diff --git a/src/core/io.zig b/src/core/io.zig
index c6dd1cb..48dee34 100644
--- a/src/core/io.zig
+++ b/src/core/io.zig
@@ -204,6 +204,38 @@ test "Check memory begins with" {
     try testing.expect(!begins(u8, &.{69, 89, 42, 0}, bytes_sequence));
 }
 
+///
+/// Returns a sliced reference of the raw bytes in `pointer`.
+///
+/// **Note** that passing a slice will convert it to a byte slice.
+///
+pub fn bytes(pointer: anytype) switch (@typeInfo(@TypeOf(pointer))) {
+    .Pointer => |info| if (info.is_const) []const u8 else []u8,
+    else => @compileError("`pointer` must be a pointer type"),
+} {
+    const Pointer = @TypeOf(pointer);
+    const pointer_info = @typeInfo(Pointer).Pointer;
+
+    switch (pointer_info.size) {
+        .Many => @compileError("`pointer` cannot be an unbound pointer type"),
+        .C => @compileError("`pointer` cannot be a C-style pointer"),
+
+        .One => return @ptrCast(if (pointer_info.is_const) [*]const u8
+                else [*]u8, pointer)[0 .. @sizeOf(Pointer)],
+
+        .Slice => return @ptrCast(if (pointer_info.is_const) [*]const u8 else
+            [*]u8, pointer.ptr)[0 .. (@sizeOf(Pointer) * pointer.len)],
+    }
+}
+
+test "Bytes of types" {
+    const testing = std.testing;
+
+    var foo: u32 = 10;
+
+    testing.expectEqual(bytes(&foo), 0x0a);
+}
+
 ///
 /// Returns `true` if `this` is the same length and contains the same data as `that`, otherwise
 /// `false`.
diff --git a/src/oar/main.zig b/src/oar/main.zig
index 15f5a77..bc1d5ea 100644
--- a/src/oar/main.zig
+++ b/src/oar/main.zig
@@ -5,7 +5,13 @@ const std = @import("std");
 ///
 ///
 pub const Archive = struct {
+    pub fn deinit(archive: *Archive) {
 
+    }
+
+    pub fn init(file_system: *const sys.FileSystem, file_path: sys.Path) {
+
+    }
 };
 
 ///
diff --git a/src/ona/oar.zig b/src/ona/oar.zig
new file mode 100644
index 0000000..d24da0d
--- /dev/null
+++ b/src/ona/oar.zig
@@ -0,0 +1,138 @@
+const core = @import("./core.zig");
+const sys = @import("./sys.zig");
+
+///
+///
+///
+pub const Archive = struct {
+    file_system: *const sys.FileSystem,
+    archive_path: sys.Path,
+
+    ///
+    ///
+    ///
+    const Header = extern struct {
+        signature: [signature_magic.len]u8,
+        revision: u8,
+        entry_offset: u64,
+        padding: [500]u8 = std.mem.zeroes([500]u8),
+
+        ///
+        /// Magic identifier used to validate [Entry] data.
+        ///
+        const signature_magic = [3]u8{'o', 'a', 'r'};
+
+        comptime {
+            const size = @sizeOf(@This());
+
+            if (size != 512)
+                @compileError("Header is " ++
+                    std.fmt.comptimePrint("{d}", .{entry_size}) ++ " bytes");
+        }
+    };
+
+    ///
+    /// An entry block of an Oar archive file.
+    ///
+    /// Typically, following the block in memory is the file data it holds the meta-information for.
+    ///
+    const Entry = extern struct {
+        signature: [signature_magic.len]u8 = signature_magic,
+        revision: u8,
+        path: Path,
+        file_size: u64,
+        absolute_offset: u64,
+        padding: [232]u8 = std.mem.zeroes([232]u8),
+
+        comptime {
+            const entry_size = @sizeOf(Entry);
+
+            if (entry_size != 512)
+                @compileError("Entry is " ++
+                    std.fmt.comptimePrint("{d}", .{entry_size}) ++ " bytes");
+        }
+    };
+
+    ///
+    ///
+    ///
+    pub const OpenError = error {
+        FileNotFound,
+        EntryNotFound,
+        UnsupportedArchive,
+    };
+
+    ///
+    ///
+    ///
+    pub fn open(archive: Archive, entry_path: Path) OpenError!EntryAccess {
+        const file_access = try archive.file_system.open(entry_path, .readonly);
+
+        errdefer file_access.close();
+
+        var header = std.mem.zeroes(Header);
+        const header_size = @sizeOf(Header);
+        const io = core.io;
+
+        // Validate header.
+        if ((try file_access.read(io.bytes(&header)) != header_size) or header
+            (!core.io.equals(u8, &header.signature, &Header.signature_magic)) or
+            (header.revision != revision) or
+            (header.entry_offset <= header_size)) return error.UnsupportedArchive;
+
+        // Go to file table.
+        try file_access.seek(header.entry_offset);
+
+        // Read file table.
+        var entry_buffer = std.mem.zeroes([8]Entry);
+        var bytes_read = try file_access.read(io.bytes(&entry_buffer));
+
+        while (@mod(bytes_read, @sizeOf(Entry)) == 0) {
+            for (entry_buffer[0 .. (bytes_read / @sizeOf(Entry))]) |entry| {
+                if (entry.path.equals(entry_path)) {
+                    file_access.seek(entry.file_offset);
+
+                    return Entry{
+                        .file_access = file_access,
+                    };
+                }
+            }
+
+            bytes_read = try file_access.read(io.bytes(&entry_buffer));
+        }
+
+        var head = std.mem.zeroes(usize);
+        var tail = (header.file_count - 1);
+
+        while (head <= tail) {
+            const midpoint = (head + (tail - head) / 2);
+
+            const comparison = entry_path.compare(arr[m]));
+
+            if (comparison == 0) return midpoint;
+
+            if (comparison > 0) {
+                // If x greater, ignore left half
+                head = (midpoint + 1);
+            } else {
+                // If x is smaller, ignore right half
+                tail = (midpoint - 1);
+            }
+        }
+
+        return error.EntryNotFound;
+    }
+};
+
+pub const EntryAccess = struct {
+    file_access: FileAccess,
+
+    pub fn close(entry: Entry) void {
+        entry.file_access.close();
+    }
+};
+
+///
+///
+///
+const revision = 0;
diff --git a/src/ona/sys.zig b/src/ona/sys.zig
index 9b04750..63f3ed3 100644
--- a/src/ona/sys.zig
+++ b/src/ona/sys.zig
@@ -100,37 +100,6 @@ pub const FileSystem = union(enum) {
     native: []const u8,
     archive: Archive,
 
-    ///
-    /// Archive file system information.
-    ///
-    const Archive = struct {
-        file_access: core.io.FileAccess,
-        index_cache: IndexCache,
-        entry_table: [max_open_entries]Entry = std.mem.zeroes([max_open_entries]Entry),
-
-        ///
-        /// Hard limit on the maximum number of entries open at once.
-        ///
-        const max_open_entries = 16;
-
-        ///
-        /// Stateful extension of an [oar.Entry].
-        ///
-        const Entry = struct {
-            owner: ?*core.io.FileAccess,
-            cursor: u64,
-            header: oar.Entry,
-        };
-
-        ///
-        /// Table cache for associating [oar.Path] values with offsets to entries in a given file.
-        ///
-        const IndexCache = core.table.Hashed(oar.Path, u64, .{
-            .equals = oar.Path.equals,
-            .hash = oar.Path.hash,
-        });
-    };
-
     ///
     /// With files typically being backed by a block device, they can produce a variety of errors -
     /// from physical to virtual errors - these are all encapsulated by the API as general
@@ -172,7 +141,9 @@ pub const FileSystem = union(enum) {
     /// Returns a [FileAccess] reference that provides access to the file referenced by `path`or a
     /// [OpenError] if it failed.
     ///
-    pub fn open(file_system: *FileSystem, path: Path, mode: OpenMode) OpenError!core.io.FileAccess {
+    pub fn open(file_system: *const FileSystem, path: Path,
+        mode: OpenMode) OpenError!core.io.FileAccess {
+
         switch (file_system.*) {
             .archive => |*archive| {
                 if (mode != .readonly) return error.ModeUnsupported;