://www.ctyme.com/intr/rb-0096.htm
+pub fn scroll_up() void {
+    // ah=06h (call nr)
+    // al=1   (rows to scroll)
+    const ax = (@as(u16, 0x6) << 8) | 1;
+
+    // dh=ROWS-1 (row lower right corner)
+    // dl=COLS-1 (col lower right corner)
+    const dx = (@as(u16, ROWS - 1) << 8) | (COLS - 1);
+
+    _ = asm volatile (
+        \\int $0x10
+        : // No outputs.
+        : [a] "{ax}" (ax), // BIOS call number + rows to scroll.
+          [p] "{dx}" (dx), // Row + col lower right corner.
+          [b] "{bx}" (0x0700), // Attribute, dark bg, white fg.
+          [c] "{cx}" (0), // Row + col upper left corner.
+        : "cc"
+    );
+}